redirect_canonical

The timeline below displays how wordpress function redirect_canonical has changed across different WordPress versions. If a version is not listed, refer to the next available version below.

WordPress Version: 6.5

/**
 * Canonical API to handle WordPress Redirecting
 *
 * Based on "Permalink Redirect" from Scott Yang and "Enforce www. Preference"
 * by Mark Jaquith
 *
 * @package WordPress
 * @since 2.3.0
 */
/**
 * Redirects incoming links to the proper URL based on the site url.
 *
 * Search engines consider www.somedomain.com and somedomain.com to be two
 * different URLs when they both go to the same location. This SEO enhancement
 * prevents penalty for duplicate content by redirecting all incoming links to
 * one or the other.
 *
 * Prevents redirection for feeds, trackbacks, searches, and
 * admin URLs. Does not redirect on non-pretty-permalink-supporting IIS 7+,
 * page/post previews, WP admin, Trackbacks, robots.txt, favicon.ico, searches,
 * or on POST requests.
 *
 * Will also attempt to find the correct link when a user enters a URL that does
 * not exist based on exact WordPress query. Will instead try to parse the URL
 * or query in an attempt to figure the correct page to go to.
 *
 * @since 2.3.0
 *
 * @global WP_Rewrite $wp_rewrite WordPress rewrite component.
 * @global bool       $is_IIS
 * @global WP_Query   $wp_query   WordPress Query object.
 * @global wpdb       $wpdb       WordPress database abstraction object.
 * @global WP         $wp         Current WordPress environment instance.
 *
 * @param string $requested_url Optional. The URL that was requested, used to
 *                              figure if redirect is needed.
 * @param bool   $do_redirect   Optional. Redirect to the new URL.
 * @return string|void The string of the URL, if redirect needed.
 */
function redirect_canonical($requested_url = null, $do_redirect = true)
{
    global $wp_rewrite, $is_IIS, $wp_query, $wpdb, $wp;
    if (isset($_SERVER['REQUEST_METHOD']) && !in_array(strtoupper($_SERVER['REQUEST_METHOD']), array('GET', 'HEAD'), true)) {
        return;
    }
    /*
     * If we're not in wp-admin and the post has been published and preview nonce
     * is non-existent or invalid then no need for preview in query.
     */
    if (is_preview() && get_query_var('p') && 'publish' === get_post_status(get_query_var('p'))) {
        if (!isset($_GET['preview_id']) || !isset($_GET['preview_nonce']) || !wp_verify_nonce($_GET['preview_nonce'], 'post_preview_' . (int) $_GET['preview_id'])) {
            $wp_query->is_preview = false;
        }
    }
    if (is_admin() || is_search() || is_preview() || is_trackback() || is_favicon() || $is_IIS && !iis7_supports_permalinks()) {
        return;
    }
    if (!$requested_url && isset($_SERVER['HTTP_HOST'])) {
        // Build the URL in the address bar.
        $requested_url = is_ssl() ? 'https://' : 'http://';
        $requested_url .= $_SERVER['HTTP_HOST'];
        $requested_url .= $_SERVER['REQUEST_URI'];
    }
    $original = parse_url($requested_url);
    if (false === $original) {
        return;
    }
    $redirect = $original;
    $redirect_url = false;
    $redirect_obj = false;
    // Notice fixing.
    if (!isset($redirect['path'])) {
        $redirect['path'] = '';
    }
    if (!isset($redirect['query'])) {
        $redirect['query'] = '';
    }
    /*
     * If the original URL ended with non-breaking spaces, they were almost
     * certainly inserted by accident. Let's remove them, so the reader doesn't
     * see a 404 error with no obvious cause.
     */
    $redirect['path'] = preg_replace('|(%C2%A0)+$|i', '', $redirect['path']);
    // It's not a preview, so remove it from URL.
    if (get_query_var('preview')) {
        $redirect['query'] = remove_query_arg('preview', $redirect['query']);
    }
    $post_id = get_query_var('p');
    if (is_feed() && $post_id) {
        $redirect_url = get_post_comments_feed_link($post_id, get_query_var('feed'));
        $redirect_obj = get_post($post_id);
        if ($redirect_url) {
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type', 'feed'), $redirect_url);
            $redirect['path'] = parse_url($redirect_url, PHP_URL_PATH);
        }
    }
    if (is_singular() && $wp_query->post_count < 1 && $post_id) {
        $vars = $wpdb->get_results($wpdb->prepare("SELECT post_type, post_parent FROM {$wpdb->posts} WHERE ID = %d", $post_id));
        if (!empty($vars[0])) {
            $vars = $vars[0];
            if ('revision' === $vars->post_type && $vars->post_parent > 0) {
                $post_id = $vars->post_parent;
            }
            $redirect_url = get_permalink($post_id);
            $redirect_obj = get_post($post_id);
            if ($redirect_url) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    }
    // These tests give us a WP-generated permalink.
    if (is_404()) {
        // Redirect ?page_id, ?p=, ?attachment_id= to their respective URLs.
        $post_id = max(get_query_var('p'), get_query_var('page_id'), get_query_var('attachment_id'));
        $redirect_post = $post_id ? get_post($post_id) : false;
        if ($redirect_post) {
            $post_type_obj = get_post_type_object($redirect_post->post_type);
            if ($post_type_obj && $post_type_obj->public && 'auto-draft' !== $redirect_post->post_status) {
                $redirect_url = get_permalink($redirect_post);
                $redirect_obj = get_post($redirect_post);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
        $year = get_query_var('year');
        $month = get_query_var('monthnum');
        $day = get_query_var('day');
        if ($year && $month && $day) {
            $date = sprintf('%04d-%02d-%02d', $year, $month, $day);
            if (!wp_checkdate($month, $day, $year, $date)) {
                $redirect_url = get_month_link($year, $month);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum', 'day'), $redirect_url);
            }
        } elseif ($year && $month && $month > 12) {
            $redirect_url = get_year_link($year);
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum'), $redirect_url);
        }
        // Strip off non-existing <!--nextpage--> links from single posts or pages.
        if (get_query_var('page')) {
            $post_id = 0;
            if ($wp_query->queried_object instanceof WP_Post) {
                $post_id = $wp_query->queried_object->ID;
            } elseif ($wp_query->post) {
                $post_id = $wp_query->post->ID;
            }
            if ($post_id) {
                $redirect_url = get_permalink($post_id);
                $redirect_obj = get_post($post_id);
                $redirect['path'] = rtrim($redirect['path'], (int) get_query_var('page') . '/');
                $redirect['query'] = remove_query_arg('page', $redirect['query']);
            }
        }
        if (!$redirect_url) {
            $redirect_url = redirect_guess_404_permalink();
            if ($redirect_url) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('page', 'feed', 'p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    } elseif (is_object($wp_rewrite) && $wp_rewrite->using_permalinks()) {
        // Rewriting of old ?p=X, ?m=2004, ?m=200401, ?m=20040101.
        if (is_attachment() && !array_diff(array_keys($wp->query_vars), array('attachment', 'attachment_id')) && !$redirect_url) {
            if (!empty($_GET['attachment_id'])) {
                $redirect_url = get_attachment_link(get_query_var('attachment_id'));
                $redirect_obj = get_post(get_query_var('attachment_id'));
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('attachment_id', $redirect['query']);
                }
            } else {
                $redirect_url = get_attachment_link();
                $redirect_obj = get_post();
            }
        } elseif (is_single() && !empty($_GET['p']) && !$redirect_url) {
            $redirect_url = get_permalink(get_query_var('p'));
            $redirect_obj = get_post(get_query_var('p'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg(array('p', 'post_type'), $redirect['query']);
            }
        } elseif (is_single() && !empty($_GET['name']) && !$redirect_url) {
            $redirect_url = get_permalink($wp_query->get_queried_object_id());
            $redirect_obj = get_post($wp_query->get_queried_object_id());
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('name', $redirect['query']);
            }
        } elseif (is_page() && !empty($_GET['page_id']) && !$redirect_url) {
            $redirect_url = get_permalink(get_query_var('page_id'));
            $redirect_obj = get_post(get_query_var('page_id'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (is_page() && !is_feed() && !$redirect_url && 'page' === get_option('show_on_front') && get_queried_object_id() === (int) get_option('page_on_front')) {
            $redirect_url = home_url('/');
        } elseif (is_home() && !empty($_GET['page_id']) && !$redirect_url && 'page' === get_option('show_on_front') && get_query_var('page_id') === (int) get_option('page_for_posts')) {
            $redirect_url = get_permalink(get_option('page_for_posts'));
            $redirect_obj = get_post(get_option('page_for_posts'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (!empty($_GET['m']) && (is_year() || is_month() || is_day())) {
            $m = get_query_var('m');
            switch (strlen($m)) {
                case 4:
                    // Yearly.
                    $redirect_url = get_year_link($m);
                    break;
                case 6:
                    // Monthly.
                    $redirect_url = get_month_link(substr($m, 0, 4), substr($m, 4, 2));
                    break;
                case 8:
                    // Daily.
                    $redirect_url = get_day_link(substr($m, 0, 4), substr($m, 4, 2), substr($m, 6, 2));
                    break;
            }
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('m', $redirect['query']);
            }
            // Now moving on to non ?m=X year/month/day links.
        } elseif (is_date()) {
            $year = get_query_var('year');
            $month = get_query_var('monthnum');
            $day = get_query_var('day');
            if (is_day() && $year && $month && !empty($_GET['day'])) {
                $redirect_url = get_day_link($year, $month, $day);
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg(array('year', 'monthnum', 'day'), $redirect['query']);
                }
            } elseif (is_month() && $year && !empty($_GET['monthnum'])) {
                $redirect_url = get_month_link($year, $month);
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg(array('year', 'monthnum'), $redirect['query']);
                }
            } elseif (is_year() && !empty($_GET['year'])) {
                $redirect_url = get_year_link($year);
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('year', $redirect['query']);
                }
            }
        } elseif (is_author() && !empty($_GET['author']) && is_string($_GET['author']) && preg_match('|^[0-9]+$|', $_GET['author'])) {
            $author = get_userdata(get_query_var('author'));
            if (false !== $author && $wpdb->get_var($wpdb->prepare("SELECT ID FROM {$wpdb->posts} WHERE {$wpdb->posts}.post_author = %d AND {$wpdb->posts}.post_status = 'publish' LIMIT 1", $author->ID))) {
                $redirect_url = get_author_posts_url($author->ID, $author->user_nicename);
                $redirect_obj = $author;
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('author', $redirect['query']);
                }
            }
        } elseif (is_category() || is_tag() || is_tax()) {
            // Terms (tags/categories).
            $term_count = 0;
            foreach ($wp_query->tax_query->queried_terms as $tax_query) {
                if (isset($tax_query['terms']) && is_countable($tax_query['terms'])) {
                    $term_count += count($tax_query['terms']);
                }
            }
            $obj = $wp_query->get_queried_object();
            if ($term_count <= 1 && !empty($obj->term_id)) {
                $tax_url = get_term_link((int) $obj->term_id, $obj->taxonomy);
                if ($tax_url && !is_wp_error($tax_url)) {
                    if (!empty($redirect['query'])) {
                        // Strip taxonomy query vars off the URL.
                        $qv_remove = array('term', 'taxonomy');
                        if (is_category()) {
                            $qv_remove[] = 'category_name';
                            $qv_remove[] = 'cat';
                        } elseif (is_tag()) {
                            $qv_remove[] = 'tag';
                            $qv_remove[] = 'tag_id';
                        } else {
                            // Custom taxonomies will have a custom query var, remove those too.
                            $tax_obj = get_taxonomy($obj->taxonomy);
                            if (false !== $tax_obj->query_var) {
                                $qv_remove[] = $tax_obj->query_var;
                            }
                        }
                        $rewrite_vars = array_diff(array_keys($wp_query->query), array_keys($_GET));
                        // Check to see if all the query vars are coming from the rewrite, none are set via $_GET.
                        if (!array_diff($rewrite_vars, array_keys($_GET))) {
                            // Remove all of the per-tax query vars.
                            $redirect['query'] = remove_query_arg($qv_remove, $redirect['query']);
                            // Create the destination URL for this taxonomy.
                            $tax_url = parse_url($tax_url);
                            if (!empty($tax_url['query'])) {
                                // Taxonomy accessible via ?taxonomy=...&term=... or any custom query var.
                                parse_str($tax_url['query'], $query_vars);
                                $redirect['query'] = add_query_arg($query_vars, $redirect['query']);
                            } else {
                                // Taxonomy is accessible via a "pretty URL".
                                $redirect['path'] = $tax_url['path'];
                            }
                        } else {
                            // Some query vars are set via $_GET. Unset those from $_GET that exist via the rewrite.
                            foreach ($qv_remove as $_qv) {
                                if (isset($rewrite_vars[$_qv])) {
                                    $redirect['query'] = remove_query_arg($_qv, $redirect['query']);
                                }
                            }
                        }
                    }
                }
            }
        } elseif (is_single() && str_contains($wp_rewrite->permalink_structure, '%category%')) {
            $category_name = get_query_var('category_name');
            if ($category_name) {
                $category = get_category_by_path($category_name);
                if (!$category || is_wp_error($category) || !has_term($category->term_id, 'category', $wp_query->get_queried_object_id())) {
                    $redirect_url = get_permalink($wp_query->get_queried_object_id());
                    $redirect_obj = get_post($wp_query->get_queried_object_id());
                }
            }
        }
        // Post paging.
        if (is_singular() && get_query_var('page')) {
            $page = get_query_var('page');
            if (!$redirect_url) {
                $redirect_url = get_permalink(get_queried_object_id());
                $redirect_obj = get_post(get_queried_object_id());
            }
            if ($page > 1) {
                $redirect_url = trailingslashit($redirect_url);
                if (is_front_page()) {
                    $redirect_url .= user_trailingslashit("{$wp_rewrite->pagination_base}/{$page}", 'paged');
                } else {
                    $redirect_url .= user_trailingslashit($page, 'single_paged');
                }
            }
            $redirect['query'] = remove_query_arg('page', $redirect['query']);
        }
        if (get_query_var('sitemap')) {
            $redirect_url = get_sitemap_url(get_query_var('sitemap'), get_query_var('sitemap-subtype'), get_query_var('paged'));
            $redirect['query'] = remove_query_arg(array('sitemap', 'sitemap-subtype', 'paged'), $redirect['query']);
        } elseif (get_query_var('paged') || is_feed() || get_query_var('cpage')) {
            // Paging and feeds.
            $paged = get_query_var('paged');
            $feed = get_query_var('feed');
            $cpage = get_query_var('cpage');
            while (preg_match("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", $redirect['path']) || preg_match('#/(comments/?)?(feed|rss2?|rdf|atom)(/+)?$#', $redirect['path']) || preg_match("#/{$wp_rewrite->comments_pagination_base}-[0-9]+(/+)?\$#", $redirect['path'])) {
                // Strip off any existing paging.
                $redirect['path'] = preg_replace("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", '/', $redirect['path']);
                // Strip off feed endings.
                $redirect['path'] = preg_replace('#/(comments/?)?(feed|rss2?|rdf|atom)(/+|$)#', '/', $redirect['path']);
                // Strip off any existing comment paging.
                $redirect['path'] = preg_replace("#/{$wp_rewrite->comments_pagination_base}-[0-9]+?(/+)?\$#", '/', $redirect['path']);
            }
            $addl_path = '';
            $default_feed = get_default_feed();
            if (is_feed() && in_array($feed, $wp_rewrite->feeds, true)) {
                $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                if (!is_singular() && get_query_var('withcomments')) {
                    $addl_path .= 'comments/';
                }
                if ('rss' === $default_feed && 'feed' === $feed || 'rss' === $feed) {
                    $format = ('rss2' === $default_feed) ? '' : 'rss2';
                } else {
                    $format = ($default_feed === $feed || 'feed' === $feed) ? '' : $feed;
                }
                $addl_path .= user_trailingslashit('feed/' . $format, 'feed');
                $redirect['query'] = remove_query_arg('feed', $redirect['query']);
            } elseif (is_feed() && 'old' === $feed) {
                $old_feed_files = array('wp-atom.php' => 'atom', 'wp-commentsrss2.php' => 'comments_rss2', 'wp-feed.php' => $default_feed, 'wp-rdf.php' => 'rdf', 'wp-rss.php' => 'rss2', 'wp-rss2.php' => 'rss2');
                if (isset($old_feed_files[basename($redirect['path'])])) {
                    $redirect_url = get_feed_link($old_feed_files[basename($redirect['path'])]);
                    wp_redirect($redirect_url, 301);
                    die;
                }
            }
            if ($paged > 0) {
                $redirect['query'] = remove_query_arg('paged', $redirect['query']);
                if (!is_feed()) {
                    if (!is_single()) {
                        $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                        if ($paged > 1) {
                            $addl_path .= user_trailingslashit("{$wp_rewrite->pagination_base}/{$paged}", 'paged');
                        }
                    }
                } elseif ($paged > 1) {
                    $redirect['query'] = add_query_arg('paged', $paged, $redirect['query']);
                }
            }
            $default_comments_page = get_option('default_comments_page');
            if (get_option('page_comments') && ('newest' === $default_comments_page && $cpage > 0 || 'newest' !== $default_comments_page && $cpage > 1)) {
                $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                $addl_path .= user_trailingslashit($wp_rewrite->comments_pagination_base . '-' . $cpage, 'commentpaged');
                $redirect['query'] = remove_query_arg('cpage', $redirect['query']);
            }
            // Strip off trailing /index.php/.
            $redirect['path'] = preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/?$|', '/', $redirect['path']);
            $redirect['path'] = user_trailingslashit($redirect['path']);
            if (!empty($addl_path) && $wp_rewrite->using_index_permalinks() && !str_contains($redirect['path'], '/' . $wp_rewrite->index . '/')) {
                $redirect['path'] = trailingslashit($redirect['path']) . $wp_rewrite->index . '/';
            }
            if (!empty($addl_path)) {
                $redirect['path'] = trailingslashit($redirect['path']) . $addl_path;
            }
            $redirect_url = $redirect['scheme'] . '://' . $redirect['host'] . $redirect['path'];
        }
        if ('wp-register.php' === basename($redirect['path'])) {
            if (is_multisite()) {
                /** This filter is documented in wp-login.php */
                $redirect_url = apply_filters('wp_signup_location', network_site_url('wp-signup.php'));
            } else {
                $redirect_url = wp_registration_url();
            }
            wp_redirect($redirect_url, 301);
            die;
        }
    }
    $is_attachment_redirect = false;
    if (is_attachment() && !get_option('wp_attachment_pages_enabled')) {
        $attachment_id = get_query_var('attachment_id');
        $attachment_post = get_post($attachment_id);
        $attachment_parent_id = $attachment_post ? $attachment_post->post_parent : 0;
        $attachment_url = wp_get_attachment_url($attachment_id);
        if ($attachment_url !== $redirect_url) {
            /*
             * If an attachment is attached to a post, it inherits the parent post's status. Fetch the
             * parent post to check its status later.
             */
            if ($attachment_parent_id) {
                $redirect_obj = get_post($attachment_parent_id);
            }
            $redirect_url = $attachment_url;
        }
        $is_attachment_redirect = true;
    }
    $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    // Tack on any additional query vars.
    if ($redirect_url && !empty($redirect['query'])) {
        parse_str($redirect['query'], $_parsed_query);
        $redirect = parse_url($redirect_url);
        if (!empty($_parsed_query['name']) && !empty($redirect['query'])) {
            parse_str($redirect['query'], $_parsed_redirect_query);
            if (empty($_parsed_redirect_query['name'])) {
                unset($_parsed_query['name']);
            }
        }
        $_parsed_query = array_combine(rawurlencode_deep(array_keys($_parsed_query)), rawurlencode_deep(array_values($_parsed_query)));
        $redirect_url = add_query_arg($_parsed_query, $redirect_url);
    }
    if ($redirect_url) {
        $redirect = parse_url($redirect_url);
    }
    // www.example.com vs. example.com
    $user_home = parse_url(home_url());
    if (!empty($user_home['host'])) {
        $redirect['host'] = $user_home['host'];
    }
    if (empty($user_home['path'])) {
        $user_home['path'] = '/';
    }
    // Handle ports.
    if (!empty($user_home['port'])) {
        $redirect['port'] = $user_home['port'];
    } else {
        unset($redirect['port']);
    }
    // Trailing /index.php.
    $redirect['path'] = preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/*?$|', '/', $redirect['path']);
    $punctuation_pattern = implode('|', array_map('preg_quote', array(
        ' ',
        '%20',
        // Space.
        '!',
        '%21',
        // Exclamation mark.
        '"',
        '%22',
        // Double quote.
        "'",
        '%27',
        // Single quote.
        '(',
        '%28',
        // Opening bracket.
        ')',
        '%29',
        // Closing bracket.
        ',',
        '%2C',
        // Comma.
        '.',
        '%2E',
        // Period.
        ';',
        '%3B',
        // Semicolon.
        '{',
        '%7B',
        // Opening curly bracket.
        '}',
        '%7D',
        // Closing curly bracket.
        '%E2%80%9C',
        // Opening curly quote.
        '%E2%80%9D',
    )));
    // Remove trailing spaces and end punctuation from the path.
    $redirect['path'] = preg_replace("#({$punctuation_pattern})+\$#", '', $redirect['path']);
    if (!empty($redirect['query'])) {
        // Remove trailing spaces and end punctuation from certain terminating query string args.
        $redirect['query'] = preg_replace("#((^|&)(p|page_id|cat|tag)=[^&]*?)({$punctuation_pattern})+\$#", '$1', $redirect['query']);
        // Clean up empty query strings.
        $redirect['query'] = trim(preg_replace('#(^|&)(p|page_id|cat|tag)=?(&|$)#', '&', $redirect['query']), '&');
        // Redirect obsolete feeds.
        $redirect['query'] = preg_replace('#(^|&)feed=rss(&|$)#', '$1feed=rss2$2', $redirect['query']);
        // Remove redundant leading ampersands.
        $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    }
    // Strip /index.php/ when we're not using PATHINFO permalinks.
    if (!$wp_rewrite->using_index_permalinks()) {
        $redirect['path'] = str_replace('/' . $wp_rewrite->index . '/', '/', $redirect['path']);
    }
    // Trailing slashes.
    if (is_object($wp_rewrite) && $wp_rewrite->using_permalinks() && !$is_attachment_redirect && !is_404() && (!is_front_page() || is_front_page() && get_query_var('paged') > 1)) {
        $user_ts_type = '';
        if (get_query_var('paged') > 0) {
            $user_ts_type = 'paged';
        } else {
            foreach (array('single', 'category', 'page', 'day', 'month', 'year', 'home') as $type) {
                $func = 'is_' . $type;
                if (call_user_func($func)) {
                    $user_ts_type = $type;
                    break;
                }
            }
        }
        $redirect['path'] = user_trailingslashit($redirect['path'], $user_ts_type);
    } elseif (is_front_page()) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Remove trailing slash for robots.txt or sitemap requests.
    if (is_robots() || !empty(get_query_var('sitemap')) || !empty(get_query_var('sitemap-stylesheet'))) {
        $redirect['path'] = untrailingslashit($redirect['path']);
    }
    // Strip multiple slashes out of the URL.
    if (str_contains($redirect['path'], '//')) {
        $redirect['path'] = preg_replace('|/+|', '/', $redirect['path']);
    }
    // Always trailing slash the Front Page URL.
    if (trailingslashit($redirect['path']) === trailingslashit($user_home['path'])) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    $original_host_low = strtolower($original['host']);
    $redirect_host_low = strtolower($redirect['host']);
    /*
     * Ignore differences in host capitalization, as this can lead to infinite redirects.
     * Only redirect no-www <=> yes-www.
     */
    if ($original_host_low === $redirect_host_low || 'www.' . $original_host_low !== $redirect_host_low && 'www.' . $redirect_host_low !== $original_host_low) {
        $redirect['host'] = $original['host'];
    }
    $compare_original = array($original['host'], $original['path']);
    if (!empty($original['port'])) {
        $compare_original[] = $original['port'];
    }
    if (!empty($original['query'])) {
        $compare_original[] = $original['query'];
    }
    $compare_redirect = array($redirect['host'], $redirect['path']);
    if (!empty($redirect['port'])) {
        $compare_redirect[] = $redirect['port'];
    }
    if (!empty($redirect['query'])) {
        $compare_redirect[] = $redirect['query'];
    }
    if ($compare_original !== $compare_redirect) {
        $redirect_url = $redirect['scheme'] . '://' . $redirect['host'];
        if (!empty($redirect['port'])) {
            $redirect_url .= ':' . $redirect['port'];
        }
        $redirect_url .= $redirect['path'];
        if (!empty($redirect['query'])) {
            $redirect_url .= '?' . $redirect['query'];
        }
    }
    if (!$redirect_url || $redirect_url === $requested_url) {
        return;
    }
    // Hex-encoded octets are case-insensitive.
    if (str_contains($requested_url, '%')) {
        if (!function_exists('lowercase_octets')) {
            /**
             * Converts the first hex-encoded octet match to lowercase.
             *
             * @since 3.1.0
             * @ignore
             *
             * @param array $matches Hex-encoded octet matches for the requested URL.
             * @return string Lowercased version of the first match.
             */
            function lowercase_octets($matches)
            {
                return strtolower($matches[0]);
            }
        }
        $requested_url = preg_replace_callback('|%[a-fA-F0-9][a-fA-F0-9]|', 'lowercase_octets', $requested_url);
    }
    if ($redirect_obj instanceof WP_Post) {
        $post_status_obj = get_post_status_object(get_post_status($redirect_obj));
        /*
         * Unset the redirect object and URL if they are not readable by the user.
         * This condition is a little confusing as the condition needs to pass if
         * the post is not readable by the user. That's why there are ! (not) conditions
         * throughout.
         */
        if (!($post_status_obj->private && current_user_can('read_post', $redirect_obj->ID)) && !is_post_publicly_viewable($redirect_obj)) {
            $redirect_obj = false;
            $redirect_url = false;
        }
    }
    /**
     * Filters the canonical redirect URL.
     *
     * Returning false to this filter will cancel the redirect.
     *
     * @since 2.3.0
     *
     * @param string $redirect_url  The redirect URL.
     * @param string $requested_url The requested URL.
     */
    $redirect_url = apply_filters('redirect_canonical', $redirect_url, $requested_url);
    // Yes, again -- in case the filter aborted the request.
    if (!$redirect_url || strip_fragment_from_url($redirect_url) === strip_fragment_from_url($requested_url)) {
        return;
    }
    if ($do_redirect) {
        // Protect against chained redirects.
        if (!redirect_canonical($redirect_url, false)) {
            wp_redirect($redirect_url, 301);
            exit;
        } else {
            // Debug.
            // die("1: $redirect_url<br />2: " . redirect_canonical( $redirect_url, false ) );
            return;
        }
    } else {
        return $redirect_url;
    }
}

WordPress Version: 4.3

/**
 * Canonical API to handle WordPress Redirecting
 *
 * Based on "Permalink Redirect" from Scott Yang and "Enforce www. Preference"
 * by Mark Jaquith
 *
 * @package WordPress
 * @since 2.3.0
 */
/**
 * Redirects incoming links to the proper URL based on the site url.
 *
 * Search engines consider www.somedomain.com and somedomain.com to be two
 * different URLs when they both go to the same location. This SEO enhancement
 * prevents penalty for duplicate content by redirecting all incoming links to
 * one or the other.
 *
 * Prevents redirection for feeds, trackbacks, searches, and
 * admin URLs. Does not redirect on non-pretty-permalink-supporting IIS 7+,
 * page/post previews, WP admin, Trackbacks, robots.txt, favicon.ico, searches,
 * or on POST requests.
 *
 * Will also attempt to find the correct link when a user enters a URL that does
 * not exist based on exact WordPress query. Will instead try to parse the URL
 * or query in an attempt to figure the correct page to go to.
 *
 * @since 2.3.0
 *
 * @global WP_Rewrite $wp_rewrite WordPress rewrite component.
 * @global bool       $is_IIS
 * @global WP_Query   $wp_query   WordPress Query object.
 * @global wpdb       $wpdb       WordPress database abstraction object.
 * @global WP         $wp         Current WordPress environment instance.
 *
 * @param string $requested_url Optional. The URL that was requested, used to
 *                              figure if redirect is needed.
 * @param bool   $do_redirect   Optional. Redirect to the new URL.
 * @return string|void The string of the URL, if redirect needed.
 */
function redirect_canonical($requested_url = null, $do_redirect = true)
{
    global $wp_rewrite, $is_IIS, $wp_query, $wpdb, $wp;
    if (isset($_SERVER['REQUEST_METHOD']) && !in_array(strtoupper($_SERVER['REQUEST_METHOD']), array('GET', 'HEAD'), true)) {
        return;
    }
    /*
     * If we're not in wp-admin and the post has been published and preview nonce
     * is non-existent or invalid then no need for preview in query.
     */
    if (is_preview() && get_query_var('p') && 'publish' === get_post_status(get_query_var('p'))) {
        if (!isset($_GET['preview_id']) || !isset($_GET['preview_nonce']) || !wp_verify_nonce($_GET['preview_nonce'], 'post_preview_' . (int) $_GET['preview_id'])) {
            $wp_query->is_preview = false;
        }
    }
    if (is_admin() || is_search() || is_preview() || is_trackback() || is_favicon() || $is_IIS && !iis7_supports_permalinks()) {
        return;
    }
    if (!$requested_url && isset($_SERVER['HTTP_HOST'])) {
        // Build the URL in the address bar.
        $requested_url = is_ssl() ? 'https://' : 'http://';
        $requested_url .= $_SERVER['HTTP_HOST'];
        $requested_url .= $_SERVER['REQUEST_URI'];
    }
    $original = parse_url($requested_url);
    if (false === $original) {
        return;
    }
    $redirect = $original;
    $redirect_url = false;
    $redirect_obj = false;
    // Notice fixing.
    if (!isset($redirect['path'])) {
        $redirect['path'] = '';
    }
    if (!isset($redirect['query'])) {
        $redirect['query'] = '';
    }
    /*
     * If the original URL ended with non-breaking spaces, they were almost
     * certainly inserted by accident. Let's remove them, so the reader doesn't
     * see a 404 error with no obvious cause.
     */
    $redirect['path'] = preg_replace('|(%C2%A0)+$|i', '', $redirect['path']);
    // It's not a preview, so remove it from URL.
    if (get_query_var('preview')) {
        $redirect['query'] = remove_query_arg('preview', $redirect['query']);
    }
    $post_id = get_query_var('p');
    if (is_feed() && $post_id) {
        $redirect_url = get_post_comments_feed_link($post_id, get_query_var('feed'));
        $redirect_obj = get_post($post_id);
        if ($redirect_url) {
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type', 'feed'), $redirect_url);
            $redirect['path'] = parse_url($redirect_url, PHP_URL_PATH);
        }
    }
    if (is_singular() && $wp_query->post_count < 1 && $post_id) {
        $vars = $wpdb->get_results($wpdb->prepare("SELECT post_type, post_parent FROM {$wpdb->posts} WHERE ID = %d", $post_id));
        if (!empty($vars[0])) {
            $vars = $vars[0];
            if ('revision' === $vars->post_type && $vars->post_parent > 0) {
                $post_id = $vars->post_parent;
            }
            $redirect_url = get_permalink($post_id);
            $redirect_obj = get_post($post_id);
            if ($redirect_url) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    }
    // These tests give us a WP-generated permalink.
    if (is_404()) {
        // Redirect ?page_id, ?p=, ?attachment_id= to their respective URLs.
        $post_id = max(get_query_var('p'), get_query_var('page_id'), get_query_var('attachment_id'));
        $redirect_post = $post_id ? get_post($post_id) : false;
        if ($redirect_post) {
            $post_type_obj = get_post_type_object($redirect_post->post_type);
            if ($post_type_obj && $post_type_obj->public && 'auto-draft' !== $redirect_post->post_status) {
                $redirect_url = get_permalink($redirect_post);
                $redirect_obj = get_post($redirect_post);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
        $year = get_query_var('year');
        $month = get_query_var('monthnum');
        $day = get_query_var('day');
        if ($year && $month && $day) {
            $date = sprintf('%04d-%02d-%02d', $year, $month, $day);
            if (!wp_checkdate($month, $day, $year, $date)) {
                $redirect_url = get_month_link($year, $month);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum', 'day'), $redirect_url);
            }
        } elseif ($year && $month && $month > 12) {
            $redirect_url = get_year_link($year);
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum'), $redirect_url);
        }
        // Strip off non-existing <!--nextpage--> links from single posts or pages.
        if (get_query_var('page')) {
            $post_id = 0;
            if ($wp_query->queried_object instanceof WP_Post) {
                $post_id = $wp_query->queried_object->ID;
            } elseif ($wp_query->post) {
                $post_id = $wp_query->post->ID;
            }
            if ($post_id) {
                $redirect_url = get_permalink($post_id);
                $redirect_obj = get_post($post_id);
                $redirect['path'] = rtrim($redirect['path'], (int) get_query_var('page') . '/');
                $redirect['query'] = remove_query_arg('page', $redirect['query']);
            }
        }
        if (!$redirect_url) {
            $redirect_url = redirect_guess_404_permalink();
            if ($redirect_url) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('page', 'feed', 'p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    } elseif (is_object($wp_rewrite) && $wp_rewrite->using_permalinks()) {
        // Rewriting of old ?p=X, ?m=2004, ?m=200401, ?m=20040101.
        if (is_attachment() && !array_diff(array_keys($wp->query_vars), array('attachment', 'attachment_id')) && !$redirect_url) {
            if (!empty($_GET['attachment_id'])) {
                $redirect_url = get_attachment_link(get_query_var('attachment_id'));
                $redirect_obj = get_post(get_query_var('attachment_id'));
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('attachment_id', $redirect['query']);
                }
            } else {
                $redirect_url = get_attachment_link();
                $redirect_obj = get_post();
            }
        } elseif (is_single() && !empty($_GET['p']) && !$redirect_url) {
            $redirect_url = get_permalink(get_query_var('p'));
            $redirect_obj = get_post(get_query_var('p'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg(array('p', 'post_type'), $redirect['query']);
            }
        } elseif (is_single() && !empty($_GET['name']) && !$redirect_url) {
            $redirect_url = get_permalink($wp_query->get_queried_object_id());
            $redirect_obj = get_post($wp_query->get_queried_object_id());
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('name', $redirect['query']);
            }
        } elseif (is_page() && !empty($_GET['page_id']) && !$redirect_url) {
            $redirect_url = get_permalink(get_query_var('page_id'));
            $redirect_obj = get_post(get_query_var('page_id'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (is_page() && !is_feed() && !$redirect_url && 'page' === get_option('show_on_front') && get_queried_object_id() === (int) get_option('page_on_front')) {
            $redirect_url = home_url('/');
        } elseif (is_home() && !empty($_GET['page_id']) && !$redirect_url && 'page' === get_option('show_on_front') && get_query_var('page_id') === (int) get_option('page_for_posts')) {
            $redirect_url = get_permalink(get_option('page_for_posts'));
            $redirect_obj = get_post(get_option('page_for_posts'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (!empty($_GET['m']) && (is_year() || is_month() || is_day())) {
            $m = get_query_var('m');
            switch (strlen($m)) {
                case 4:
                    // Yearly.
                    $redirect_url = get_year_link($m);
                    break;
                case 6:
                    // Monthly.
                    $redirect_url = get_month_link(substr($m, 0, 4), substr($m, 4, 2));
                    break;
                case 8:
                    // Daily.
                    $redirect_url = get_day_link(substr($m, 0, 4), substr($m, 4, 2), substr($m, 6, 2));
                    break;
            }
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('m', $redirect['query']);
            }
            // Now moving on to non ?m=X year/month/day links.
        } elseif (is_date()) {
            $year = get_query_var('year');
            $month = get_query_var('monthnum');
            $day = get_query_var('day');
            if (is_day() && $year && $month && !empty($_GET['day'])) {
                $redirect_url = get_day_link($year, $month, $day);
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg(array('year', 'monthnum', 'day'), $redirect['query']);
                }
            } elseif (is_month() && $year && !empty($_GET['monthnum'])) {
                $redirect_url = get_month_link($year, $month);
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg(array('year', 'monthnum'), $redirect['query']);
                }
            } elseif (is_year() && !empty($_GET['year'])) {
                $redirect_url = get_year_link($year);
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('year', $redirect['query']);
                }
            }
        } elseif (is_author() && !empty($_GET['author']) && preg_match('|^[0-9]+$|', $_GET['author'])) {
            $author = get_userdata(get_query_var('author'));
            if (false !== $author && $wpdb->get_var($wpdb->prepare("SELECT ID FROM {$wpdb->posts} WHERE {$wpdb->posts}.post_author = %d AND {$wpdb->posts}.post_status = 'publish' LIMIT 1", $author->ID))) {
                $redirect_url = get_author_posts_url($author->ID, $author->user_nicename);
                $redirect_obj = $author;
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('author', $redirect['query']);
                }
            }
        } elseif (is_category() || is_tag() || is_tax()) {
            // Terms (tags/categories).
            $term_count = 0;
            foreach ($wp_query->tax_query->queried_terms as $tax_query) {
                if (isset($tax_query['terms']) && is_countable($tax_query['terms'])) {
                    $term_count += count($tax_query['terms']);
                }
            }
            $obj = $wp_query->get_queried_object();
            if ($term_count <= 1 && !empty($obj->term_id)) {
                $tax_url = get_term_link((int) $obj->term_id, $obj->taxonomy);
                if ($tax_url && !is_wp_error($tax_url)) {
                    if (!empty($redirect['query'])) {
                        // Strip taxonomy query vars off the URL.
                        $qv_remove = array('term', 'taxonomy');
                        if (is_category()) {
                            $qv_remove[] = 'category_name';
                            $qv_remove[] = 'cat';
                        } elseif (is_tag()) {
                            $qv_remove[] = 'tag';
                            $qv_remove[] = 'tag_id';
                        } else {
                            // Custom taxonomies will have a custom query var, remove those too.
                            $tax_obj = get_taxonomy($obj->taxonomy);
                            if (false !== $tax_obj->query_var) {
                                $qv_remove[] = $tax_obj->query_var;
                            }
                        }
                        $rewrite_vars = array_diff(array_keys($wp_query->query), array_keys($_GET));
                        // Check to see if all the query vars are coming from the rewrite, none are set via $_GET.
                        if (!array_diff($rewrite_vars, array_keys($_GET))) {
                            // Remove all of the per-tax query vars.
                            $redirect['query'] = remove_query_arg($qv_remove, $redirect['query']);
                            // Create the destination URL for this taxonomy.
                            $tax_url = parse_url($tax_url);
                            if (!empty($tax_url['query'])) {
                                // Taxonomy accessible via ?taxonomy=...&term=... or any custom query var.
                                parse_str($tax_url['query'], $query_vars);
                                $redirect['query'] = add_query_arg($query_vars, $redirect['query']);
                            } else {
                                // Taxonomy is accessible via a "pretty URL".
                                $redirect['path'] = $tax_url['path'];
                            }
                        } else {
                            // Some query vars are set via $_GET. Unset those from $_GET that exist via the rewrite.
                            foreach ($qv_remove as $_qv) {
                                if (isset($rewrite_vars[$_qv])) {
                                    $redirect['query'] = remove_query_arg($_qv, $redirect['query']);
                                }
                            }
                        }
                    }
                }
            }
        } elseif (is_single() && str_contains($wp_rewrite->permalink_structure, '%category%')) {
            $category_name = get_query_var('category_name');
            if ($category_name) {
                $category = get_category_by_path($category_name);
                if (!$category || is_wp_error($category) || !has_term($category->term_id, 'category', $wp_query->get_queried_object_id())) {
                    $redirect_url = get_permalink($wp_query->get_queried_object_id());
                    $redirect_obj = get_post($wp_query->get_queried_object_id());
                }
            }
        }
        // Post paging.
        if (is_singular() && get_query_var('page')) {
            $page = get_query_var('page');
            if (!$redirect_url) {
                $redirect_url = get_permalink(get_queried_object_id());
                $redirect_obj = get_post(get_queried_object_id());
            }
            if ($page > 1) {
                $redirect_url = trailingslashit($redirect_url);
                if (is_front_page()) {
                    $redirect_url .= user_trailingslashit("{$wp_rewrite->pagination_base}/{$page}", 'paged');
                } else {
                    $redirect_url .= user_trailingslashit($page, 'single_paged');
                }
            }
            $redirect['query'] = remove_query_arg('page', $redirect['query']);
        }
        if (get_query_var('sitemap')) {
            $redirect_url = get_sitemap_url(get_query_var('sitemap'), get_query_var('sitemap-subtype'), get_query_var('paged'));
            $redirect['query'] = remove_query_arg(array('sitemap', 'sitemap-subtype', 'paged'), $redirect['query']);
        } elseif (get_query_var('paged') || is_feed() || get_query_var('cpage')) {
            // Paging and feeds.
            $paged = get_query_var('paged');
            $feed = get_query_var('feed');
            $cpage = get_query_var('cpage');
            while (preg_match("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", $redirect['path']) || preg_match('#/(comments/?)?(feed|rss2?|rdf|atom)(/+)?$#', $redirect['path']) || preg_match("#/{$wp_rewrite->comments_pagination_base}-[0-9]+(/+)?\$#", $redirect['path'])) {
                // Strip off any existing paging.
                $redirect['path'] = preg_replace("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", '/', $redirect['path']);
                // Strip off feed endings.
                $redirect['path'] = preg_replace('#/(comments/?)?(feed|rss2?|rdf|atom)(/+|$)#', '/', $redirect['path']);
                // Strip off any existing comment paging.
                $redirect['path'] = preg_replace("#/{$wp_rewrite->comments_pagination_base}-[0-9]+?(/+)?\$#", '/', $redirect['path']);
            }
            $addl_path = '';
            $default_feed = get_default_feed();
            if (is_feed() && in_array($feed, $wp_rewrite->feeds, true)) {
                $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                if (!is_singular() && get_query_var('withcomments')) {
                    $addl_path .= 'comments/';
                }
                if ('rss' === $default_feed && 'feed' === $feed || 'rss' === $feed) {
                    $format = ('rss2' === $default_feed) ? '' : 'rss2';
                } else {
                    $format = ($default_feed === $feed || 'feed' === $feed) ? '' : $feed;
                }
                $addl_path .= user_trailingslashit('feed/' . $format, 'feed');
                $redirect['query'] = remove_query_arg('feed', $redirect['query']);
            } elseif (is_feed() && 'old' === $feed) {
                $old_feed_files = array('wp-atom.php' => 'atom', 'wp-commentsrss2.php' => 'comments_rss2', 'wp-feed.php' => $default_feed, 'wp-rdf.php' => 'rdf', 'wp-rss.php' => 'rss2', 'wp-rss2.php' => 'rss2');
                if (isset($old_feed_files[basename($redirect['path'])])) {
                    $redirect_url = get_feed_link($old_feed_files[basename($redirect['path'])]);
                    wp_redirect($redirect_url, 301);
                    die;
                }
            }
            if ($paged > 0) {
                $redirect['query'] = remove_query_arg('paged', $redirect['query']);
                if (!is_feed()) {
                    if (!is_single()) {
                        $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                        if ($paged > 1) {
                            $addl_path .= user_trailingslashit("{$wp_rewrite->pagination_base}/{$paged}", 'paged');
                        }
                    }
                } elseif ($paged > 1) {
                    $redirect['query'] = add_query_arg('paged', $paged, $redirect['query']);
                }
            }
            $default_comments_page = get_option('default_comments_page');
            if (get_option('page_comments') && ('newest' === $default_comments_page && $cpage > 0 || 'newest' !== $default_comments_page && $cpage > 1)) {
                $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                $addl_path .= user_trailingslashit($wp_rewrite->comments_pagination_base . '-' . $cpage, 'commentpaged');
                $redirect['query'] = remove_query_arg('cpage', $redirect['query']);
            }
            // Strip off trailing /index.php/.
            $redirect['path'] = preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/?$|', '/', $redirect['path']);
            $redirect['path'] = user_trailingslashit($redirect['path']);
            if (!empty($addl_path) && $wp_rewrite->using_index_permalinks() && !str_contains($redirect['path'], '/' . $wp_rewrite->index . '/')) {
                $redirect['path'] = trailingslashit($redirect['path']) . $wp_rewrite->index . '/';
            }
            if (!empty($addl_path)) {
                $redirect['path'] = trailingslashit($redirect['path']) . $addl_path;
            }
            $redirect_url = $redirect['scheme'] . '://' . $redirect['host'] . $redirect['path'];
        }
        if ('wp-register.php' === basename($redirect['path'])) {
            if (is_multisite()) {
                /** This filter is documented in wp-login.php */
                $redirect_url = apply_filters('wp_signup_location', network_site_url('wp-signup.php'));
            } else {
                $redirect_url = wp_registration_url();
            }
            wp_redirect($redirect_url, 301);
            die;
        }
    }
    $is_attachment_redirect = false;
    if (is_attachment() && !get_option('wp_attachment_pages_enabled')) {
        $attachment_id = get_query_var('attachment_id');
        $attachment_post = get_post($attachment_id);
        $attachment_parent_id = $attachment_post ? $attachment_post->post_parent : 0;
        $attachment_url = wp_get_attachment_url($attachment_id);
        if ($attachment_url !== $redirect_url) {
            /*
             * If an attachment is attached to a post, it inherits the parent post's status. Fetch the
             * parent post to check its status later.
             */
            if ($attachment_parent_id) {
                $redirect_obj = get_post($attachment_parent_id);
            }
            $redirect_url = $attachment_url;
        }
        $is_attachment_redirect = true;
    }
    $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    // Tack on any additional query vars.
    if ($redirect_url && !empty($redirect['query'])) {
        parse_str($redirect['query'], $_parsed_query);
        $redirect = parse_url($redirect_url);
        if (!empty($_parsed_query['name']) && !empty($redirect['query'])) {
            parse_str($redirect['query'], $_parsed_redirect_query);
            if (empty($_parsed_redirect_query['name'])) {
                unset($_parsed_query['name']);
            }
        }
        $_parsed_query = array_combine(rawurlencode_deep(array_keys($_parsed_query)), rawurlencode_deep(array_values($_parsed_query)));
        $redirect_url = add_query_arg($_parsed_query, $redirect_url);
    }
    if ($redirect_url) {
        $redirect = parse_url($redirect_url);
    }
    // www.example.com vs. example.com
    $user_home = parse_url(home_url());
    if (!empty($user_home['host'])) {
        $redirect['host'] = $user_home['host'];
    }
    if (empty($user_home['path'])) {
        $user_home['path'] = '/';
    }
    // Handle ports.
    if (!empty($user_home['port'])) {
        $redirect['port'] = $user_home['port'];
    } else {
        unset($redirect['port']);
    }
    // Trailing /index.php.
    $redirect['path'] = preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/*?$|', '/', $redirect['path']);
    $punctuation_pattern = implode('|', array_map('preg_quote', array(
        ' ',
        '%20',
        // Space.
        '!',
        '%21',
        // Exclamation mark.
        '"',
        '%22',
        // Double quote.
        "'",
        '%27',
        // Single quote.
        '(',
        '%28',
        // Opening bracket.
        ')',
        '%29',
        // Closing bracket.
        ',',
        '%2C',
        // Comma.
        '.',
        '%2E',
        // Period.
        ';',
        '%3B',
        // Semicolon.
        '{',
        '%7B',
        // Opening curly bracket.
        '}',
        '%7D',
        // Closing curly bracket.
        '%E2%80%9C',
        // Opening curly quote.
        '%E2%80%9D',
    )));
    // Remove trailing spaces and end punctuation from the path.
    $redirect['path'] = preg_replace("#({$punctuation_pattern})+\$#", '', $redirect['path']);
    if (!empty($redirect['query'])) {
        // Remove trailing spaces and end punctuation from certain terminating query string args.
        $redirect['query'] = preg_replace("#((^|&)(p|page_id|cat|tag)=[^&]*?)({$punctuation_pattern})+\$#", '$1', $redirect['query']);
        // Clean up empty query strings.
        $redirect['query'] = trim(preg_replace('#(^|&)(p|page_id|cat|tag)=?(&|$)#', '&', $redirect['query']), '&');
        // Redirect obsolete feeds.
        $redirect['query'] = preg_replace('#(^|&)feed=rss(&|$)#', '$1feed=rss2$2', $redirect['query']);
        // Remove redundant leading ampersands.
        $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    }
    // Strip /index.php/ when we're not using PATHINFO permalinks.
    if (!$wp_rewrite->using_index_permalinks()) {
        $redirect['path'] = str_replace('/' . $wp_rewrite->index . '/', '/', $redirect['path']);
    }
    // Trailing slashes.
    if (is_object($wp_rewrite) && $wp_rewrite->using_permalinks() && !$is_attachment_redirect && !is_404() && (!is_front_page() || is_front_page() && get_query_var('paged') > 1)) {
        $user_ts_type = '';
        if (get_query_var('paged') > 0) {
            $user_ts_type = 'paged';
        } else {
            foreach (array('single', 'category', 'page', 'day', 'month', 'year', 'home') as $type) {
                $func = 'is_' . $type;
                if (call_user_func($func)) {
                    $user_ts_type = $type;
                    break;
                }
            }
        }
        $redirect['path'] = user_trailingslashit($redirect['path'], $user_ts_type);
    } elseif (is_front_page()) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Remove trailing slash for robots.txt or sitemap requests.
    if (is_robots() || !empty(get_query_var('sitemap')) || !empty(get_query_var('sitemap-stylesheet'))) {
        $redirect['path'] = untrailingslashit($redirect['path']);
    }
    // Strip multiple slashes out of the URL.
    if (str_contains($redirect['path'], '//')) {
        $redirect['path'] = preg_replace('|/+|', '/', $redirect['path']);
    }
    // Always trailing slash the Front Page URL.
    if (trailingslashit($redirect['path']) === trailingslashit($user_home['path'])) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    $original_host_low = strtolower($original['host']);
    $redirect_host_low = strtolower($redirect['host']);
    /*
     * Ignore differences in host capitalization, as this can lead to infinite redirects.
     * Only redirect no-www <=> yes-www.
     */
    if ($original_host_low === $redirect_host_low || 'www.' . $original_host_low !== $redirect_host_low && 'www.' . $redirect_host_low !== $original_host_low) {
        $redirect['host'] = $original['host'];
    }
    $compare_original = array($original['host'], $original['path']);
    if (!empty($original['port'])) {
        $compare_original[] = $original['port'];
    }
    if (!empty($original['query'])) {
        $compare_original[] = $original['query'];
    }
    $compare_redirect = array($redirect['host'], $redirect['path']);
    if (!empty($redirect['port'])) {
        $compare_redirect[] = $redirect['port'];
    }
    if (!empty($redirect['query'])) {
        $compare_redirect[] = $redirect['query'];
    }
    if ($compare_original !== $compare_redirect) {
        $redirect_url = $redirect['scheme'] . '://' . $redirect['host'];
        if (!empty($redirect['port'])) {
            $redirect_url .= ':' . $redirect['port'];
        }
        $redirect_url .= $redirect['path'];
        if (!empty($redirect['query'])) {
            $redirect_url .= '?' . $redirect['query'];
        }
    }
    if (!$redirect_url || $redirect_url === $requested_url) {
        return;
    }
    // Hex-encoded octets are case-insensitive.
    if (str_contains($requested_url, '%')) {
        if (!function_exists('lowercase_octets')) {
            /**
             * Converts the first hex-encoded octet match to lowercase.
             *
             * @since 3.1.0
             * @ignore
             *
             * @param array $matches Hex-encoded octet matches for the requested URL.
             * @return string Lowercased version of the first match.
             */
            function lowercase_octets($matches)
            {
                return strtolower($matches[0]);
            }
        }
        $requested_url = preg_replace_callback('|%[a-fA-F0-9][a-fA-F0-9]|', 'lowercase_octets', $requested_url);
    }
    if ($redirect_obj instanceof WP_Post) {
        $post_status_obj = get_post_status_object(get_post_status($redirect_obj));
        /*
         * Unset the redirect object and URL if they are not readable by the user.
         * This condition is a little confusing as the condition needs to pass if
         * the post is not readable by the user. That's why there are ! (not) conditions
         * throughout.
         */
        if (!($post_status_obj->private && current_user_can('read_post', $redirect_obj->ID)) && !is_post_publicly_viewable($redirect_obj)) {
            $redirect_obj = false;
            $redirect_url = false;
        }
    }
    /**
     * Filters the canonical redirect URL.
     *
     * Returning false to this filter will cancel the redirect.
     *
     * @since 2.3.0
     *
     * @param string $redirect_url  The redirect URL.
     * @param string $requested_url The requested URL.
     */
    $redirect_url = apply_filters('redirect_canonical', $redirect_url, $requested_url);
    // Yes, again -- in case the filter aborted the request.
    if (!$redirect_url || strip_fragment_from_url($redirect_url) === strip_fragment_from_url($requested_url)) {
        return;
    }
    if ($do_redirect) {
        // Protect against chained redirects.
        if (!redirect_canonical($redirect_url, false)) {
            wp_redirect($redirect_url, 301);
            exit;
        } else {
            // Debug.
            // die("1: $redirect_url<br />2: " . redirect_canonical( $redirect_url, false ) );
            return;
        }
    } else {
        return $redirect_url;
    }
}

WordPress Version: 6.4

/**
 * Canonical API to handle WordPress Redirecting
 *
 * Based on "Permalink Redirect" from Scott Yang and "Enforce www. Preference"
 * by Mark Jaquith
 *
 * @package WordPress
 * @since 2.3.0
 */
/**
 * Redirects incoming links to the proper URL based on the site url.
 *
 * Search engines consider www.somedomain.com and somedomain.com to be two
 * different URLs when they both go to the same location. This SEO enhancement
 * prevents penalty for duplicate content by redirecting all incoming links to
 * one or the other.
 *
 * Prevents redirection for feeds, trackbacks, searches, and
 * admin URLs. Does not redirect on non-pretty-permalink-supporting IIS 7+,
 * page/post previews, WP admin, Trackbacks, robots.txt, favicon.ico, searches,
 * or on POST requests.
 *
 * Will also attempt to find the correct link when a user enters a URL that does
 * not exist based on exact WordPress query. Will instead try to parse the URL
 * or query in an attempt to figure the correct page to go to.
 *
 * @since 2.3.0
 *
 * @global WP_Rewrite $wp_rewrite WordPress rewrite component.
 * @global bool       $is_IIS
 * @global WP_Query   $wp_query   WordPress Query object.
 * @global wpdb       $wpdb       WordPress database abstraction object.
 * @global WP         $wp         Current WordPress environment instance.
 *
 * @param string $requested_url Optional. The URL that was requested, used to
 *                              figure if redirect is needed.
 * @param bool   $do_redirect   Optional. Redirect to the new URL.
 * @return string|void The string of the URL, if redirect needed.
 */
function redirect_canonical($requested_url = null, $do_redirect = true)
{
    global $wp_rewrite, $is_IIS, $wp_query, $wpdb, $wp;
    if (isset($_SERVER['REQUEST_METHOD']) && !in_array(strtoupper($_SERVER['REQUEST_METHOD']), array('GET', 'HEAD'), true)) {
        return;
    }
    /*
     * If we're not in wp-admin and the post has been published and preview nonce
     * is non-existent or invalid then no need for preview in query.
     */
    if (is_preview() && get_query_var('p') && 'publish' === get_post_status(get_query_var('p'))) {
        if (!isset($_GET['preview_id']) || !isset($_GET['preview_nonce']) || !wp_verify_nonce($_GET['preview_nonce'], 'post_preview_' . (int) $_GET['preview_id'])) {
            $wp_query->is_preview = false;
        }
    }
    if (is_admin() || is_search() || is_preview() || is_trackback() || is_favicon() || $is_IIS && !iis7_supports_permalinks()) {
        return;
    }
    if (!$requested_url && isset($_SERVER['HTTP_HOST'])) {
        // Build the URL in the address bar.
        $requested_url = is_ssl() ? 'https://' : 'http://';
        $requested_url .= $_SERVER['HTTP_HOST'];
        $requested_url .= $_SERVER['REQUEST_URI'];
    }
    $original = parse_url($requested_url);
    if (false === $original) {
        return;
    }
    $redirect = $original;
    $redirect_url = false;
    $redirect_obj = false;
    // Notice fixing.
    if (!isset($redirect['path'])) {
        $redirect['path'] = '';
    }
    if (!isset($redirect['query'])) {
        $redirect['query'] = '';
    }
    /*
     * If the original URL ended with non-breaking spaces, they were almost
     * certainly inserted by accident. Let's remove them, so the reader doesn't
     * see a 404 error with no obvious cause.
     */
    $redirect['path'] = preg_replace('|(%C2%A0)+$|i', '', $redirect['path']);
    // It's not a preview, so remove it from URL.
    if (get_query_var('preview')) {
        $redirect['query'] = remove_query_arg('preview', $redirect['query']);
    }
    $post_id = get_query_var('p');
    if (is_feed() && $post_id) {
        $redirect_url = get_post_comments_feed_link($post_id, get_query_var('feed'));
        $redirect_obj = get_post($post_id);
        if ($redirect_url) {
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type', 'feed'), $redirect_url);
            $redirect['path'] = parse_url($redirect_url, PHP_URL_PATH);
        }
    }
    if (is_singular() && $wp_query->post_count < 1 && $post_id) {
        $vars = $wpdb->get_results($wpdb->prepare("SELECT post_type, post_parent FROM {$wpdb->posts} WHERE ID = %d", $post_id));
        if (!empty($vars[0])) {
            $vars = $vars[0];
            if ('revision' === $vars->post_type && $vars->post_parent > 0) {
                $post_id = $vars->post_parent;
            }
            $redirect_url = get_permalink($post_id);
            $redirect_obj = get_post($post_id);
            if ($redirect_url) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    }
    // These tests give us a WP-generated permalink.
    if (is_404()) {
        // Redirect ?page_id, ?p=, ?attachment_id= to their respective URLs.
        $post_id = max(get_query_var('p'), get_query_var('page_id'), get_query_var('attachment_id'));
        $redirect_post = $post_id ? get_post($post_id) : false;
        if ($redirect_post) {
            $post_type_obj = get_post_type_object($redirect_post->post_type);
            if ($post_type_obj && $post_type_obj->public && 'auto-draft' !== $redirect_post->post_status) {
                $redirect_url = get_permalink($redirect_post);
                $redirect_obj = get_post($redirect_post);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
        $year = get_query_var('year');
        $month = get_query_var('monthnum');
        $day = get_query_var('day');
        if ($year && $month && $day) {
            $date = sprintf('%04d-%02d-%02d', $year, $month, $day);
            if (!wp_checkdate($month, $day, $year, $date)) {
                $redirect_url = get_month_link($year, $month);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum', 'day'), $redirect_url);
            }
        } elseif ($year && $month && $month > 12) {
            $redirect_url = get_year_link($year);
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum'), $redirect_url);
        }
        // Strip off non-existing <!--nextpage--> links from single posts or pages.
        if (get_query_var('page')) {
            $post_id = 0;
            if ($wp_query->queried_object instanceof WP_Post) {
                $post_id = $wp_query->queried_object->ID;
            } elseif ($wp_query->post) {
                $post_id = $wp_query->post->ID;
            }
            if ($post_id) {
                $redirect_url = get_permalink($post_id);
                $redirect_obj = get_post($post_id);
                $redirect['path'] = rtrim($redirect['path'], (int) get_query_var('page') . '/');
                $redirect['query'] = remove_query_arg('page', $redirect['query']);
            }
        }
        if (!$redirect_url) {
            $redirect_url = redirect_guess_404_permalink();
            if ($redirect_url) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('page', 'feed', 'p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    } elseif (is_object($wp_rewrite) && $wp_rewrite->using_permalinks()) {
        // Rewriting of old ?p=X, ?m=2004, ?m=200401, ?m=20040101.
        if (is_attachment() && !array_diff(array_keys($wp->query_vars), array('attachment', 'attachment_id')) && !$redirect_url) {
            if (!empty($_GET['attachment_id'])) {
                $redirect_url = get_attachment_link(get_query_var('attachment_id'));
                $redirect_obj = get_post(get_query_var('attachment_id'));
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('attachment_id', $redirect['query']);
                }
            } else {
                $redirect_url = get_attachment_link();
                $redirect_obj = get_post();
            }
        } elseif (is_single() && !empty($_GET['p']) && !$redirect_url) {
            $redirect_url = get_permalink(get_query_var('p'));
            $redirect_obj = get_post(get_query_var('p'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg(array('p', 'post_type'), $redirect['query']);
            }
        } elseif (is_single() && !empty($_GET['name']) && !$redirect_url) {
            $redirect_url = get_permalink($wp_query->get_queried_object_id());
            $redirect_obj = get_post($wp_query->get_queried_object_id());
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('name', $redirect['query']);
            }
        } elseif (is_page() && !empty($_GET['page_id']) && !$redirect_url) {
            $redirect_url = get_permalink(get_query_var('page_id'));
            $redirect_obj = get_post(get_query_var('page_id'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (is_page() && !is_feed() && !$redirect_url && 'page' === get_option('show_on_front') && get_queried_object_id() === (int) get_option('page_on_front')) {
            $redirect_url = home_url('/');
        } elseif (is_home() && !empty($_GET['page_id']) && !$redirect_url && 'page' === get_option('show_on_front') && get_query_var('page_id') === (int) get_option('page_for_posts')) {
            $redirect_url = get_permalink(get_option('page_for_posts'));
            $redirect_obj = get_post(get_option('page_for_posts'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (!empty($_GET['m']) && (is_year() || is_month() || is_day())) {
            $m = get_query_var('m');
            switch (strlen($m)) {
                case 4:
                    // Yearly.
                    $redirect_url = get_year_link($m);
                    break;
                case 6:
                    // Monthly.
                    $redirect_url = get_month_link(substr($m, 0, 4), substr($m, 4, 2));
                    break;
                case 8:
                    // Daily.
                    $redirect_url = get_day_link(substr($m, 0, 4), substr($m, 4, 2), substr($m, 6, 2));
                    break;
            }
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('m', $redirect['query']);
            }
            // Now moving on to non ?m=X year/month/day links.
        } elseif (is_date()) {
            $year = get_query_var('year');
            $month = get_query_var('monthnum');
            $day = get_query_var('day');
            if (is_day() && $year && $month && !empty($_GET['day'])) {
                $redirect_url = get_day_link($year, $month, $day);
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg(array('year', 'monthnum', 'day'), $redirect['query']);
                }
            } elseif (is_month() && $year && !empty($_GET['monthnum'])) {
                $redirect_url = get_month_link($year, $month);
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg(array('year', 'monthnum'), $redirect['query']);
                }
            } elseif (is_year() && !empty($_GET['year'])) {
                $redirect_url = get_year_link($year);
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('year', $redirect['query']);
                }
            }
        } elseif (is_author() && !empty($_GET['author']) && preg_match('|^[0-9]+$|', $_GET['author'])) {
            $author = get_userdata(get_query_var('author'));
            if (false !== $author && $wpdb->get_var($wpdb->prepare("SELECT ID FROM {$wpdb->posts} WHERE {$wpdb->posts}.post_author = %d AND {$wpdb->posts}.post_status = 'publish' LIMIT 1", $author->ID))) {
                $redirect_url = get_author_posts_url($author->ID, $author->user_nicename);
                $redirect_obj = $author;
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('author', $redirect['query']);
                }
            }
        } elseif (is_category() || is_tag() || is_tax()) {
            // Terms (tags/categories).
            $term_count = 0;
            foreach ($wp_query->tax_query->queried_terms as $tax_query) {
                if (isset($tax_query['terms']) && is_countable($tax_query['terms'])) {
                    $term_count += count($tax_query['terms']);
                }
            }
            $obj = $wp_query->get_queried_object();
            if ($term_count <= 1 && !empty($obj->term_id)) {
                $tax_url = get_term_link((int) $obj->term_id, $obj->taxonomy);
                if ($tax_url && !is_wp_error($tax_url)) {
                    if (!empty($redirect['query'])) {
                        // Strip taxonomy query vars off the URL.
                        $qv_remove = array('term', 'taxonomy');
                        if (is_category()) {
                            $qv_remove[] = 'category_name';
                            $qv_remove[] = 'cat';
                        } elseif (is_tag()) {
                            $qv_remove[] = 'tag';
                            $qv_remove[] = 'tag_id';
                        } else {
                            // Custom taxonomies will have a custom query var, remove those too.
                            $tax_obj = get_taxonomy($obj->taxonomy);
                            if (false !== $tax_obj->query_var) {
                                $qv_remove[] = $tax_obj->query_var;
                            }
                        }
                        $rewrite_vars = array_diff(array_keys($wp_query->query), array_keys($_GET));
                        // Check to see if all the query vars are coming from the rewrite, none are set via $_GET.
                        if (!array_diff($rewrite_vars, array_keys($_GET))) {
                            // Remove all of the per-tax query vars.
                            $redirect['query'] = remove_query_arg($qv_remove, $redirect['query']);
                            // Create the destination URL for this taxonomy.
                            $tax_url = parse_url($tax_url);
                            if (!empty($tax_url['query'])) {
                                // Taxonomy accessible via ?taxonomy=...&term=... or any custom query var.
                                parse_str($tax_url['query'], $query_vars);
                                $redirect['query'] = add_query_arg($query_vars, $redirect['query']);
                            } else {
                                // Taxonomy is accessible via a "pretty URL".
                                $redirect['path'] = $tax_url['path'];
                            }
                        } else {
                            // Some query vars are set via $_GET. Unset those from $_GET that exist via the rewrite.
                            foreach ($qv_remove as $_qv) {
                                if (isset($rewrite_vars[$_qv])) {
                                    $redirect['query'] = remove_query_arg($_qv, $redirect['query']);
                                }
                            }
                        }
                    }
                }
            }
        } elseif (is_single() && str_contains($wp_rewrite->permalink_structure, '%category%')) {
            $category_name = get_query_var('category_name');
            if ($category_name) {
                $category = get_category_by_path($category_name);
                if (!$category || is_wp_error($category) || !has_term($category->term_id, 'category', $wp_query->get_queried_object_id())) {
                    $redirect_url = get_permalink($wp_query->get_queried_object_id());
                    $redirect_obj = get_post($wp_query->get_queried_object_id());
                }
            }
        }
        // Post paging.
        if (is_singular() && get_query_var('page')) {
            $page = get_query_var('page');
            if (!$redirect_url) {
                $redirect_url = get_permalink(get_queried_object_id());
                $redirect_obj = get_post(get_queried_object_id());
            }
            if ($page > 1) {
                $redirect_url = trailingslashit($redirect_url);
                if (is_front_page()) {
                    $redirect_url .= user_trailingslashit("{$wp_rewrite->pagination_base}/{$page}", 'paged');
                } else {
                    $redirect_url .= user_trailingslashit($page, 'single_paged');
                }
            }
            $redirect['query'] = remove_query_arg('page', $redirect['query']);
        }
        if (get_query_var('sitemap')) {
            $redirect_url = get_sitemap_url(get_query_var('sitemap'), get_query_var('sitemap-subtype'), get_query_var('paged'));
            $redirect['query'] = remove_query_arg(array('sitemap', 'sitemap-subtype', 'paged'), $redirect['query']);
        } elseif (get_query_var('paged') || is_feed() || get_query_var('cpage')) {
            // Paging and feeds.
            $paged = get_query_var('paged');
            $feed = get_query_var('feed');
            $cpage = get_query_var('cpage');
            while (preg_match("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", $redirect['path']) || preg_match('#/(comments/?)?(feed|rss2?|rdf|atom)(/+)?$#', $redirect['path']) || preg_match("#/{$wp_rewrite->comments_pagination_base}-[0-9]+(/+)?\$#", $redirect['path'])) {
                // Strip off any existing paging.
                $redirect['path'] = preg_replace("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", '/', $redirect['path']);
                // Strip off feed endings.
                $redirect['path'] = preg_replace('#/(comments/?)?(feed|rss2?|rdf|atom)(/+|$)#', '/', $redirect['path']);
                // Strip off any existing comment paging.
                $redirect['path'] = preg_replace("#/{$wp_rewrite->comments_pagination_base}-[0-9]+?(/+)?\$#", '/', $redirect['path']);
            }
            $addl_path = '';
            $default_feed = get_default_feed();
            if (is_feed() && in_array($feed, $wp_rewrite->feeds, true)) {
                $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                if (!is_singular() && get_query_var('withcomments')) {
                    $addl_path .= 'comments/';
                }
                if ('rss' === $default_feed && 'feed' === $feed || 'rss' === $feed) {
                    $format = ('rss2' === $default_feed) ? '' : 'rss2';
                } else {
                    $format = ($default_feed === $feed || 'feed' === $feed) ? '' : $feed;
                }
                $addl_path .= user_trailingslashit('feed/' . $format, 'feed');
                $redirect['query'] = remove_query_arg('feed', $redirect['query']);
            } elseif (is_feed() && 'old' === $feed) {
                $old_feed_files = array('wp-atom.php' => 'atom', 'wp-commentsrss2.php' => 'comments_rss2', 'wp-feed.php' => $default_feed, 'wp-rdf.php' => 'rdf', 'wp-rss.php' => 'rss2', 'wp-rss2.php' => 'rss2');
                if (isset($old_feed_files[basename($redirect['path'])])) {
                    $redirect_url = get_feed_link($old_feed_files[basename($redirect['path'])]);
                    wp_redirect($redirect_url, 301);
                    die;
                }
            }
            if ($paged > 0) {
                $redirect['query'] = remove_query_arg('paged', $redirect['query']);
                if (!is_feed()) {
                    if (!is_single()) {
                        $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                        if ($paged > 1) {
                            $addl_path .= user_trailingslashit("{$wp_rewrite->pagination_base}/{$paged}", 'paged');
                        }
                    }
                } elseif ($paged > 1) {
                    $redirect['query'] = add_query_arg('paged', $paged, $redirect['query']);
                }
            }
            $default_comments_page = get_option('default_comments_page');
            if (get_option('page_comments') && ('newest' === $default_comments_page && $cpage > 0 || 'newest' !== $default_comments_page && $cpage > 1)) {
                $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                $addl_path .= user_trailingslashit($wp_rewrite->comments_pagination_base . '-' . $cpage, 'commentpaged');
                $redirect['query'] = remove_query_arg('cpage', $redirect['query']);
            }
            // Strip off trailing /index.php/.
            $redirect['path'] = preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/?$|', '/', $redirect['path']);
            $redirect['path'] = user_trailingslashit($redirect['path']);
            if (!empty($addl_path) && $wp_rewrite->using_index_permalinks() && !str_contains($redirect['path'], '/' . $wp_rewrite->index . '/')) {
                $redirect['path'] = trailingslashit($redirect['path']) . $wp_rewrite->index . '/';
            }
            if (!empty($addl_path)) {
                $redirect['path'] = trailingslashit($redirect['path']) . $addl_path;
            }
            $redirect_url = $redirect['scheme'] . '://' . $redirect['host'] . $redirect['path'];
        }
        if ('wp-register.php' === basename($redirect['path'])) {
            if (is_multisite()) {
                /** This filter is documented in wp-login.php */
                $redirect_url = apply_filters('wp_signup_location', network_site_url('wp-signup.php'));
            } else {
                $redirect_url = wp_registration_url();
            }
            wp_redirect($redirect_url, 301);
            die;
        }
    }
    $is_attachment_redirect = false;
    if (is_attachment() && !get_option('wp_attachment_pages_enabled')) {
        $attachment_id = get_query_var('attachment_id');
        if (current_user_can('read_post', $attachment_id)) {
            $redirect_url = wp_get_attachment_url($attachment_id);
            $is_attachment_redirect = true;
        }
    }
    $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    // Tack on any additional query vars.
    if ($redirect_url && !empty($redirect['query'])) {
        parse_str($redirect['query'], $_parsed_query);
        $redirect = parse_url($redirect_url);
        if (!empty($_parsed_query['name']) && !empty($redirect['query'])) {
            parse_str($redirect['query'], $_parsed_redirect_query);
            if (empty($_parsed_redirect_query['name'])) {
                unset($_parsed_query['name']);
            }
        }
        $_parsed_query = array_combine(rawurlencode_deep(array_keys($_parsed_query)), rawurlencode_deep(array_values($_parsed_query)));
        $redirect_url = add_query_arg($_parsed_query, $redirect_url);
    }
    if ($redirect_url) {
        $redirect = parse_url($redirect_url);
    }
    // www.example.com vs. example.com
    $user_home = parse_url(home_url());
    if (!empty($user_home['host'])) {
        $redirect['host'] = $user_home['host'];
    }
    if (empty($user_home['path'])) {
        $user_home['path'] = '/';
    }
    // Handle ports.
    if (!empty($user_home['port'])) {
        $redirect['port'] = $user_home['port'];
    } else {
        unset($redirect['port']);
    }
    // Trailing /index.php.
    $redirect['path'] = preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/*?$|', '/', $redirect['path']);
    $punctuation_pattern = implode('|', array_map('preg_quote', array(
        ' ',
        '%20',
        // Space.
        '!',
        '%21',
        // Exclamation mark.
        '"',
        '%22',
        // Double quote.
        "'",
        '%27',
        // Single quote.
        '(',
        '%28',
        // Opening bracket.
        ')',
        '%29',
        // Closing bracket.
        ',',
        '%2C',
        // Comma.
        '.',
        '%2E',
        // Period.
        ';',
        '%3B',
        // Semicolon.
        '{',
        '%7B',
        // Opening curly bracket.
        '}',
        '%7D',
        // Closing curly bracket.
        '%E2%80%9C',
        // Opening curly quote.
        '%E2%80%9D',
    )));
    // Remove trailing spaces and end punctuation from the path.
    $redirect['path'] = preg_replace("#({$punctuation_pattern})+\$#", '', $redirect['path']);
    if (!empty($redirect['query'])) {
        // Remove trailing spaces and end punctuation from certain terminating query string args.
        $redirect['query'] = preg_replace("#((^|&)(p|page_id|cat|tag)=[^&]*?)({$punctuation_pattern})+\$#", '$1', $redirect['query']);
        // Clean up empty query strings.
        $redirect['query'] = trim(preg_replace('#(^|&)(p|page_id|cat|tag)=?(&|$)#', '&', $redirect['query']), '&');
        // Redirect obsolete feeds.
        $redirect['query'] = preg_replace('#(^|&)feed=rss(&|$)#', '$1feed=rss2$2', $redirect['query']);
        // Remove redundant leading ampersands.
        $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    }
    // Strip /index.php/ when we're not using PATHINFO permalinks.
    if (!$wp_rewrite->using_index_permalinks()) {
        $redirect['path'] = str_replace('/' . $wp_rewrite->index . '/', '/', $redirect['path']);
    }
    // Trailing slashes.
    if (is_object($wp_rewrite) && $wp_rewrite->using_permalinks() && !$is_attachment_redirect && !is_404() && (!is_front_page() || is_front_page() && get_query_var('paged') > 1)) {
        $user_ts_type = '';
        if (get_query_var('paged') > 0) {
            $user_ts_type = 'paged';
        } else {
            foreach (array('single', 'category', 'page', 'day', 'month', 'year', 'home') as $type) {
                $func = 'is_' . $type;
                if (call_user_func($func)) {
                    $user_ts_type = $type;
                    break;
                }
            }
        }
        $redirect['path'] = user_trailingslashit($redirect['path'], $user_ts_type);
    } elseif (is_front_page()) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Remove trailing slash for robots.txt or sitemap requests.
    if (is_robots() || !empty(get_query_var('sitemap')) || !empty(get_query_var('sitemap-stylesheet'))) {
        $redirect['path'] = untrailingslashit($redirect['path']);
    }
    // Strip multiple slashes out of the URL.
    if (str_contains($redirect['path'], '//')) {
        $redirect['path'] = preg_replace('|/+|', '/', $redirect['path']);
    }
    // Always trailing slash the Front Page URL.
    if (trailingslashit($redirect['path']) === trailingslashit($user_home['path'])) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    $original_host_low = strtolower($original['host']);
    $redirect_host_low = strtolower($redirect['host']);
    /*
     * Ignore differences in host capitalization, as this can lead to infinite redirects.
     * Only redirect no-www <=> yes-www.
     */
    if ($original_host_low === $redirect_host_low || 'www.' . $original_host_low !== $redirect_host_low && 'www.' . $redirect_host_low !== $original_host_low) {
        $redirect['host'] = $original['host'];
    }
    $compare_original = array($original['host'], $original['path']);
    if (!empty($original['port'])) {
        $compare_original[] = $original['port'];
    }
    if (!empty($original['query'])) {
        $compare_original[] = $original['query'];
    }
    $compare_redirect = array($redirect['host'], $redirect['path']);
    if (!empty($redirect['port'])) {
        $compare_redirect[] = $redirect['port'];
    }
    if (!empty($redirect['query'])) {
        $compare_redirect[] = $redirect['query'];
    }
    if ($compare_original !== $compare_redirect) {
        $redirect_url = $redirect['scheme'] . '://' . $redirect['host'];
        if (!empty($redirect['port'])) {
            $redirect_url .= ':' . $redirect['port'];
        }
        $redirect_url .= $redirect['path'];
        if (!empty($redirect['query'])) {
            $redirect_url .= '?' . $redirect['query'];
        }
    }
    if (!$redirect_url || $redirect_url === $requested_url) {
        return;
    }
    // Hex-encoded octets are case-insensitive.
    if (str_contains($requested_url, '%')) {
        if (!function_exists('lowercase_octets')) {
            /**
             * Converts the first hex-encoded octet match to lowercase.
             *
             * @since 3.1.0
             * @ignore
             *
             * @param array $matches Hex-encoded octet matches for the requested URL.
             * @return string Lowercased version of the first match.
             */
            function lowercase_octets($matches)
            {
                return strtolower($matches[0]);
            }
        }
        $requested_url = preg_replace_callback('|%[a-fA-F0-9][a-fA-F0-9]|', 'lowercase_octets', $requested_url);
    }
    if ($redirect_obj instanceof WP_Post) {
        $post_status_obj = get_post_status_object(get_post_status($redirect_obj));
        /*
         * Unset the redirect object and URL if they are not readable by the user.
         * This condition is a little confusing as the condition needs to pass if
         * the post is not readable by the user. That's why there are ! (not) conditions
         * throughout.
         */
        if (!($post_status_obj->private && current_user_can('read_post', $redirect_obj->ID)) && !is_post_publicly_viewable($redirect_obj)) {
            $redirect_obj = false;
            $redirect_url = false;
        }
    }
    /**
     * Filters the canonical redirect URL.
     *
     * Returning false to this filter will cancel the redirect.
     *
     * @since 2.3.0
     *
     * @param string $redirect_url  The redirect URL.
     * @param string $requested_url The requested URL.
     */
    $redirect_url = apply_filters('redirect_canonical', $redirect_url, $requested_url);
    // Yes, again -- in case the filter aborted the request.
    if (!$redirect_url || strip_fragment_from_url($redirect_url) === strip_fragment_from_url($requested_url)) {
        return;
    }
    if ($do_redirect) {
        // Protect against chained redirects.
        if (!redirect_canonical($redirect_url, false)) {
            wp_redirect($redirect_url, 301);
            exit;
        } else {
            // Debug.
            // die("1: $redirect_url<br />2: " . redirect_canonical( $redirect_url, false ) );
            return;
        }
    } else {
        return $redirect_url;
    }
}

WordPress Version: 6.3

/**
 * Canonical API to handle WordPress Redirecting
 *
 * Based on "Permalink Redirect" from Scott Yang and "Enforce www. Preference"
 * by Mark Jaquith
 *
 * @package WordPress
 * @since 2.3.0
 */
/**
 * Redirects incoming links to the proper URL based on the site url.
 *
 * Search engines consider www.somedomain.com and somedomain.com to be two
 * different URLs when they both go to the same location. This SEO enhancement
 * prevents penalty for duplicate content by redirecting all incoming links to
 * one or the other.
 *
 * Prevents redirection for feeds, trackbacks, searches, and
 * admin URLs. Does not redirect on non-pretty-permalink-supporting IIS 7+,
 * page/post previews, WP admin, Trackbacks, robots.txt, favicon.ico, searches,
 * or on POST requests.
 *
 * Will also attempt to find the correct link when a user enters a URL that does
 * not exist based on exact WordPress query. Will instead try to parse the URL
 * or query in an attempt to figure the correct page to go to.
 *
 * @since 2.3.0
 *
 * @global WP_Rewrite $wp_rewrite WordPress rewrite component.
 * @global bool       $is_IIS
 * @global WP_Query   $wp_query   WordPress Query object.
 * @global wpdb       $wpdb       WordPress database abstraction object.
 * @global WP         $wp         Current WordPress environment instance.
 *
 * @param string $requested_url Optional. The URL that was requested, used to
 *                              figure if redirect is needed.
 * @param bool   $do_redirect   Optional. Redirect to the new URL.
 * @return string|void The string of the URL, if redirect needed.
 */
function redirect_canonical($requested_url = null, $do_redirect = true)
{
    global $wp_rewrite, $is_IIS, $wp_query, $wpdb, $wp;
    if (isset($_SERVER['REQUEST_METHOD']) && !in_array(strtoupper($_SERVER['REQUEST_METHOD']), array('GET', 'HEAD'), true)) {
        return;
    }
    /*
     * If we're not in wp-admin and the post has been published and preview nonce
     * is non-existent or invalid then no need for preview in query.
     */
    if (is_preview() && get_query_var('p') && 'publish' === get_post_status(get_query_var('p'))) {
        if (!isset($_GET['preview_id']) || !isset($_GET['preview_nonce']) || !wp_verify_nonce($_GET['preview_nonce'], 'post_preview_' . (int) $_GET['preview_id'])) {
            $wp_query->is_preview = false;
        }
    }
    if (is_admin() || is_search() || is_preview() || is_trackback() || is_favicon() || $is_IIS && !iis7_supports_permalinks()) {
        return;
    }
    if (!$requested_url && isset($_SERVER['HTTP_HOST'])) {
        // Build the URL in the address bar.
        $requested_url = is_ssl() ? 'https://' : 'http://';
        $requested_url .= $_SERVER['HTTP_HOST'];
        $requested_url .= $_SERVER['REQUEST_URI'];
    }
    $original = parse_url($requested_url);
    if (false === $original) {
        return;
    }
    $redirect = $original;
    $redirect_url = false;
    $redirect_obj = false;
    // Notice fixing.
    if (!isset($redirect['path'])) {
        $redirect['path'] = '';
    }
    if (!isset($redirect['query'])) {
        $redirect['query'] = '';
    }
    /*
     * If the original URL ended with non-breaking spaces, they were almost
     * certainly inserted by accident. Let's remove them, so the reader doesn't
     * see a 404 error with no obvious cause.
     */
    $redirect['path'] = preg_replace('|(%C2%A0)+$|i', '', $redirect['path']);
    // It's not a preview, so remove it from URL.
    if (get_query_var('preview')) {
        $redirect['query'] = remove_query_arg('preview', $redirect['query']);
    }
    $post_id = get_query_var('p');
    if (is_feed() && $post_id) {
        $redirect_url = get_post_comments_feed_link($post_id, get_query_var('feed'));
        $redirect_obj = get_post($post_id);
        if ($redirect_url) {
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type', 'feed'), $redirect_url);
            $redirect['path'] = parse_url($redirect_url, PHP_URL_PATH);
        }
    }
    if (is_singular() && $wp_query->post_count < 1 && $post_id) {
        $vars = $wpdb->get_results($wpdb->prepare("SELECT post_type, post_parent FROM {$wpdb->posts} WHERE ID = %d", $post_id));
        if (!empty($vars[0])) {
            $vars = $vars[0];
            if ('revision' === $vars->post_type && $vars->post_parent > 0) {
                $post_id = $vars->post_parent;
            }
            $redirect_url = get_permalink($post_id);
            $redirect_obj = get_post($post_id);
            if ($redirect_url) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    }
    // These tests give us a WP-generated permalink.
    if (is_404()) {
        // Redirect ?page_id, ?p=, ?attachment_id= to their respective URLs.
        $post_id = max(get_query_var('p'), get_query_var('page_id'), get_query_var('attachment_id'));
        $redirect_post = $post_id ? get_post($post_id) : false;
        if ($redirect_post) {
            $post_type_obj = get_post_type_object($redirect_post->post_type);
            if ($post_type_obj && $post_type_obj->public && 'auto-draft' !== $redirect_post->post_status) {
                $redirect_url = get_permalink($redirect_post);
                $redirect_obj = get_post($redirect_post);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
        $year = get_query_var('year');
        $month = get_query_var('monthnum');
        $day = get_query_var('day');
        if ($year && $month && $day) {
            $date = sprintf('%04d-%02d-%02d', $year, $month, $day);
            if (!wp_checkdate($month, $day, $year, $date)) {
                $redirect_url = get_month_link($year, $month);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum', 'day'), $redirect_url);
            }
        } elseif ($year && $month && $month > 12) {
            $redirect_url = get_year_link($year);
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum'), $redirect_url);
        }
        // Strip off non-existing <!--nextpage--> links from single posts or pages.
        if (get_query_var('page')) {
            $post_id = 0;
            if ($wp_query->queried_object instanceof WP_Post) {
                $post_id = $wp_query->queried_object->ID;
            } elseif ($wp_query->post) {
                $post_id = $wp_query->post->ID;
            }
            if ($post_id) {
                $redirect_url = get_permalink($post_id);
                $redirect_obj = get_post($post_id);
                $redirect['path'] = rtrim($redirect['path'], (int) get_query_var('page') . '/');
                $redirect['query'] = remove_query_arg('page', $redirect['query']);
            }
        }
        if (!$redirect_url) {
            $redirect_url = redirect_guess_404_permalink();
            if ($redirect_url) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('page', 'feed', 'p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    } elseif (is_object($wp_rewrite) && $wp_rewrite->using_permalinks()) {
        // Rewriting of old ?p=X, ?m=2004, ?m=200401, ?m=20040101.
        if (is_attachment() && !array_diff(array_keys($wp->query_vars), array('attachment', 'attachment_id')) && !$redirect_url) {
            if (!empty($_GET['attachment_id'])) {
                $redirect_url = get_attachment_link(get_query_var('attachment_id'));
                $redirect_obj = get_post(get_query_var('attachment_id'));
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('attachment_id', $redirect['query']);
                }
            } else {
                $redirect_url = get_attachment_link();
                $redirect_obj = get_post();
            }
        } elseif (is_single() && !empty($_GET['p']) && !$redirect_url) {
            $redirect_url = get_permalink(get_query_var('p'));
            $redirect_obj = get_post(get_query_var('p'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg(array('p', 'post_type'), $redirect['query']);
            }
        } elseif (is_single() && !empty($_GET['name']) && !$redirect_url) {
            $redirect_url = get_permalink($wp_query->get_queried_object_id());
            $redirect_obj = get_post($wp_query->get_queried_object_id());
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('name', $redirect['query']);
            }
        } elseif (is_page() && !empty($_GET['page_id']) && !$redirect_url) {
            $redirect_url = get_permalink(get_query_var('page_id'));
            $redirect_obj = get_post(get_query_var('page_id'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (is_page() && !is_feed() && !$redirect_url && 'page' === get_option('show_on_front') && get_queried_object_id() === (int) get_option('page_on_front')) {
            $redirect_url = home_url('/');
        } elseif (is_home() && !empty($_GET['page_id']) && !$redirect_url && 'page' === get_option('show_on_front') && get_query_var('page_id') === (int) get_option('page_for_posts')) {
            $redirect_url = get_permalink(get_option('page_for_posts'));
            $redirect_obj = get_post(get_option('page_for_posts'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (!empty($_GET['m']) && (is_year() || is_month() || is_day())) {
            $m = get_query_var('m');
            switch (strlen($m)) {
                case 4:
                    // Yearly.
                    $redirect_url = get_year_link($m);
                    break;
                case 6:
                    // Monthly.
                    $redirect_url = get_month_link(substr($m, 0, 4), substr($m, 4, 2));
                    break;
                case 8:
                    // Daily.
                    $redirect_url = get_day_link(substr($m, 0, 4), substr($m, 4, 2), substr($m, 6, 2));
                    break;
            }
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('m', $redirect['query']);
            }
            // Now moving on to non ?m=X year/month/day links.
        } elseif (is_date()) {
            $year = get_query_var('year');
            $month = get_query_var('monthnum');
            $day = get_query_var('day');
            if (is_day() && $year && $month && !empty($_GET['day'])) {
                $redirect_url = get_day_link($year, $month, $day);
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg(array('year', 'monthnum', 'day'), $redirect['query']);
                }
            } elseif (is_month() && $year && !empty($_GET['monthnum'])) {
                $redirect_url = get_month_link($year, $month);
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg(array('year', 'monthnum'), $redirect['query']);
                }
            } elseif (is_year() && !empty($_GET['year'])) {
                $redirect_url = get_year_link($year);
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('year', $redirect['query']);
                }
            }
        } elseif (is_author() && !empty($_GET['author']) && preg_match('|^[0-9]+$|', $_GET['author'])) {
            $author = get_userdata(get_query_var('author'));
            if (false !== $author && $wpdb->get_var($wpdb->prepare("SELECT ID FROM {$wpdb->posts} WHERE {$wpdb->posts}.post_author = %d AND {$wpdb->posts}.post_status = 'publish' LIMIT 1", $author->ID))) {
                $redirect_url = get_author_posts_url($author->ID, $author->user_nicename);
                $redirect_obj = $author;
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('author', $redirect['query']);
                }
            }
        } elseif (is_category() || is_tag() || is_tax()) {
            // Terms (tags/categories).
            $term_count = 0;
            foreach ($wp_query->tax_query->queried_terms as $tax_query) {
                if (isset($tax_query['terms']) && is_countable($tax_query['terms'])) {
                    $term_count += count($tax_query['terms']);
                }
            }
            $obj = $wp_query->get_queried_object();
            if ($term_count <= 1 && !empty($obj->term_id)) {
                $tax_url = get_term_link((int) $obj->term_id, $obj->taxonomy);
                if ($tax_url && !is_wp_error($tax_url)) {
                    if (!empty($redirect['query'])) {
                        // Strip taxonomy query vars off the URL.
                        $qv_remove = array('term', 'taxonomy');
                        if (is_category()) {
                            $qv_remove[] = 'category_name';
                            $qv_remove[] = 'cat';
                        } elseif (is_tag()) {
                            $qv_remove[] = 'tag';
                            $qv_remove[] = 'tag_id';
                        } else {
                            // Custom taxonomies will have a custom query var, remove those too.
                            $tax_obj = get_taxonomy($obj->taxonomy);
                            if (false !== $tax_obj->query_var) {
                                $qv_remove[] = $tax_obj->query_var;
                            }
                        }
                        $rewrite_vars = array_diff(array_keys($wp_query->query), array_keys($_GET));
                        // Check to see if all the query vars are coming from the rewrite, none are set via $_GET.
                        if (!array_diff($rewrite_vars, array_keys($_GET))) {
                            // Remove all of the per-tax query vars.
                            $redirect['query'] = remove_query_arg($qv_remove, $redirect['query']);
                            // Create the destination URL for this taxonomy.
                            $tax_url = parse_url($tax_url);
                            if (!empty($tax_url['query'])) {
                                // Taxonomy accessible via ?taxonomy=...&term=... or any custom query var.
                                parse_str($tax_url['query'], $query_vars);
                                $redirect['query'] = add_query_arg($query_vars, $redirect['query']);
                            } else {
                                // Taxonomy is accessible via a "pretty URL".
                                $redirect['path'] = $tax_url['path'];
                            }
                        } else {
                            // Some query vars are set via $_GET. Unset those from $_GET that exist via the rewrite.
                            foreach ($qv_remove as $_qv) {
                                if (isset($rewrite_vars[$_qv])) {
                                    $redirect['query'] = remove_query_arg($_qv, $redirect['query']);
                                }
                            }
                        }
                    }
                }
            }
        } elseif (is_single() && str_contains($wp_rewrite->permalink_structure, '%category%')) {
            $category_name = get_query_var('category_name');
            if ($category_name) {
                $category = get_category_by_path($category_name);
                if (!$category || is_wp_error($category) || !has_term($category->term_id, 'category', $wp_query->get_queried_object_id())) {
                    $redirect_url = get_permalink($wp_query->get_queried_object_id());
                    $redirect_obj = get_post($wp_query->get_queried_object_id());
                }
            }
        }
        // Post paging.
        if (is_singular() && get_query_var('page')) {
            $page = get_query_var('page');
            if (!$redirect_url) {
                $redirect_url = get_permalink(get_queried_object_id());
                $redirect_obj = get_post(get_queried_object_id());
            }
            if ($page > 1) {
                $redirect_url = trailingslashit($redirect_url);
                if (is_front_page()) {
                    $redirect_url .= user_trailingslashit("{$wp_rewrite->pagination_base}/{$page}", 'paged');
                } else {
                    $redirect_url .= user_trailingslashit($page, 'single_paged');
                }
            }
            $redirect['query'] = remove_query_arg('page', $redirect['query']);
        }
        if (get_query_var('sitemap')) {
            $redirect_url = get_sitemap_url(get_query_var('sitemap'), get_query_var('sitemap-subtype'), get_query_var('paged'));
            $redirect['query'] = remove_query_arg(array('sitemap', 'sitemap-subtype', 'paged'), $redirect['query']);
        } elseif (get_query_var('paged') || is_feed() || get_query_var('cpage')) {
            // Paging and feeds.
            $paged = get_query_var('paged');
            $feed = get_query_var('feed');
            $cpage = get_query_var('cpage');
            while (preg_match("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", $redirect['path']) || preg_match('#/(comments/?)?(feed|rss2?|rdf|atom)(/+)?$#', $redirect['path']) || preg_match("#/{$wp_rewrite->comments_pagination_base}-[0-9]+(/+)?\$#", $redirect['path'])) {
                // Strip off any existing paging.
                $redirect['path'] = preg_replace("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", '/', $redirect['path']);
                // Strip off feed endings.
                $redirect['path'] = preg_replace('#/(comments/?)?(feed|rss2?|rdf|atom)(/+|$)#', '/', $redirect['path']);
                // Strip off any existing comment paging.
                $redirect['path'] = preg_replace("#/{$wp_rewrite->comments_pagination_base}-[0-9]+?(/+)?\$#", '/', $redirect['path']);
            }
            $addl_path = '';
            $default_feed = get_default_feed();
            if (is_feed() && in_array($feed, $wp_rewrite->feeds, true)) {
                $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                if (!is_singular() && get_query_var('withcomments')) {
                    $addl_path .= 'comments/';
                }
                if ('rss' === $default_feed && 'feed' === $feed || 'rss' === $feed) {
                    $format = ('rss2' === $default_feed) ? '' : 'rss2';
                } else {
                    $format = ($default_feed === $feed || 'feed' === $feed) ? '' : $feed;
                }
                $addl_path .= user_trailingslashit('feed/' . $format, 'feed');
                $redirect['query'] = remove_query_arg('feed', $redirect['query']);
            } elseif (is_feed() && 'old' === $feed) {
                $old_feed_files = array('wp-atom.php' => 'atom', 'wp-commentsrss2.php' => 'comments_rss2', 'wp-feed.php' => $default_feed, 'wp-rdf.php' => 'rdf', 'wp-rss.php' => 'rss2', 'wp-rss2.php' => 'rss2');
                if (isset($old_feed_files[basename($redirect['path'])])) {
                    $redirect_url = get_feed_link($old_feed_files[basename($redirect['path'])]);
                    wp_redirect($redirect_url, 301);
                    die;
                }
            }
            if ($paged > 0) {
                $redirect['query'] = remove_query_arg('paged', $redirect['query']);
                if (!is_feed()) {
                    if (!is_single()) {
                        $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                        if ($paged > 1) {
                            $addl_path .= user_trailingslashit("{$wp_rewrite->pagination_base}/{$paged}", 'paged');
                        }
                    }
                } elseif ($paged > 1) {
                    $redirect['query'] = add_query_arg('paged', $paged, $redirect['query']);
                }
            }
            $default_comments_page = get_option('default_comments_page');
            if (get_option('page_comments') && ('newest' === $default_comments_page && $cpage > 0 || 'newest' !== $default_comments_page && $cpage > 1)) {
                $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                $addl_path .= user_trailingslashit($wp_rewrite->comments_pagination_base . '-' . $cpage, 'commentpaged');
                $redirect['query'] = remove_query_arg('cpage', $redirect['query']);
            }
            // Strip off trailing /index.php/.
            $redirect['path'] = preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/?$|', '/', $redirect['path']);
            $redirect['path'] = user_trailingslashit($redirect['path']);
            if (!empty($addl_path) && $wp_rewrite->using_index_permalinks() && !str_contains($redirect['path'], '/' . $wp_rewrite->index . '/')) {
                $redirect['path'] = trailingslashit($redirect['path']) . $wp_rewrite->index . '/';
            }
            if (!empty($addl_path)) {
                $redirect['path'] = trailingslashit($redirect['path']) . $addl_path;
            }
            $redirect_url = $redirect['scheme'] . '://' . $redirect['host'] . $redirect['path'];
        }
        if ('wp-register.php' === basename($redirect['path'])) {
            if (is_multisite()) {
                /** This filter is documented in wp-login.php */
                $redirect_url = apply_filters('wp_signup_location', network_site_url('wp-signup.php'));
            } else {
                $redirect_url = wp_registration_url();
            }
            wp_redirect($redirect_url, 301);
            die;
        }
    }
    $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    // Tack on any additional query vars.
    if ($redirect_url && !empty($redirect['query'])) {
        parse_str($redirect['query'], $_parsed_query);
        $redirect = parse_url($redirect_url);
        if (!empty($_parsed_query['name']) && !empty($redirect['query'])) {
            parse_str($redirect['query'], $_parsed_redirect_query);
            if (empty($_parsed_redirect_query['name'])) {
                unset($_parsed_query['name']);
            }
        }
        $_parsed_query = array_combine(rawurlencode_deep(array_keys($_parsed_query)), rawurlencode_deep(array_values($_parsed_query)));
        $redirect_url = add_query_arg($_parsed_query, $redirect_url);
    }
    if ($redirect_url) {
        $redirect = parse_url($redirect_url);
    }
    // www.example.com vs. example.com
    $user_home = parse_url(home_url());
    if (!empty($user_home['host'])) {
        $redirect['host'] = $user_home['host'];
    }
    if (empty($user_home['path'])) {
        $user_home['path'] = '/';
    }
    // Handle ports.
    if (!empty($user_home['port'])) {
        $redirect['port'] = $user_home['port'];
    } else {
        unset($redirect['port']);
    }
    // Trailing /index.php.
    $redirect['path'] = preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/*?$|', '/', $redirect['path']);
    $punctuation_pattern = implode('|', array_map('preg_quote', array(
        ' ',
        '%20',
        // Space.
        '!',
        '%21',
        // Exclamation mark.
        '"',
        '%22',
        // Double quote.
        "'",
        '%27',
        // Single quote.
        '(',
        '%28',
        // Opening bracket.
        ')',
        '%29',
        // Closing bracket.
        ',',
        '%2C',
        // Comma.
        '.',
        '%2E',
        // Period.
        ';',
        '%3B',
        // Semicolon.
        '{',
        '%7B',
        // Opening curly bracket.
        '}',
        '%7D',
        // Closing curly bracket.
        '%E2%80%9C',
        // Opening curly quote.
        '%E2%80%9D',
    )));
    // Remove trailing spaces and end punctuation from the path.
    $redirect['path'] = preg_replace("#({$punctuation_pattern})+\$#", '', $redirect['path']);
    if (!empty($redirect['query'])) {
        // Remove trailing spaces and end punctuation from certain terminating query string args.
        $redirect['query'] = preg_replace("#((^|&)(p|page_id|cat|tag)=[^&]*?)({$punctuation_pattern})+\$#", '$1', $redirect['query']);
        // Clean up empty query strings.
        $redirect['query'] = trim(preg_replace('#(^|&)(p|page_id|cat|tag)=?(&|$)#', '&', $redirect['query']), '&');
        // Redirect obsolete feeds.
        $redirect['query'] = preg_replace('#(^|&)feed=rss(&|$)#', '$1feed=rss2$2', $redirect['query']);
        // Remove redundant leading ampersands.
        $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    }
    // Strip /index.php/ when we're not using PATHINFO permalinks.
    if (!$wp_rewrite->using_index_permalinks()) {
        $redirect['path'] = str_replace('/' . $wp_rewrite->index . '/', '/', $redirect['path']);
    }
    // Trailing slashes.
    if (is_object($wp_rewrite) && $wp_rewrite->using_permalinks() && !is_404() && (!is_front_page() || is_front_page() && get_query_var('paged') > 1)) {
        $user_ts_type = '';
        if (get_query_var('paged') > 0) {
            $user_ts_type = 'paged';
        } else {
            foreach (array('single', 'category', 'page', 'day', 'month', 'year', 'home') as $type) {
                $func = 'is_' . $type;
                if (call_user_func($func)) {
                    $user_ts_type = $type;
                    break;
                }
            }
        }
        $redirect['path'] = user_trailingslashit($redirect['path'], $user_ts_type);
    } elseif (is_front_page()) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Remove trailing slash for robots.txt or sitemap requests.
    if (is_robots() || !empty(get_query_var('sitemap')) || !empty(get_query_var('sitemap-stylesheet'))) {
        $redirect['path'] = untrailingslashit($redirect['path']);
    }
    // Strip multiple slashes out of the URL.
    if (str_contains($redirect['path'], '//')) {
        $redirect['path'] = preg_replace('|/+|', '/', $redirect['path']);
    }
    // Always trailing slash the Front Page URL.
    if (trailingslashit($redirect['path']) === trailingslashit($user_home['path'])) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    $original_host_low = strtolower($original['host']);
    $redirect_host_low = strtolower($redirect['host']);
    /*
     * Ignore differences in host capitalization, as this can lead to infinite redirects.
     * Only redirect no-www <=> yes-www.
     */
    if ($original_host_low === $redirect_host_low || 'www.' . $original_host_low !== $redirect_host_low && 'www.' . $redirect_host_low !== $original_host_low) {
        $redirect['host'] = $original['host'];
    }
    $compare_original = array($original['host'], $original['path']);
    if (!empty($original['port'])) {
        $compare_original[] = $original['port'];
    }
    if (!empty($original['query'])) {
        $compare_original[] = $original['query'];
    }
    $compare_redirect = array($redirect['host'], $redirect['path']);
    if (!empty($redirect['port'])) {
        $compare_redirect[] = $redirect['port'];
    }
    if (!empty($redirect['query'])) {
        $compare_redirect[] = $redirect['query'];
    }
    if ($compare_original !== $compare_redirect) {
        $redirect_url = $redirect['scheme'] . '://' . $redirect['host'];
        if (!empty($redirect['port'])) {
            $redirect_url .= ':' . $redirect['port'];
        }
        $redirect_url .= $redirect['path'];
        if (!empty($redirect['query'])) {
            $redirect_url .= '?' . $redirect['query'];
        }
    }
    if (!$redirect_url || $redirect_url === $requested_url) {
        return;
    }
    // Hex-encoded octets are case-insensitive.
    if (str_contains($requested_url, '%')) {
        if (!function_exists('lowercase_octets')) {
            /**
             * Converts the first hex-encoded octet match to lowercase.
             *
             * @since 3.1.0
             * @ignore
             *
             * @param array $matches Hex-encoded octet matches for the requested URL.
             * @return string Lowercased version of the first match.
             */
            function lowercase_octets($matches)
            {
                return strtolower($matches[0]);
            }
        }
        $requested_url = preg_replace_callback('|%[a-fA-F0-9][a-fA-F0-9]|', 'lowercase_octets', $requested_url);
    }
    if ($redirect_obj instanceof WP_Post) {
        $post_status_obj = get_post_status_object(get_post_status($redirect_obj));
        /*
         * Unset the redirect object and URL if they are not readable by the user.
         * This condition is a little confusing as the condition needs to pass if
         * the post is not readable by the user. That's why there are ! (not) conditions
         * throughout.
         */
        if (!($post_status_obj->private && current_user_can('read_post', $redirect_obj->ID)) && !is_post_publicly_viewable($redirect_obj)) {
            $redirect_obj = false;
            $redirect_url = false;
        }
    }
    /**
     * Filters the canonical redirect URL.
     *
     * Returning false to this filter will cancel the redirect.
     *
     * @since 2.3.0
     *
     * @param string $redirect_url  The redirect URL.
     * @param string $requested_url The requested URL.
     */
    $redirect_url = apply_filters('redirect_canonical', $redirect_url, $requested_url);
    // Yes, again -- in case the filter aborted the request.
    if (!$redirect_url || strip_fragment_from_url($redirect_url) === strip_fragment_from_url($requested_url)) {
        return;
    }
    if ($do_redirect) {
        // Protect against chained redirects.
        if (!redirect_canonical($redirect_url, false)) {
            wp_redirect($redirect_url, 301);
            exit;
        } else {
            // Debug.
            // die("1: $redirect_url<br />2: " . redirect_canonical( $redirect_url, false ) );
            return;
        }
    } else {
        return $redirect_url;
    }
}

WordPress Version: 6.2

/**
 * Canonical API to handle WordPress Redirecting
 *
 * Based on "Permalink Redirect" from Scott Yang and "Enforce www. Preference"
 * by Mark Jaquith
 *
 * @package WordPress
 * @since 2.3.0
 */
/**
 * Redirects incoming links to the proper URL based on the site url.
 *
 * Search engines consider www.somedomain.com and somedomain.com to be two
 * different URLs when they both go to the same location. This SEO enhancement
 * prevents penalty for duplicate content by redirecting all incoming links to
 * one or the other.
 *
 * Prevents redirection for feeds, trackbacks, searches, and
 * admin URLs. Does not redirect on non-pretty-permalink-supporting IIS 7+,
 * page/post previews, WP admin, Trackbacks, robots.txt, favicon.ico, searches,
 * or on POST requests.
 *
 * Will also attempt to find the correct link when a user enters a URL that does
 * not exist based on exact WordPress query. Will instead try to parse the URL
 * or query in an attempt to figure the correct page to go to.
 *
 * @since 2.3.0
 *
 * @global WP_Rewrite $wp_rewrite WordPress rewrite component.
 * @global bool       $is_IIS
 * @global WP_Query   $wp_query   WordPress Query object.
 * @global wpdb       $wpdb       WordPress database abstraction object.
 * @global WP         $wp         Current WordPress environment instance.
 *
 * @param string $requested_url Optional. The URL that was requested, used to
 *                              figure if redirect is needed.
 * @param bool   $do_redirect   Optional. Redirect to the new URL.
 * @return string|void The string of the URL, if redirect needed.
 */
function redirect_canonical($requested_url = null, $do_redirect = true)
{
    global $wp_rewrite, $is_IIS, $wp_query, $wpdb, $wp;
    if (isset($_SERVER['REQUEST_METHOD']) && !in_array(strtoupper($_SERVER['REQUEST_METHOD']), array('GET', 'HEAD'), true)) {
        return;
    }
    // If we're not in wp-admin and the post has been published and preview nonce
    // is non-existent or invalid then no need for preview in query.
    if (is_preview() && get_query_var('p') && 'publish' === get_post_status(get_query_var('p'))) {
        if (!isset($_GET['preview_id']) || !isset($_GET['preview_nonce']) || !wp_verify_nonce($_GET['preview_nonce'], 'post_preview_' . (int) $_GET['preview_id'])) {
            $wp_query->is_preview = false;
        }
    }
    if (is_admin() || is_search() || is_preview() || is_trackback() || is_favicon() || $is_IIS && !iis7_supports_permalinks()) {
        return;
    }
    if (!$requested_url && isset($_SERVER['HTTP_HOST'])) {
        // Build the URL in the address bar.
        $requested_url = is_ssl() ? 'https://' : 'http://';
        $requested_url .= $_SERVER['HTTP_HOST'];
        $requested_url .= $_SERVER['REQUEST_URI'];
    }
    $original = parse_url($requested_url);
    if (false === $original) {
        return;
    }
    $redirect = $original;
    $redirect_url = false;
    $redirect_obj = false;
    // Notice fixing.
    if (!isset($redirect['path'])) {
        $redirect['path'] = '';
    }
    if (!isset($redirect['query'])) {
        $redirect['query'] = '';
    }
    /*
     * If the original URL ended with non-breaking spaces, they were almost
     * certainly inserted by accident. Let's remove them, so the reader doesn't
     * see a 404 error with no obvious cause.
     */
    $redirect['path'] = preg_replace('|(%C2%A0)+$|i', '', $redirect['path']);
    // It's not a preview, so remove it from URL.
    if (get_query_var('preview')) {
        $redirect['query'] = remove_query_arg('preview', $redirect['query']);
    }
    $post_id = get_query_var('p');
    if (is_feed() && $post_id) {
        $redirect_url = get_post_comments_feed_link($post_id, get_query_var('feed'));
        $redirect_obj = get_post($post_id);
        if ($redirect_url) {
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type', 'feed'), $redirect_url);
            $redirect['path'] = parse_url($redirect_url, PHP_URL_PATH);
        }
    }
    if (is_singular() && $wp_query->post_count < 1 && $post_id) {
        $vars = $wpdb->get_results($wpdb->prepare("SELECT post_type, post_parent FROM {$wpdb->posts} WHERE ID = %d", $post_id));
        if (!empty($vars[0])) {
            $vars = $vars[0];
            if ('revision' === $vars->post_type && $vars->post_parent > 0) {
                $post_id = $vars->post_parent;
            }
            $redirect_url = get_permalink($post_id);
            $redirect_obj = get_post($post_id);
            if ($redirect_url) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    }
    // These tests give us a WP-generated permalink.
    if (is_404()) {
        // Redirect ?page_id, ?p=, ?attachment_id= to their respective URLs.
        $post_id = max(get_query_var('p'), get_query_var('page_id'), get_query_var('attachment_id'));
        $redirect_post = $post_id ? get_post($post_id) : false;
        if ($redirect_post) {
            $post_type_obj = get_post_type_object($redirect_post->post_type);
            if ($post_type_obj && $post_type_obj->public && 'auto-draft' !== $redirect_post->post_status) {
                $redirect_url = get_permalink($redirect_post);
                $redirect_obj = get_post($redirect_post);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
        $year = get_query_var('year');
        $month = get_query_var('monthnum');
        $day = get_query_var('day');
        if ($year && $month && $day) {
            $date = sprintf('%04d-%02d-%02d', $year, $month, $day);
            if (!wp_checkdate($month, $day, $year, $date)) {
                $redirect_url = get_month_link($year, $month);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum', 'day'), $redirect_url);
            }
        } elseif ($year && $month && $month > 12) {
            $redirect_url = get_year_link($year);
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum'), $redirect_url);
        }
        // Strip off non-existing <!--nextpage--> links from single posts or pages.
        if (get_query_var('page')) {
            $post_id = 0;
            if ($wp_query->queried_object instanceof WP_Post) {
                $post_id = $wp_query->queried_object->ID;
            } elseif ($wp_query->post) {
                $post_id = $wp_query->post->ID;
            }
            if ($post_id) {
                $redirect_url = get_permalink($post_id);
                $redirect_obj = get_post($post_id);
                $redirect['path'] = rtrim($redirect['path'], (int) get_query_var('page') . '/');
                $redirect['query'] = remove_query_arg('page', $redirect['query']);
            }
        }
        if (!$redirect_url) {
            $redirect_url = redirect_guess_404_permalink();
            if ($redirect_url) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('page', 'feed', 'p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    } elseif (is_object($wp_rewrite) && $wp_rewrite->using_permalinks()) {
        // Rewriting of old ?p=X, ?m=2004, ?m=200401, ?m=20040101.
        if (is_attachment() && !array_diff(array_keys($wp->query_vars), array('attachment', 'attachment_id')) && !$redirect_url) {
            if (!empty($_GET['attachment_id'])) {
                $redirect_url = get_attachment_link(get_query_var('attachment_id'));
                $redirect_obj = get_post(get_query_var('attachment_id'));
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('attachment_id', $redirect['query']);
                }
            } else {
                $redirect_url = get_attachment_link();
                $redirect_obj = get_post();
            }
        } elseif (is_single() && !empty($_GET['p']) && !$redirect_url) {
            $redirect_url = get_permalink(get_query_var('p'));
            $redirect_obj = get_post(get_query_var('p'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg(array('p', 'post_type'), $redirect['query']);
            }
        } elseif (is_single() && !empty($_GET['name']) && !$redirect_url) {
            $redirect_url = get_permalink($wp_query->get_queried_object_id());
            $redirect_obj = get_post($wp_query->get_queried_object_id());
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('name', $redirect['query']);
            }
        } elseif (is_page() && !empty($_GET['page_id']) && !$redirect_url) {
            $redirect_url = get_permalink(get_query_var('page_id'));
            $redirect_obj = get_post(get_query_var('page_id'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (is_page() && !is_feed() && !$redirect_url && 'page' === get_option('show_on_front') && get_queried_object_id() === (int) get_option('page_on_front')) {
            $redirect_url = home_url('/');
        } elseif (is_home() && !empty($_GET['page_id']) && !$redirect_url && 'page' === get_option('show_on_front') && get_query_var('page_id') === (int) get_option('page_for_posts')) {
            $redirect_url = get_permalink(get_option('page_for_posts'));
            $redirect_obj = get_post(get_option('page_for_posts'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (!empty($_GET['m']) && (is_year() || is_month() || is_day())) {
            $m = get_query_var('m');
            switch (strlen($m)) {
                case 4:
                    // Yearly.
                    $redirect_url = get_year_link($m);
                    break;
                case 6:
                    // Monthly.
                    $redirect_url = get_month_link(substr($m, 0, 4), substr($m, 4, 2));
                    break;
                case 8:
                    // Daily.
                    $redirect_url = get_day_link(substr($m, 0, 4), substr($m, 4, 2), substr($m, 6, 2));
                    break;
            }
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('m', $redirect['query']);
            }
            // Now moving on to non ?m=X year/month/day links.
        } elseif (is_date()) {
            $year = get_query_var('year');
            $month = get_query_var('monthnum');
            $day = get_query_var('day');
            if (is_day() && $year && $month && !empty($_GET['day'])) {
                $redirect_url = get_day_link($year, $month, $day);
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg(array('year', 'monthnum', 'day'), $redirect['query']);
                }
            } elseif (is_month() && $year && !empty($_GET['monthnum'])) {
                $redirect_url = get_month_link($year, $month);
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg(array('year', 'monthnum'), $redirect['query']);
                }
            } elseif (is_year() && !empty($_GET['year'])) {
                $redirect_url = get_year_link($year);
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('year', $redirect['query']);
                }
            }
        } elseif (is_author() && !empty($_GET['author']) && preg_match('|^[0-9]+$|', $_GET['author'])) {
            $author = get_userdata(get_query_var('author'));
            if (false !== $author && $wpdb->get_var($wpdb->prepare("SELECT ID FROM {$wpdb->posts} WHERE {$wpdb->posts}.post_author = %d AND {$wpdb->posts}.post_status = 'publish' LIMIT 1", $author->ID))) {
                $redirect_url = get_author_posts_url($author->ID, $author->user_nicename);
                $redirect_obj = $author;
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('author', $redirect['query']);
                }
            }
        } elseif (is_category() || is_tag() || is_tax()) {
            // Terms (tags/categories).
            $term_count = 0;
            foreach ($wp_query->tax_query->queried_terms as $tax_query) {
                if (isset($tax_query['terms']) && is_countable($tax_query['terms'])) {
                    $term_count += count($tax_query['terms']);
                }
            }
            $obj = $wp_query->get_queried_object();
            if ($term_count <= 1 && !empty($obj->term_id)) {
                $tax_url = get_term_link((int) $obj->term_id, $obj->taxonomy);
                if ($tax_url && !is_wp_error($tax_url)) {
                    if (!empty($redirect['query'])) {
                        // Strip taxonomy query vars off the URL.
                        $qv_remove = array('term', 'taxonomy');
                        if (is_category()) {
                            $qv_remove[] = 'category_name';
                            $qv_remove[] = 'cat';
                        } elseif (is_tag()) {
                            $qv_remove[] = 'tag';
                            $qv_remove[] = 'tag_id';
                        } else {
                            // Custom taxonomies will have a custom query var, remove those too.
                            $tax_obj = get_taxonomy($obj->taxonomy);
                            if (false !== $tax_obj->query_var) {
                                $qv_remove[] = $tax_obj->query_var;
                            }
                        }
                        $rewrite_vars = array_diff(array_keys($wp_query->query), array_keys($_GET));
                        // Check to see if all the query vars are coming from the rewrite, none are set via $_GET.
                        if (!array_diff($rewrite_vars, array_keys($_GET))) {
                            // Remove all of the per-tax query vars.
                            $redirect['query'] = remove_query_arg($qv_remove, $redirect['query']);
                            // Create the destination URL for this taxonomy.
                            $tax_url = parse_url($tax_url);
                            if (!empty($tax_url['query'])) {
                                // Taxonomy accessible via ?taxonomy=...&term=... or any custom query var.
                                parse_str($tax_url['query'], $query_vars);
                                $redirect['query'] = add_query_arg($query_vars, $redirect['query']);
                            } else {
                                // Taxonomy is accessible via a "pretty URL".
                                $redirect['path'] = $tax_url['path'];
                            }
                        } else {
                            // Some query vars are set via $_GET. Unset those from $_GET that exist via the rewrite.
                            foreach ($qv_remove as $_qv) {
                                if (isset($rewrite_vars[$_qv])) {
                                    $redirect['query'] = remove_query_arg($_qv, $redirect['query']);
                                }
                            }
                        }
                    }
                }
            }
        } elseif (is_single() && strpos($wp_rewrite->permalink_structure, '%category%') !== false) {
            $category_name = get_query_var('category_name');
            if ($category_name) {
                $category = get_category_by_path($category_name);
                if (!$category || is_wp_error($category) || !has_term($category->term_id, 'category', $wp_query->get_queried_object_id())) {
                    $redirect_url = get_permalink($wp_query->get_queried_object_id());
                    $redirect_obj = get_post($wp_query->get_queried_object_id());
                }
            }
        }
        // Post paging.
        if (is_singular() && get_query_var('page')) {
            $page = get_query_var('page');
            if (!$redirect_url) {
                $redirect_url = get_permalink(get_queried_object_id());
                $redirect_obj = get_post(get_queried_object_id());
            }
            if ($page > 1) {
                $redirect_url = trailingslashit($redirect_url);
                if (is_front_page()) {
                    $redirect_url .= user_trailingslashit("{$wp_rewrite->pagination_base}/{$page}", 'paged');
                } else {
                    $redirect_url .= user_trailingslashit($page, 'single_paged');
                }
            }
            $redirect['query'] = remove_query_arg('page', $redirect['query']);
        }
        if (get_query_var('sitemap')) {
            $redirect_url = get_sitemap_url(get_query_var('sitemap'), get_query_var('sitemap-subtype'), get_query_var('paged'));
            $redirect['query'] = remove_query_arg(array('sitemap', 'sitemap-subtype', 'paged'), $redirect['query']);
        } elseif (get_query_var('paged') || is_feed() || get_query_var('cpage')) {
            // Paging and feeds.
            $paged = get_query_var('paged');
            $feed = get_query_var('feed');
            $cpage = get_query_var('cpage');
            while (preg_match("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", $redirect['path']) || preg_match('#/(comments/?)?(feed|rss2?|rdf|atom)(/+)?$#', $redirect['path']) || preg_match("#/{$wp_rewrite->comments_pagination_base}-[0-9]+(/+)?\$#", $redirect['path'])) {
                // Strip off any existing paging.
                $redirect['path'] = preg_replace("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", '/', $redirect['path']);
                // Strip off feed endings.
                $redirect['path'] = preg_replace('#/(comments/?)?(feed|rss2?|rdf|atom)(/+|$)#', '/', $redirect['path']);
                // Strip off any existing comment paging.
                $redirect['path'] = preg_replace("#/{$wp_rewrite->comments_pagination_base}-[0-9]+?(/+)?\$#", '/', $redirect['path']);
            }
            $addl_path = '';
            $default_feed = get_default_feed();
            if (is_feed() && in_array($feed, $wp_rewrite->feeds, true)) {
                $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                if (!is_singular() && get_query_var('withcomments')) {
                    $addl_path .= 'comments/';
                }
                if ('rss' === $default_feed && 'feed' === $feed || 'rss' === $feed) {
                    $format = ('rss2' === $default_feed) ? '' : 'rss2';
                } else {
                    $format = ($default_feed === $feed || 'feed' === $feed) ? '' : $feed;
                }
                $addl_path .= user_trailingslashit('feed/' . $format, 'feed');
                $redirect['query'] = remove_query_arg('feed', $redirect['query']);
            } elseif (is_feed() && 'old' === $feed) {
                $old_feed_files = array('wp-atom.php' => 'atom', 'wp-commentsrss2.php' => 'comments_rss2', 'wp-feed.php' => $default_feed, 'wp-rdf.php' => 'rdf', 'wp-rss.php' => 'rss2', 'wp-rss2.php' => 'rss2');
                if (isset($old_feed_files[basename($redirect['path'])])) {
                    $redirect_url = get_feed_link($old_feed_files[basename($redirect['path'])]);
                    wp_redirect($redirect_url, 301);
                    die;
                }
            }
            if ($paged > 0) {
                $redirect['query'] = remove_query_arg('paged', $redirect['query']);
                if (!is_feed()) {
                    if (!is_single()) {
                        $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                        if ($paged > 1) {
                            $addl_path .= user_trailingslashit("{$wp_rewrite->pagination_base}/{$paged}", 'paged');
                        }
                    }
                } elseif ($paged > 1) {
                    $redirect['query'] = add_query_arg('paged', $paged, $redirect['query']);
                }
            }
            $default_comments_page = get_option('default_comments_page');
            if (get_option('page_comments') && ('newest' === $default_comments_page && $cpage > 0 || 'newest' !== $default_comments_page && $cpage > 1)) {
                $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                $addl_path .= user_trailingslashit($wp_rewrite->comments_pagination_base . '-' . $cpage, 'commentpaged');
                $redirect['query'] = remove_query_arg('cpage', $redirect['query']);
            }
            // Strip off trailing /index.php/.
            $redirect['path'] = preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/?$|', '/', $redirect['path']);
            $redirect['path'] = user_trailingslashit($redirect['path']);
            if (!empty($addl_path) && $wp_rewrite->using_index_permalinks() && strpos($redirect['path'], '/' . $wp_rewrite->index . '/') === false) {
                $redirect['path'] = trailingslashit($redirect['path']) . $wp_rewrite->index . '/';
            }
            if (!empty($addl_path)) {
                $redirect['path'] = trailingslashit($redirect['path']) . $addl_path;
            }
            $redirect_url = $redirect['scheme'] . '://' . $redirect['host'] . $redirect['path'];
        }
        if ('wp-register.php' === basename($redirect['path'])) {
            if (is_multisite()) {
                /** This filter is documented in wp-login.php */
                $redirect_url = apply_filters('wp_signup_location', network_site_url('wp-signup.php'));
            } else {
                $redirect_url = wp_registration_url();
            }
            wp_redirect($redirect_url, 301);
            die;
        }
    }
    $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    // Tack on any additional query vars.
    if ($redirect_url && !empty($redirect['query'])) {
        parse_str($redirect['query'], $_parsed_query);
        $redirect = parse_url($redirect_url);
        if (!empty($_parsed_query['name']) && !empty($redirect['query'])) {
            parse_str($redirect['query'], $_parsed_redirect_query);
            if (empty($_parsed_redirect_query['name'])) {
                unset($_parsed_query['name']);
            }
        }
        $_parsed_query = array_combine(rawurlencode_deep(array_keys($_parsed_query)), rawurlencode_deep(array_values($_parsed_query)));
        $redirect_url = add_query_arg($_parsed_query, $redirect_url);
    }
    if ($redirect_url) {
        $redirect = parse_url($redirect_url);
    }
    // www.example.com vs. example.com
    $user_home = parse_url(home_url());
    if (!empty($user_home['host'])) {
        $redirect['host'] = $user_home['host'];
    }
    if (empty($user_home['path'])) {
        $user_home['path'] = '/';
    }
    // Handle ports.
    if (!empty($user_home['port'])) {
        $redirect['port'] = $user_home['port'];
    } else {
        unset($redirect['port']);
    }
    // Trailing /index.php.
    $redirect['path'] = preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/*?$|', '/', $redirect['path']);
    $punctuation_pattern = implode('|', array_map('preg_quote', array(
        ' ',
        '%20',
        // Space.
        '!',
        '%21',
        // Exclamation mark.
        '"',
        '%22',
        // Double quote.
        "'",
        '%27',
        // Single quote.
        '(',
        '%28',
        // Opening bracket.
        ')',
        '%29',
        // Closing bracket.
        ',',
        '%2C',
        // Comma.
        '.',
        '%2E',
        // Period.
        ';',
        '%3B',
        // Semicolon.
        '{',
        '%7B',
        // Opening curly bracket.
        '}',
        '%7D',
        // Closing curly bracket.
        '%E2%80%9C',
        // Opening curly quote.
        '%E2%80%9D',
    )));
    // Remove trailing spaces and end punctuation from the path.
    $redirect['path'] = preg_replace("#({$punctuation_pattern})+\$#", '', $redirect['path']);
    if (!empty($redirect['query'])) {
        // Remove trailing spaces and end punctuation from certain terminating query string args.
        $redirect['query'] = preg_replace("#((^|&)(p|page_id|cat|tag)=[^&]*?)({$punctuation_pattern})+\$#", '$1', $redirect['query']);
        // Clean up empty query strings.
        $redirect['query'] = trim(preg_replace('#(^|&)(p|page_id|cat|tag)=?(&|$)#', '&', $redirect['query']), '&');
        // Redirect obsolete feeds.
        $redirect['query'] = preg_replace('#(^|&)feed=rss(&|$)#', '$1feed=rss2$2', $redirect['query']);
        // Remove redundant leading ampersands.
        $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    }
    // Strip /index.php/ when we're not using PATHINFO permalinks.
    if (!$wp_rewrite->using_index_permalinks()) {
        $redirect['path'] = str_replace('/' . $wp_rewrite->index . '/', '/', $redirect['path']);
    }
    // Trailing slashes.
    if (is_object($wp_rewrite) && $wp_rewrite->using_permalinks() && !is_404() && (!is_front_page() || is_front_page() && get_query_var('paged') > 1)) {
        $user_ts_type = '';
        if (get_query_var('paged') > 0) {
            $user_ts_type = 'paged';
        } else {
            foreach (array('single', 'category', 'page', 'day', 'month', 'year', 'home') as $type) {
                $func = 'is_' . $type;
                if (call_user_func($func)) {
                    $user_ts_type = $type;
                    break;
                }
            }
        }
        $redirect['path'] = user_trailingslashit($redirect['path'], $user_ts_type);
    } elseif (is_front_page()) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Remove trailing slash for robots.txt or sitemap requests.
    if (is_robots() || !empty(get_query_var('sitemap')) || !empty(get_query_var('sitemap-stylesheet'))) {
        $redirect['path'] = untrailingslashit($redirect['path']);
    }
    // Strip multiple slashes out of the URL.
    if (strpos($redirect['path'], '//') > -1) {
        $redirect['path'] = preg_replace('|/+|', '/', $redirect['path']);
    }
    // Always trailing slash the Front Page URL.
    if (trailingslashit($redirect['path']) === trailingslashit($user_home['path'])) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    $original_host_low = strtolower($original['host']);
    $redirect_host_low = strtolower($redirect['host']);
    // Ignore differences in host capitalization, as this can lead to infinite redirects.
    // Only redirect no-www <=> yes-www.
    if ($original_host_low === $redirect_host_low || 'www.' . $original_host_low !== $redirect_host_low && 'www.' . $redirect_host_low !== $original_host_low) {
        $redirect['host'] = $original['host'];
    }
    $compare_original = array($original['host'], $original['path']);
    if (!empty($original['port'])) {
        $compare_original[] = $original['port'];
    }
    if (!empty($original['query'])) {
        $compare_original[] = $original['query'];
    }
    $compare_redirect = array($redirect['host'], $redirect['path']);
    if (!empty($redirect['port'])) {
        $compare_redirect[] = $redirect['port'];
    }
    if (!empty($redirect['query'])) {
        $compare_redirect[] = $redirect['query'];
    }
    if ($compare_original !== $compare_redirect) {
        $redirect_url = $redirect['scheme'] . '://' . $redirect['host'];
        if (!empty($redirect['port'])) {
            $redirect_url .= ':' . $redirect['port'];
        }
        $redirect_url .= $redirect['path'];
        if (!empty($redirect['query'])) {
            $redirect_url .= '?' . $redirect['query'];
        }
    }
    if (!$redirect_url || $redirect_url === $requested_url) {
        return;
    }
    // Hex-encoded octets are case-insensitive.
    if (false !== strpos($requested_url, '%')) {
        if (!function_exists('lowercase_octets')) {
            /**
             * Converts the first hex-encoded octet match to lowercase.
             *
             * @since 3.1.0
             * @ignore
             *
             * @param array $matches Hex-encoded octet matches for the requested URL.
             * @return string Lowercased version of the first match.
             */
            function lowercase_octets($matches)
            {
                return strtolower($matches[0]);
            }
        }
        $requested_url = preg_replace_callback('|%[a-fA-F0-9][a-fA-F0-9]|', 'lowercase_octets', $requested_url);
    }
    if ($redirect_obj instanceof WP_Post) {
        $post_status_obj = get_post_status_object(get_post_status($redirect_obj));
        /*
         * Unset the redirect object and URL if they are not readable by the user.
         * This condition is a little confusing as the condition needs to pass if
         * the post is not readable by the user. That's why there are ! (not) conditions
         * throughout.
         */
        if (!($post_status_obj->private && current_user_can('read_post', $redirect_obj->ID)) && !is_post_publicly_viewable($redirect_obj)) {
            $redirect_obj = false;
            $redirect_url = false;
        }
    }
    /**
     * Filters the canonical redirect URL.
     *
     * Returning false to this filter will cancel the redirect.
     *
     * @since 2.3.0
     *
     * @param string $redirect_url  The redirect URL.
     * @param string $requested_url The requested URL.
     */
    $redirect_url = apply_filters('redirect_canonical', $redirect_url, $requested_url);
    // Yes, again -- in case the filter aborted the request.
    if (!$redirect_url || strip_fragment_from_url($redirect_url) === strip_fragment_from_url($requested_url)) {
        return;
    }
    if ($do_redirect) {
        // Protect against chained redirects.
        if (!redirect_canonical($redirect_url, false)) {
            wp_redirect($redirect_url, 301);
            exit;
        } else {
            // Debug.
            // die("1: $redirect_url<br />2: " . redirect_canonical( $redirect_url, false ) );
            return;
        }
    } else {
        return $redirect_url;
    }
}

WordPress Version: 1.1

/**
 * Canonical API to handle WordPress Redirecting
 *
 * Based on "Permalink Redirect" from Scott Yang and "Enforce www. Preference"
 * by Mark Jaquith
 *
 * @package WordPress
 * @since 2.3.0
 */
/**
 * Redirects incoming links to the proper URL based on the site url.
 *
 * Search engines consider www.somedomain.com and somedomain.com to be two
 * different URLs when they both go to the same location. This SEO enhancement
 * prevents penalty for duplicate content by redirecting all incoming links to
 * one or the other.
 *
 * Prevents redirection for feeds, trackbacks, searches, and
 * admin URLs. Does not redirect on non-pretty-permalink-supporting IIS 7+,
 * page/post previews, WP admin, Trackbacks, robots.txt, favicon.ico, searches,
 * or on POST requests.
 *
 * Will also attempt to find the correct link when a user enters a URL that does
 * not exist based on exact WordPress query. Will instead try to parse the URL
 * or query in an attempt to figure the correct page to go to.
 *
 * @since 2.3.0
 *
 * @global WP_Rewrite $wp_rewrite WordPress rewrite component.
 * @global bool       $is_IIS
 * @global WP_Query   $wp_query   WordPress Query object.
 * @global wpdb       $wpdb       WordPress database abstraction object.
 * @global WP         $wp         Current WordPress environment instance.
 *
 * @param string $requested_url Optional. The URL that was requested, used to
 *                              figure if redirect is needed.
 * @param bool   $do_redirect   Optional. Redirect to the new URL.
 * @return string|void The string of the URL, if redirect needed.
 */
function redirect_canonical($requested_url = null, $do_redirect = true)
{
    global $wp_rewrite, $is_IIS, $wp_query, $wpdb, $wp;
    if (isset($_SERVER['REQUEST_METHOD']) && !in_array(strtoupper($_SERVER['REQUEST_METHOD']), array('GET', 'HEAD'), true)) {
        return;
    }
    // If we're not in wp-admin and the post has been published and preview nonce
    // is non-existent or invalid then no need for preview in query.
    if (is_preview() && get_query_var('p') && 'publish' === get_post_status(get_query_var('p'))) {
        if (!isset($_GET['preview_id']) || !isset($_GET['preview_nonce']) || !wp_verify_nonce($_GET['preview_nonce'], 'post_preview_' . (int) $_GET['preview_id'])) {
            $wp_query->is_preview = false;
        }
    }
    if (is_admin() || is_search() || is_preview() || is_trackback() || is_favicon() || $is_IIS && !iis7_supports_permalinks()) {
        return;
    }
    if (!$requested_url && isset($_SERVER['HTTP_HOST'])) {
        // Build the URL in the address bar.
        $requested_url = is_ssl() ? 'https://' : 'http://';
        $requested_url .= $_SERVER['HTTP_HOST'];
        $requested_url .= $_SERVER['REQUEST_URI'];
    }
    $original = parse_url($requested_url);
    if (false === $original) {
        return;
    }
    $redirect = $original;
    $redirect_url = false;
    $redirect_obj = false;
    // Notice fixing.
    if (!isset($redirect['path'])) {
        $redirect['path'] = '';
    }
    if (!isset($redirect['query'])) {
        $redirect['query'] = '';
    }
    /*
     * If the original URL ended with non-breaking spaces, they were almost
     * certainly inserted by accident. Let's remove them, so the reader doesn't
     * see a 404 error with no obvious cause.
     */
    $redirect['path'] = preg_replace('|(%C2%A0)+$|i', '', $redirect['path']);
    // It's not a preview, so remove it from URL.
    if (get_query_var('preview')) {
        $redirect['query'] = remove_query_arg('preview', $redirect['query']);
    }
    $post_id = get_query_var('p');
    if (is_feed() && $post_id) {
        $redirect_url = get_post_comments_feed_link($post_id, get_query_var('feed'));
        $redirect_obj = get_post($post_id);
        if ($redirect_url) {
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type', 'feed'), $redirect_url);
            $redirect['path'] = parse_url($redirect_url, PHP_URL_PATH);
        }
    }
    if (is_singular() && $wp_query->post_count < 1 && $post_id) {
        $vars = $wpdb->get_results($wpdb->prepare("SELECT post_type, post_parent FROM {$wpdb->posts} WHERE ID = %d", $post_id));
        if (!empty($vars[0])) {
            $vars = $vars[0];
            if ('revision' === $vars->post_type && $vars->post_parent > 0) {
                $post_id = $vars->post_parent;
            }
            $redirect_url = get_permalink($post_id);
            $redirect_obj = get_post($post_id);
            if ($redirect_url) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    }
    // These tests give us a WP-generated permalink.
    if (is_404()) {
        // Redirect ?page_id, ?p=, ?attachment_id= to their respective URLs.
        $post_id = max(get_query_var('p'), get_query_var('page_id'), get_query_var('attachment_id'));
        $redirect_post = $post_id ? get_post($post_id) : false;
        if ($redirect_post) {
            $post_type_obj = get_post_type_object($redirect_post->post_type);
            if ($post_type_obj && $post_type_obj->public && 'auto-draft' !== $redirect_post->post_status) {
                $redirect_url = get_permalink($redirect_post);
                $redirect_obj = get_post($redirect_post);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
        $year = get_query_var('year');
        $month = get_query_var('monthnum');
        $day = get_query_var('day');
        if ($year && $month && $day) {
            $date = sprintf('%04d-%02d-%02d', $year, $month, $day);
            if (!wp_checkdate($month, $day, $year, $date)) {
                $redirect_url = get_month_link($year, $month);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum', 'day'), $redirect_url);
            }
        } elseif ($year && $month && $month > 12) {
            $redirect_url = get_year_link($year);
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum'), $redirect_url);
        }
        // Strip off non-existing <!--nextpage--> links from single posts or pages.
        if (get_query_var('page')) {
            $post_id = 0;
            if ($wp_query->queried_object instanceof WP_Post) {
                $post_id = $wp_query->queried_object->ID;
            } elseif ($wp_query->post) {
                $post_id = $wp_query->post->ID;
            }
            if ($post_id) {
                $redirect_url = get_permalink($post_id);
                $redirect_obj = get_post($post_id);
                $redirect['path'] = rtrim($redirect['path'], (int) get_query_var('page') . '/');
                $redirect['query'] = remove_query_arg('page', $redirect['query']);
            }
        }
        if (!$redirect_url) {
            $redirect_url = redirect_guess_404_permalink();
            if ($redirect_url) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('page', 'feed', 'p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    } elseif (is_object($wp_rewrite) && $wp_rewrite->using_permalinks()) {
        // Rewriting of old ?p=X, ?m=2004, ?m=200401, ?m=20040101.
        if (is_attachment() && !array_diff(array_keys($wp->query_vars), array('attachment', 'attachment_id')) && !$redirect_url) {
            if (!empty($_GET['attachment_id'])) {
                $redirect_url = get_attachment_link(get_query_var('attachment_id'));
                $redirect_obj = get_post(get_query_var('attachment_id'));
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('attachment_id', $redirect['query']);
                }
            } else {
                $redirect_url = get_attachment_link();
                $redirect_obj = get_post();
            }
        } elseif (is_single() && !empty($_GET['p']) && !$redirect_url) {
            $redirect_url = get_permalink(get_query_var('p'));
            $redirect_obj = get_post(get_query_var('p'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg(array('p', 'post_type'), $redirect['query']);
            }
        } elseif (is_single() && !empty($_GET['name']) && !$redirect_url) {
            $redirect_url = get_permalink($wp_query->get_queried_object_id());
            $redirect_obj = get_post($wp_query->get_queried_object_id());
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('name', $redirect['query']);
            }
        } elseif (is_page() && !empty($_GET['page_id']) && !$redirect_url) {
            $redirect_url = get_permalink(get_query_var('page_id'));
            $redirect_obj = get_post(get_query_var('page_id'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (is_page() && !is_feed() && !$redirect_url && 'page' === get_option('show_on_front') && get_queried_object_id() === (int) get_option('page_on_front')) {
            $redirect_url = home_url('/');
        } elseif (is_home() && !empty($_GET['page_id']) && !$redirect_url && 'page' === get_option('show_on_front') && get_query_var('page_id') === (int) get_option('page_for_posts')) {
            $redirect_url = get_permalink(get_option('page_for_posts'));
            $redirect_obj = get_post(get_option('page_for_posts'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (!empty($_GET['m']) && (is_year() || is_month() || is_day())) {
            $m = get_query_var('m');
            switch (strlen($m)) {
                case 4:
                    // Yearly.
                    $redirect_url = get_year_link($m);
                    break;
                case 6:
                    // Monthly.
                    $redirect_url = get_month_link(substr($m, 0, 4), substr($m, 4, 2));
                    break;
                case 8:
                    // Daily.
                    $redirect_url = get_day_link(substr($m, 0, 4), substr($m, 4, 2), substr($m, 6, 2));
                    break;
            }
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('m', $redirect['query']);
            }
            // Now moving on to non ?m=X year/month/day links.
        } elseif (is_date()) {
            $year = get_query_var('year');
            $month = get_query_var('monthnum');
            $day = get_query_var('day');
            if (is_day() && $year && $month && !empty($_GET['day'])) {
                $redirect_url = get_day_link($year, $month, $day);
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg(array('year', 'monthnum', 'day'), $redirect['query']);
                }
            } elseif (is_month() && $year && !empty($_GET['monthnum'])) {
                $redirect_url = get_month_link($year, $month);
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg(array('year', 'monthnum'), $redirect['query']);
                }
            } elseif (is_year() && !empty($_GET['year'])) {
                $redirect_url = get_year_link($year);
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('year', $redirect['query']);
                }
            }
        } elseif (is_author() && !empty($_GET['author']) && preg_match('|^[0-9]+$|', $_GET['author'])) {
            $author = get_userdata(get_query_var('author'));
            if (false !== $author && $wpdb->get_var($wpdb->prepare("SELECT ID FROM {$wpdb->posts} WHERE {$wpdb->posts}.post_author = %d AND {$wpdb->posts}.post_status = 'publish' LIMIT 1", $author->ID))) {
                $redirect_url = get_author_posts_url($author->ID, $author->user_nicename);
                $redirect_obj = $author;
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('author', $redirect['query']);
                }
            }
        } elseif (is_category() || is_tag() || is_tax()) {
            // Terms (tags/categories).
            $term_count = 0;
            foreach ($wp_query->tax_query->queried_terms as $tax_query) {
                if (isset($tax_query['terms']) && is_countable($tax_query['terms'])) {
                    $term_count += count($tax_query['terms']);
                }
            }
            $obj = $wp_query->get_queried_object();
            if ($term_count <= 1 && !empty($obj->term_id)) {
                $tax_url = get_term_link((int) $obj->term_id, $obj->taxonomy);
                if ($tax_url && !is_wp_error($tax_url)) {
                    if (!empty($redirect['query'])) {
                        // Strip taxonomy query vars off the URL.
                        $qv_remove = array('term', 'taxonomy');
                        if (is_category()) {
                            $qv_remove[] = 'category_name';
                            $qv_remove[] = 'cat';
                        } elseif (is_tag()) {
                            $qv_remove[] = 'tag';
                            $qv_remove[] = 'tag_id';
                        } else {
                            // Custom taxonomies will have a custom query var, remove those too.
                            $tax_obj = get_taxonomy($obj->taxonomy);
                            if (false !== $tax_obj->query_var) {
                                $qv_remove[] = $tax_obj->query_var;
                            }
                        }
                        $rewrite_vars = array_diff(array_keys($wp_query->query), array_keys($_GET));
                        // Check to see if all the query vars are coming from the rewrite, none are set via $_GET.
                        if (!array_diff($rewrite_vars, array_keys($_GET))) {
                            // Remove all of the per-tax query vars.
                            $redirect['query'] = remove_query_arg($qv_remove, $redirect['query']);
                            // Create the destination URL for this taxonomy.
                            $tax_url = parse_url($tax_url);
                            if (!empty($tax_url['query'])) {
                                // Taxonomy accessible via ?taxonomy=...&term=... or any custom query var.
                                parse_str($tax_url['query'], $query_vars);
                                $redirect['query'] = add_query_arg($query_vars, $redirect['query']);
                            } else {
                                // Taxonomy is accessible via a "pretty URL".
                                $redirect['path'] = $tax_url['path'];
                            }
                        } else {
                            // Some query vars are set via $_GET. Unset those from $_GET that exist via the rewrite.
                            foreach ($qv_remove as $_qv) {
                                if (isset($rewrite_vars[$_qv])) {
                                    $redirect['query'] = remove_query_arg($_qv, $redirect['query']);
                                }
                            }
                        }
                    }
                }
            }
        } elseif (is_single() && strpos($wp_rewrite->permalink_structure, '%category%') !== false) {
            $category_name = get_query_var('category_name');
            if ($category_name) {
                $category = get_category_by_path($category_name);
                if (!$category || is_wp_error($category) || !has_term($category->term_id, 'category', $wp_query->get_queried_object_id())) {
                    $redirect_url = get_permalink($wp_query->get_queried_object_id());
                    $redirect_obj = get_post($wp_query->get_queried_object_id());
                }
            }
        }
        // Post paging.
        if (is_singular() && get_query_var('page')) {
            $page = get_query_var('page');
            if (!$redirect_url) {
                $redirect_url = get_permalink(get_queried_object_id());
                $redirect_obj = get_post(get_queried_object_id());
            }
            if ($page > 1) {
                $redirect_url = trailingslashit($redirect_url);
                if (is_front_page()) {
                    $redirect_url .= user_trailingslashit("{$wp_rewrite->pagination_base}/{$page}", 'paged');
                } else {
                    $redirect_url .= user_trailingslashit($page, 'single_paged');
                }
            }
            $redirect['query'] = remove_query_arg('page', $redirect['query']);
        }
        if (get_query_var('sitemap')) {
            $redirect_url = get_sitemap_url(get_query_var('sitemap'), get_query_var('sitemap-subtype'), get_query_var('paged'));
            $redirect['query'] = remove_query_arg(array('sitemap', 'sitemap-subtype', 'paged'), $redirect['query']);
        } elseif (get_query_var('paged') || is_feed() || get_query_var('cpage')) {
            // Paging and feeds.
            $paged = get_query_var('paged');
            $feed = get_query_var('feed');
            $cpage = get_query_var('cpage');
            while (preg_match("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", $redirect['path']) || preg_match('#/(comments/?)?(feed|rss2?|rdf|atom)(/+)?$#', $redirect['path']) || preg_match("#/{$wp_rewrite->comments_pagination_base}-[0-9]+(/+)?\$#", $redirect['path'])) {
                // Strip off any existing paging.
                $redirect['path'] = preg_replace("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", '/', $redirect['path']);
                // Strip off feed endings.
                $redirect['path'] = preg_replace('#/(comments/?)?(feed|rss2?|rdf|atom)(/+|$)#', '/', $redirect['path']);
                // Strip off any existing comment paging.
                $redirect['path'] = preg_replace("#/{$wp_rewrite->comments_pagination_base}-[0-9]+?(/+)?\$#", '/', $redirect['path']);
            }
            $addl_path = '';
            $default_feed = get_default_feed();
            if (is_feed() && in_array($feed, $wp_rewrite->feeds, true)) {
                $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                if (!is_singular() && get_query_var('withcomments')) {
                    $addl_path .= 'comments/';
                }
                if ('rss' === $default_feed && 'feed' === $feed || 'rss' === $feed) {
                    $format = ('rss2' === $default_feed) ? '' : 'rss2';
                } else {
                    $format = ($default_feed === $feed || 'feed' === $feed) ? '' : $feed;
                }
                $addl_path .= user_trailingslashit('feed/' . $format, 'feed');
                $redirect['query'] = remove_query_arg('feed', $redirect['query']);
            } elseif (is_feed() && 'old' === $feed) {
                $old_feed_files = array('wp-atom.php' => 'atom', 'wp-commentsrss2.php' => 'comments_rss2', 'wp-feed.php' => $default_feed, 'wp-rdf.php' => 'rdf', 'wp-rss.php' => 'rss2', 'wp-rss2.php' => 'rss2');
                if (isset($old_feed_files[basename($redirect['path'])])) {
                    $redirect_url = get_feed_link($old_feed_files[basename($redirect['path'])]);
                    wp_redirect($redirect_url, 301);
                    die;
                }
            }
            if ($paged > 0) {
                $redirect['query'] = remove_query_arg('paged', $redirect['query']);
                if (!is_feed()) {
                    if (!is_single()) {
                        $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                        if ($paged > 1) {
                            $addl_path .= user_trailingslashit("{$wp_rewrite->pagination_base}/{$paged}", 'paged');
                        }
                    }
                } elseif ($paged > 1) {
                    $redirect['query'] = add_query_arg('paged', $paged, $redirect['query']);
                }
            }
            $default_comments_page = get_option('default_comments_page');
            if (get_option('page_comments') && ('newest' === $default_comments_page && $cpage > 0 || 'newest' !== $default_comments_page && $cpage > 1)) {
                $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                $addl_path .= user_trailingslashit($wp_rewrite->comments_pagination_base . '-' . $cpage, 'commentpaged');
                $redirect['query'] = remove_query_arg('cpage', $redirect['query']);
            }
            // Strip off trailing /index.php/.
            $redirect['path'] = preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/?$|', '/', $redirect['path']);
            $redirect['path'] = user_trailingslashit($redirect['path']);
            if (!empty($addl_path) && $wp_rewrite->using_index_permalinks() && strpos($redirect['path'], '/' . $wp_rewrite->index . '/') === false) {
                $redirect['path'] = trailingslashit($redirect['path']) . $wp_rewrite->index . '/';
            }
            if (!empty($addl_path)) {
                $redirect['path'] = trailingslashit($redirect['path']) . $addl_path;
            }
            $redirect_url = $redirect['scheme'] . '://' . $redirect['host'] . $redirect['path'];
        }
        if ('wp-register.php' === basename($redirect['path'])) {
            if (is_multisite()) {
                /** This filter is documented in wp-login.php */
                $redirect_url = apply_filters('wp_signup_location', network_site_url('wp-signup.php'));
            } else {
                $redirect_url = wp_registration_url();
            }
            wp_redirect($redirect_url, 301);
            die;
        }
    }
    $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    // Tack on any additional query vars.
    if ($redirect_url && !empty($redirect['query'])) {
        parse_str($redirect['query'], $_parsed_query);
        $redirect = parse_url($redirect_url);
        if (!empty($_parsed_query['name']) && !empty($redirect['query'])) {
            parse_str($redirect['query'], $_parsed_redirect_query);
            if (empty($_parsed_redirect_query['name'])) {
                unset($_parsed_query['name']);
            }
        }
        $_parsed_query = array_combine(rawurlencode_deep(array_keys($_parsed_query)), rawurlencode_deep(array_values($_parsed_query)));
        $redirect_url = add_query_arg($_parsed_query, $redirect_url);
    }
    if ($redirect_url) {
        $redirect = parse_url($redirect_url);
    }
    // www.example.com vs. example.com
    $user_home = parse_url(home_url());
    if (!empty($user_home['host'])) {
        $redirect['host'] = $user_home['host'];
    }
    if (empty($user_home['path'])) {
        $user_home['path'] = '/';
    }
    // Handle ports.
    if (!empty($user_home['port'])) {
        $redirect['port'] = $user_home['port'];
    } else {
        unset($redirect['port']);
    }
    // Trailing /index.php.
    $redirect['path'] = preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/*?$|', '/', $redirect['path']);
    $punctuation_pattern = implode('|', array_map('preg_quote', array(
        ' ',
        '%20',
        // Space.
        '!',
        '%21',
        // Exclamation mark.
        '"',
        '%22',
        // Double quote.
        "'",
        '%27',
        // Single quote.
        '(',
        '%28',
        // Opening bracket.
        ')',
        '%29',
        // Closing bracket.
        ',',
        '%2C',
        // Comma.
        '.',
        '%2E',
        // Period.
        ';',
        '%3B',
        // Semicolon.
        '{',
        '%7B',
        // Opening curly bracket.
        '}',
        '%7D',
        // Closing curly bracket.
        '%E2%80%9C',
        // Opening curly quote.
        '%E2%80%9D',
    )));
    // Remove trailing spaces and end punctuation from the path.
    $redirect['path'] = preg_replace("#({$punctuation_pattern})+\$#", '', $redirect['path']);
    if (!empty($redirect['query'])) {
        // Remove trailing spaces and end punctuation from certain terminating query string args.
        $redirect['query'] = preg_replace("#((^|&)(p|page_id|cat|tag)=[^&]*?)({$punctuation_pattern})+\$#", '$1', $redirect['query']);
        // Clean up empty query strings.
        $redirect['query'] = trim(preg_replace('#(^|&)(p|page_id|cat|tag)=?(&|$)#', '&', $redirect['query']), '&');
        // Redirect obsolete feeds.
        $redirect['query'] = preg_replace('#(^|&)feed=rss(&|$)#', '$1feed=rss2$2', $redirect['query']);
        // Remove redundant leading ampersands.
        $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    }
    // Strip /index.php/ when we're not using PATHINFO permalinks.
    if (!$wp_rewrite->using_index_permalinks()) {
        $redirect['path'] = str_replace('/' . $wp_rewrite->index . '/', '/', $redirect['path']);
    }
    // Trailing slashes.
    if (is_object($wp_rewrite) && $wp_rewrite->using_permalinks() && !is_404() && (!is_front_page() || is_front_page() && get_query_var('paged') > 1)) {
        $user_ts_type = '';
        if (get_query_var('paged') > 0) {
            $user_ts_type = 'paged';
        } else {
            foreach (array('single', 'category', 'page', 'day', 'month', 'year', 'home') as $type) {
                $func = 'is_' . $type;
                if (call_user_func($func)) {
                    $user_ts_type = $type;
                    break;
                }
            }
        }
        $redirect['path'] = user_trailingslashit($redirect['path'], $user_ts_type);
    } elseif (is_front_page()) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Remove trailing slash for robots.txt or sitemap requests.
    if (is_robots() || !empty(get_query_var('sitemap')) || !empty(get_query_var('sitemap-stylesheet'))) {
        $redirect['path'] = untrailingslashit($redirect['path']);
    }
    // Strip multiple slashes out of the URL.
    if (strpos($redirect['path'], '//') > -1) {
        $redirect['path'] = preg_replace('|/+|', '/', $redirect['path']);
    }
    // Always trailing slash the Front Page URL.
    if (trailingslashit($redirect['path']) === trailingslashit($user_home['path'])) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    $original_host_low = strtolower($original['host']);
    $redirect_host_low = strtolower($redirect['host']);
    // Ignore differences in host capitalization, as this can lead to infinite redirects.
    // Only redirect no-www <=> yes-www.
    if ($original_host_low === $redirect_host_low || 'www.' . $original_host_low !== $redirect_host_low && 'www.' . $redirect_host_low !== $original_host_low) {
        $redirect['host'] = $original['host'];
    }
    $compare_original = array($original['host'], $original['path']);
    if (!empty($original['port'])) {
        $compare_original[] = $original['port'];
    }
    if (!empty($original['query'])) {
        $compare_original[] = $original['query'];
    }
    $compare_redirect = array($redirect['host'], $redirect['path']);
    if (!empty($redirect['port'])) {
        $compare_redirect[] = $redirect['port'];
    }
    if (!empty($redirect['query'])) {
        $compare_redirect[] = $redirect['query'];
    }
    if ($compare_original !== $compare_redirect) {
        $redirect_url = $redirect['scheme'] . '://' . $redirect['host'];
        if (!empty($redirect['port'])) {
            $redirect_url .= ':' . $redirect['port'];
        }
        $redirect_url .= $redirect['path'];
        if (!empty($redirect['query'])) {
            $redirect_url .= '?' . $redirect['query'];
        }
    }
    if (!$redirect_url || $redirect_url === $requested_url) {
        return;
    }
    // Hex encoded octets are case-insensitive.
    if (false !== strpos($requested_url, '%')) {
        if (!function_exists('lowercase_octets')) {
            /**
             * Converts the first hex-encoded octet match to lowercase.
             *
             * @since 3.1.0
             * @ignore
             *
             * @param array $matches Hex-encoded octet matches for the requested URL.
             * @return string Lowercased version of the first match.
             */
            function lowercase_octets($matches)
            {
                return strtolower($matches[0]);
            }
        }
        $requested_url = preg_replace_callback('|%[a-fA-F0-9][a-fA-F0-9]|', 'lowercase_octets', $requested_url);
    }
    if ($redirect_obj instanceof WP_Post) {
        $post_status_obj = get_post_status_object(get_post_status($redirect_obj));
        /*
         * Unset the redirect object and URL if they are not readable by the user.
         * This condition is a little confusing as the condition needs to pass if
         * the post is not readable by the user. That's why there are ! (not) conditions
         * throughout.
         */
        if (!($post_status_obj->private && current_user_can('read_post', $redirect_obj->ID)) && !is_post_publicly_viewable($redirect_obj)) {
            $redirect_obj = false;
            $redirect_url = false;
        }
    }
    /**
     * Filters the canonical redirect URL.
     *
     * Returning false to this filter will cancel the redirect.
     *
     * @since 2.3.0
     *
     * @param string $redirect_url  The redirect URL.
     * @param string $requested_url The requested URL.
     */
    $redirect_url = apply_filters('redirect_canonical', $redirect_url, $requested_url);
    // Yes, again -- in case the filter aborted the request.
    if (!$redirect_url || strip_fragment_from_url($redirect_url) === strip_fragment_from_url($requested_url)) {
        return;
    }
    if ($do_redirect) {
        // Protect against chained redirects.
        if (!redirect_canonical($redirect_url, false)) {
            wp_redirect($redirect_url, 301);
            exit;
        } else {
            // Debug.
            // die("1: $redirect_url<br />2: " . redirect_canonical( $redirect_url, false ) );
            return;
        }
    } else {
        return $redirect_url;
    }
}

WordPress Version: 5.7

/**
 * Canonical API to handle WordPress Redirecting
 *
 * Based on "Permalink Redirect" from Scott Yang and "Enforce www. Preference"
 * by Mark Jaquith
 *
 * @package WordPress
 * @since 2.3.0
 */
/**
 * Redirects incoming links to the proper URL based on the site url.
 *
 * Search engines consider www.somedomain.com and somedomain.com to be two
 * different URLs when they both go to the same location. This SEO enhancement
 * prevents penalty for duplicate content by redirecting all incoming links to
 * one or the other.
 *
 * Prevents redirection for feeds, trackbacks, searches, and
 * admin URLs. Does not redirect on non-pretty-permalink-supporting IIS 7+,
 * page/post previews, WP admin, Trackbacks, robots.txt, favicon.ico, searches,
 * or on POST requests.
 *
 * Will also attempt to find the correct link when a user enters a URL that does
 * not exist based on exact WordPress query. Will instead try to parse the URL
 * or query in an attempt to figure the correct page to go to.
 *
 * @since 2.3.0
 *
 * @global WP_Rewrite $wp_rewrite WordPress rewrite component.
 * @global bool       $is_IIS
 * @global WP_Query   $wp_query   WordPress Query object.
 * @global wpdb       $wpdb       WordPress database abstraction object.
 * @global WP         $wp         Current WordPress environment instance.
 *
 * @param string $requested_url Optional. The URL that was requested, used to
 *                              figure if redirect is needed.
 * @param bool   $do_redirect   Optional. Redirect to the new URL.
 * @return string|void The string of the URL, if redirect needed.
 */
function redirect_canonical($requested_url = null, $do_redirect = true)
{
    global $wp_rewrite, $is_IIS, $wp_query, $wpdb, $wp;
    if (isset($_SERVER['REQUEST_METHOD']) && !in_array(strtoupper($_SERVER['REQUEST_METHOD']), array('GET', 'HEAD'), true)) {
        return;
    }
    // If we're not in wp-admin and the post has been published and preview nonce
    // is non-existent or invalid then no need for preview in query.
    if (is_preview() && get_query_var('p') && 'publish' === get_post_status(get_query_var('p'))) {
        if (!isset($_GET['preview_id']) || !isset($_GET['preview_nonce']) || !wp_verify_nonce($_GET['preview_nonce'], 'post_preview_' . (int) $_GET['preview_id'])) {
            $wp_query->is_preview = false;
        }
    }
    if (is_admin() || is_search() || is_preview() || is_trackback() || is_favicon() || $is_IIS && !iis7_supports_permalinks()) {
        return;
    }
    if (!$requested_url && isset($_SERVER['HTTP_HOST'])) {
        // Build the URL in the address bar.
        $requested_url = is_ssl() ? 'https://' : 'http://';
        $requested_url .= $_SERVER['HTTP_HOST'];
        $requested_url .= $_SERVER['REQUEST_URI'];
    }
    $original = parse_url($requested_url);
    if (false === $original) {
        return;
    }
    $redirect = $original;
    $redirect_url = false;
    $redirect_obj = false;
    // Notice fixing.
    if (!isset($redirect['path'])) {
        $redirect['path'] = '';
    }
    if (!isset($redirect['query'])) {
        $redirect['query'] = '';
    }
    /*
     * If the original URL ended with non-breaking spaces, they were almost
     * certainly inserted by accident. Let's remove them, so the reader doesn't
     * see a 404 error with no obvious cause.
     */
    $redirect['path'] = preg_replace('|(%C2%A0)+$|i', '', $redirect['path']);
    // It's not a preview, so remove it from URL.
    if (get_query_var('preview')) {
        $redirect['query'] = remove_query_arg('preview', $redirect['query']);
    }
    $post_id = get_query_var('p');
    if (is_feed() && $post_id) {
        $redirect_url = get_post_comments_feed_link($post_id, get_query_var('feed'));
        $redirect_obj = get_post($post_id);
        if ($redirect_url) {
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type', 'feed'), $redirect_url);
            $redirect['path'] = parse_url($redirect_url, PHP_URL_PATH);
        }
    }
    if (is_singular() && $wp_query->post_count < 1 && $post_id) {
        $vars = $wpdb->get_results($wpdb->prepare("SELECT post_type, post_parent FROM {$wpdb->posts} WHERE ID = %d", $post_id));
        if (!empty($vars[0])) {
            $vars = $vars[0];
            if ('revision' === $vars->post_type && $vars->post_parent > 0) {
                $post_id = $vars->post_parent;
            }
            $redirect_url = get_permalink($post_id);
            $redirect_obj = get_post($post_id);
            if ($redirect_url) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    }
    // These tests give us a WP-generated permalink.
    if (is_404()) {
        // Redirect ?page_id, ?p=, ?attachment_id= to their respective URLs.
        $post_id = max(get_query_var('p'), get_query_var('page_id'), get_query_var('attachment_id'));
        $redirect_post = $post_id ? get_post($post_id) : false;
        if ($redirect_post) {
            $post_type_obj = get_post_type_object($redirect_post->post_type);
            if ($post_type_obj && $post_type_obj->public && 'auto-draft' !== $redirect_post->post_status) {
                $redirect_url = get_permalink($redirect_post);
                $redirect_obj = get_post($redirect_post);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
        $year = get_query_var('year');
        $month = get_query_var('monthnum');
        $day = get_query_var('day');
        if ($year && $month && $day) {
            $date = sprintf('%04d-%02d-%02d', $year, $month, $day);
            if (!wp_checkdate($month, $day, $year, $date)) {
                $redirect_url = get_month_link($year, $month);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum', 'day'), $redirect_url);
            }
        } elseif ($year && $month && $month > 12) {
            $redirect_url = get_year_link($year);
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum'), $redirect_url);
        }
        // Strip off non-existing <!--nextpage--> links from single posts or pages.
        if (get_query_var('page')) {
            $post_id = 0;
            if ($wp_query->queried_object instanceof WP_Post) {
                $post_id = $wp_query->queried_object->ID;
            } elseif ($wp_query->post) {
                $post_id = $wp_query->post->ID;
            }
            if ($post_id) {
                $redirect_url = get_permalink($post_id);
                $redirect_obj = get_post($post_id);
                $redirect['path'] = rtrim($redirect['path'], (int) get_query_var('page') . '/');
                $redirect['query'] = remove_query_arg('page', $redirect['query']);
            }
        }
        if (!$redirect_url) {
            $redirect_url = redirect_guess_404_permalink();
            if ($redirect_url) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('page', 'feed', 'p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    } elseif (is_object($wp_rewrite) && $wp_rewrite->using_permalinks()) {
        // Rewriting of old ?p=X, ?m=2004, ?m=200401, ?m=20040101.
        if (is_attachment() && !array_diff(array_keys($wp->query_vars), array('attachment', 'attachment_id')) && !$redirect_url) {
            if (!empty($_GET['attachment_id'])) {
                $redirect_url = get_attachment_link(get_query_var('attachment_id'));
                $redirect_obj = get_post(get_query_var('attachment_id'));
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('attachment_id', $redirect['query']);
                }
            } else {
                $redirect_url = get_attachment_link();
                $redirect_obj = get_post();
            }
        } elseif (is_single() && !empty($_GET['p']) && !$redirect_url) {
            $redirect_url = get_permalink(get_query_var('p'));
            $redirect_obj = get_post(get_query_var('p'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg(array('p', 'post_type'), $redirect['query']);
            }
        } elseif (is_single() && !empty($_GET['name']) && !$redirect_url) {
            $redirect_url = get_permalink($wp_query->get_queried_object_id());
            $redirect_obj = get_post($wp_query->get_queried_object_id());
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('name', $redirect['query']);
            }
        } elseif (is_page() && !empty($_GET['page_id']) && !$redirect_url) {
            $redirect_url = get_permalink(get_query_var('page_id'));
            $redirect_obj = get_post(get_query_var('page_id'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (is_page() && !is_feed() && !$redirect_url && 'page' === get_option('show_on_front') && get_queried_object_id() === (int) get_option('page_on_front')) {
            $redirect_url = home_url('/');
        } elseif (is_home() && !empty($_GET['page_id']) && !$redirect_url && 'page' === get_option('show_on_front') && get_query_var('page_id') === (int) get_option('page_for_posts')) {
            $redirect_url = get_permalink(get_option('page_for_posts'));
            $redirect_obj = get_post(get_option('page_for_posts'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (!empty($_GET['m']) && (is_year() || is_month() || is_day())) {
            $m = get_query_var('m');
            switch (strlen($m)) {
                case 4:
                    // Yearly.
                    $redirect_url = get_year_link($m);
                    break;
                case 6:
                    // Monthly.
                    $redirect_url = get_month_link(substr($m, 0, 4), substr($m, 4, 2));
                    break;
                case 8:
                    // Daily.
                    $redirect_url = get_day_link(substr($m, 0, 4), substr($m, 4, 2), substr($m, 6, 2));
                    break;
            }
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('m', $redirect['query']);
            }
            // Now moving on to non ?m=X year/month/day links.
        } elseif (is_date()) {
            $year = get_query_var('year');
            $month = get_query_var('monthnum');
            $day = get_query_var('day');
            if (is_day() && $year && $month && !empty($_GET['day'])) {
                $redirect_url = get_day_link($year, $month, $day);
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg(array('year', 'monthnum', 'day'), $redirect['query']);
                }
            } elseif (is_month() && $year && !empty($_GET['monthnum'])) {
                $redirect_url = get_month_link($year, $month);
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg(array('year', 'monthnum'), $redirect['query']);
                }
            } elseif (is_year() && !empty($_GET['year'])) {
                $redirect_url = get_year_link($year);
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('year', $redirect['query']);
                }
            }
        } elseif (is_author() && !empty($_GET['author']) && preg_match('|^[0-9]+$|', $_GET['author'])) {
            $author = get_userdata(get_query_var('author'));
            if (false !== $author && $wpdb->get_var($wpdb->prepare("SELECT ID FROM {$wpdb->posts} WHERE {$wpdb->posts}.post_author = %d AND {$wpdb->posts}.post_status = 'publish' LIMIT 1", $author->ID))) {
                $redirect_url = get_author_posts_url($author->ID, $author->user_nicename);
                $redirect_obj = $author;
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('author', $redirect['query']);
                }
            }
        } elseif (is_category() || is_tag() || is_tax()) {
            // Terms (tags/categories).
            $term_count = 0;
            foreach ($wp_query->tax_query->queried_terms as $tax_query) {
                $term_count += count($tax_query['terms']);
            }
            $obj = $wp_query->get_queried_object();
            if ($term_count <= 1 && !empty($obj->term_id)) {
                $tax_url = get_term_link((int) $obj->term_id, $obj->taxonomy);
                if ($tax_url && !is_wp_error($tax_url)) {
                    if (!empty($redirect['query'])) {
                        // Strip taxonomy query vars off the URL.
                        $qv_remove = array('term', 'taxonomy');
                        if (is_category()) {
                            $qv_remove[] = 'category_name';
                            $qv_remove[] = 'cat';
                        } elseif (is_tag()) {
                            $qv_remove[] = 'tag';
                            $qv_remove[] = 'tag_id';
                        } else {
                            // Custom taxonomies will have a custom query var, remove those too.
                            $tax_obj = get_taxonomy($obj->taxonomy);
                            if (false !== $tax_obj->query_var) {
                                $qv_remove[] = $tax_obj->query_var;
                            }
                        }
                        $rewrite_vars = array_diff(array_keys($wp_query->query), array_keys($_GET));
                        // Check to see if all the query vars are coming from the rewrite, none are set via $_GET.
                        if (!array_diff($rewrite_vars, array_keys($_GET))) {
                            // Remove all of the per-tax query vars.
                            $redirect['query'] = remove_query_arg($qv_remove, $redirect['query']);
                            // Create the destination URL for this taxonomy.
                            $tax_url = parse_url($tax_url);
                            if (!empty($tax_url['query'])) {
                                // Taxonomy accessible via ?taxonomy=...&term=... or any custom query var.
                                parse_str($tax_url['query'], $query_vars);
                                $redirect['query'] = add_query_arg($query_vars, $redirect['query']);
                            } else {
                                // Taxonomy is accessible via a "pretty URL".
                                $redirect['path'] = $tax_url['path'];
                            }
                        } else {
                            // Some query vars are set via $_GET. Unset those from $_GET that exist via the rewrite.
                            foreach ($qv_remove as $_qv) {
                                if (isset($rewrite_vars[$_qv])) {
                                    $redirect['query'] = remove_query_arg($_qv, $redirect['query']);
                                }
                            }
                        }
                    }
                }
            }
        } elseif (is_single() && strpos($wp_rewrite->permalink_structure, '%category%') !== false) {
            $category_name = get_query_var('category_name');
            if ($category_name) {
                $category = get_category_by_path($category_name);
                if (!$category || is_wp_error($category) || !has_term($category->term_id, 'category', $wp_query->get_queried_object_id())) {
                    $redirect_url = get_permalink($wp_query->get_queried_object_id());
                    $redirect_obj = get_post($wp_query->get_queried_object_id());
                }
            }
        }
        // Post paging.
        if (is_singular() && get_query_var('page')) {
            $page = get_query_var('page');
            if (!$redirect_url) {
                $redirect_url = get_permalink(get_queried_object_id());
                $redirect_obj = get_post(get_queried_object_id());
            }
            if ($page > 1) {
                $redirect_url = trailingslashit($redirect_url);
                if (is_front_page()) {
                    $redirect_url .= user_trailingslashit("{$wp_rewrite->pagination_base}/{$page}", 'paged');
                } else {
                    $redirect_url .= user_trailingslashit($page, 'single_paged');
                }
            }
            $redirect['query'] = remove_query_arg('page', $redirect['query']);
        }
        if (get_query_var('sitemap')) {
            $redirect_url = get_sitemap_url(get_query_var('sitemap'), get_query_var('sitemap-subtype'), get_query_var('paged'));
            $redirect['query'] = remove_query_arg(array('sitemap', 'sitemap-subtype', 'paged'), $redirect['query']);
        } elseif (get_query_var('paged') || is_feed() || get_query_var('cpage')) {
            // Paging and feeds.
            $paged = get_query_var('paged');
            $feed = get_query_var('feed');
            $cpage = get_query_var('cpage');
            while (preg_match("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", $redirect['path']) || preg_match('#/(comments/?)?(feed|rss2?|rdf|atom)(/+)?$#', $redirect['path']) || preg_match("#/{$wp_rewrite->comments_pagination_base}-[0-9]+(/+)?\$#", $redirect['path'])) {
                // Strip off any existing paging.
                $redirect['path'] = preg_replace("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", '/', $redirect['path']);
                // Strip off feed endings.
                $redirect['path'] = preg_replace('#/(comments/?)?(feed|rss2?|rdf|atom)(/+|$)#', '/', $redirect['path']);
                // Strip off any existing comment paging.
                $redirect['path'] = preg_replace("#/{$wp_rewrite->comments_pagination_base}-[0-9]+?(/+)?\$#", '/', $redirect['path']);
            }
            $addl_path = '';
            $default_feed = get_default_feed();
            if (is_feed() && in_array($feed, $wp_rewrite->feeds, true)) {
                $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                if (!is_singular() && get_query_var('withcomments')) {
                    $addl_path .= 'comments/';
                }
                if ('rss' === $default_feed && 'feed' === $feed || 'rss' === $feed) {
                    $format = ('rss2' === $default_feed) ? '' : 'rss2';
                } else {
                    $format = ($default_feed === $feed || 'feed' === $feed) ? '' : $feed;
                }
                $addl_path .= user_trailingslashit('feed/' . $format, 'feed');
                $redirect['query'] = remove_query_arg('feed', $redirect['query']);
            } elseif (is_feed() && 'old' === $feed) {
                $old_feed_files = array('wp-atom.php' => 'atom', 'wp-commentsrss2.php' => 'comments_rss2', 'wp-feed.php' => $default_feed, 'wp-rdf.php' => 'rdf', 'wp-rss.php' => 'rss2', 'wp-rss2.php' => 'rss2');
                if (isset($old_feed_files[basename($redirect['path'])])) {
                    $redirect_url = get_feed_link($old_feed_files[basename($redirect['path'])]);
                    wp_redirect($redirect_url, 301);
                    die;
                }
            }
            if ($paged > 0) {
                $redirect['query'] = remove_query_arg('paged', $redirect['query']);
                if (!is_feed()) {
                    if (!is_single()) {
                        $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                        if ($paged > 1) {
                            $addl_path .= user_trailingslashit("{$wp_rewrite->pagination_base}/{$paged}", 'paged');
                        }
                    }
                } elseif ($paged > 1) {
                    $redirect['query'] = add_query_arg('paged', $paged, $redirect['query']);
                }
            }
            $default_comments_page = get_option('default_comments_page');
            if (get_option('page_comments') && ('newest' === $default_comments_page && $cpage > 0 || 'newest' !== $default_comments_page && $cpage > 1)) {
                $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                $addl_path .= user_trailingslashit($wp_rewrite->comments_pagination_base . '-' . $cpage, 'commentpaged');
                $redirect['query'] = remove_query_arg('cpage', $redirect['query']);
            }
            // Strip off trailing /index.php/.
            $redirect['path'] = preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/?$|', '/', $redirect['path']);
            $redirect['path'] = user_trailingslashit($redirect['path']);
            if (!empty($addl_path) && $wp_rewrite->using_index_permalinks() && strpos($redirect['path'], '/' . $wp_rewrite->index . '/') === false) {
                $redirect['path'] = trailingslashit($redirect['path']) . $wp_rewrite->index . '/';
            }
            if (!empty($addl_path)) {
                $redirect['path'] = trailingslashit($redirect['path']) . $addl_path;
            }
            $redirect_url = $redirect['scheme'] . '://' . $redirect['host'] . $redirect['path'];
        }
        if ('wp-register.php' === basename($redirect['path'])) {
            if (is_multisite()) {
                /** This filter is documented in wp-login.php */
                $redirect_url = apply_filters('wp_signup_location', network_site_url('wp-signup.php'));
            } else {
                $redirect_url = wp_registration_url();
            }
            wp_redirect($redirect_url, 301);
            die;
        }
    }
    $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    // Tack on any additional query vars.
    if ($redirect_url && !empty($redirect['query'])) {
        parse_str($redirect['query'], $_parsed_query);
        $redirect = parse_url($redirect_url);
        if (!empty($_parsed_query['name']) && !empty($redirect['query'])) {
            parse_str($redirect['query'], $_parsed_redirect_query);
            if (empty($_parsed_redirect_query['name'])) {
                unset($_parsed_query['name']);
            }
        }
        $_parsed_query = array_combine(rawurlencode_deep(array_keys($_parsed_query)), rawurlencode_deep(array_values($_parsed_query)));
        $redirect_url = add_query_arg($_parsed_query, $redirect_url);
    }
    if ($redirect_url) {
        $redirect = parse_url($redirect_url);
    }
    // www.example.com vs. example.com
    $user_home = parse_url(home_url());
    if (!empty($user_home['host'])) {
        $redirect['host'] = $user_home['host'];
    }
    if (empty($user_home['path'])) {
        $user_home['path'] = '/';
    }
    // Handle ports.
    if (!empty($user_home['port'])) {
        $redirect['port'] = $user_home['port'];
    } else {
        unset($redirect['port']);
    }
    // Trailing /index.php.
    $redirect['path'] = preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/*?$|', '/', $redirect['path']);
    $punctuation_pattern = implode('|', array_map('preg_quote', array(
        ' ',
        '%20',
        // Space.
        '!',
        '%21',
        // Exclamation mark.
        '"',
        '%22',
        // Double quote.
        "'",
        '%27',
        // Single quote.
        '(',
        '%28',
        // Opening bracket.
        ')',
        '%29',
        // Closing bracket.
        ',',
        '%2C',
        // Comma.
        '.',
        '%2E',
        // Period.
        ';',
        '%3B',
        // Semicolon.
        '{',
        '%7B',
        // Opening curly bracket.
        '}',
        '%7D',
        // Closing curly bracket.
        '%E2%80%9C',
        // Opening curly quote.
        '%E2%80%9D',
    )));
    // Remove trailing spaces and end punctuation from the path.
    $redirect['path'] = preg_replace("#({$punctuation_pattern})+\$#", '', $redirect['path']);
    if (!empty($redirect['query'])) {
        // Remove trailing spaces and end punctuation from certain terminating query string args.
        $redirect['query'] = preg_replace("#((^|&)(p|page_id|cat|tag)=[^&]*?)({$punctuation_pattern})+\$#", '$1', $redirect['query']);
        // Clean up empty query strings.
        $redirect['query'] = trim(preg_replace('#(^|&)(p|page_id|cat|tag)=?(&|$)#', '&', $redirect['query']), '&');
        // Redirect obsolete feeds.
        $redirect['query'] = preg_replace('#(^|&)feed=rss(&|$)#', '$1feed=rss2$2', $redirect['query']);
        // Remove redundant leading ampersands.
        $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    }
    // Strip /index.php/ when we're not using PATHINFO permalinks.
    if (!$wp_rewrite->using_index_permalinks()) {
        $redirect['path'] = str_replace('/' . $wp_rewrite->index . '/', '/', $redirect['path']);
    }
    // Trailing slashes.
    if (is_object($wp_rewrite) && $wp_rewrite->using_permalinks() && !is_404() && (!is_front_page() || is_front_page() && get_query_var('paged') > 1)) {
        $user_ts_type = '';
        if (get_query_var('paged') > 0) {
            $user_ts_type = 'paged';
        } else {
            foreach (array('single', 'category', 'page', 'day', 'month', 'year', 'home') as $type) {
                $func = 'is_' . $type;
                if (call_user_func($func)) {
                    $user_ts_type = $type;
                    break;
                }
            }
        }
        $redirect['path'] = user_trailingslashit($redirect['path'], $user_ts_type);
    } elseif (is_front_page()) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Remove trailing slash for robots.txt or sitemap requests.
    if (is_robots() || !empty(get_query_var('sitemap')) || !empty(get_query_var('sitemap-stylesheet'))) {
        $redirect['path'] = untrailingslashit($redirect['path']);
    }
    // Strip multiple slashes out of the URL.
    if (strpos($redirect['path'], '//') > -1) {
        $redirect['path'] = preg_replace('|/+|', '/', $redirect['path']);
    }
    // Always trailing slash the Front Page URL.
    if (trailingslashit($redirect['path']) === trailingslashit($user_home['path'])) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    $original_host_low = strtolower($original['host']);
    $redirect_host_low = strtolower($redirect['host']);
    // Ignore differences in host capitalization, as this can lead to infinite redirects.
    // Only redirect no-www <=> yes-www.
    if ($original_host_low === $redirect_host_low || 'www.' . $original_host_low !== $redirect_host_low && 'www.' . $redirect_host_low !== $original_host_low) {
        $redirect['host'] = $original['host'];
    }
    $compare_original = array($original['host'], $original['path']);
    if (!empty($original['port'])) {
        $compare_original[] = $original['port'];
    }
    if (!empty($original['query'])) {
        $compare_original[] = $original['query'];
    }
    $compare_redirect = array($redirect['host'], $redirect['path']);
    if (!empty($redirect['port'])) {
        $compare_redirect[] = $redirect['port'];
    }
    if (!empty($redirect['query'])) {
        $compare_redirect[] = $redirect['query'];
    }
    if ($compare_original !== $compare_redirect) {
        $redirect_url = $redirect['scheme'] . '://' . $redirect['host'];
        if (!empty($redirect['port'])) {
            $redirect_url .= ':' . $redirect['port'];
        }
        $redirect_url .= $redirect['path'];
        if (!empty($redirect['query'])) {
            $redirect_url .= '?' . $redirect['query'];
        }
    }
    if (!$redirect_url || $redirect_url === $requested_url) {
        return;
    }
    // Hex encoded octets are case-insensitive.
    if (false !== strpos($requested_url, '%')) {
        if (!function_exists('lowercase_octets')) {
            /**
             * Converts the first hex-encoded octet match to lowercase.
             *
             * @since 3.1.0
             * @ignore
             *
             * @param array $matches Hex-encoded octet matches for the requested URL.
             * @return string Lowercased version of the first match.
             */
            function lowercase_octets($matches)
            {
                return strtolower($matches[0]);
            }
        }
        $requested_url = preg_replace_callback('|%[a-fA-F0-9][a-fA-F0-9]|', 'lowercase_octets', $requested_url);
    }
    if ($redirect_obj instanceof WP_Post) {
        $post_status_obj = get_post_status_object(get_post_status($redirect_obj));
        /*
         * Unset the redirect object and URL if they are not readable by the user.
         * This condition is a little confusing as the condition needs to pass if
         * the post is not readable by the user. That's why there are ! (not) conditions
         * throughout.
         */
        if (!($post_status_obj->private && current_user_can('read_post', $redirect_obj->ID)) && !is_post_publicly_viewable($redirect_obj)) {
            $redirect_obj = false;
            $redirect_url = false;
        }
    }
    /**
     * Filters the canonical redirect URL.
     *
     * Returning false to this filter will cancel the redirect.
     *
     * @since 2.3.0
     *
     * @param string $redirect_url  The redirect URL.
     * @param string $requested_url The requested URL.
     */
    $redirect_url = apply_filters('redirect_canonical', $redirect_url, $requested_url);
    // Yes, again -- in case the filter aborted the request.
    if (!$redirect_url || strip_fragment_from_url($redirect_url) === strip_fragment_from_url($requested_url)) {
        return;
    }
    if ($do_redirect) {
        // Protect against chained redirects.
        if (!redirect_canonical($redirect_url, false)) {
            wp_redirect($redirect_url, 301);
            exit;
        } else {
            // Debug.
            // die("1: $redirect_url<br />2: " . redirect_canonical( $redirect_url, false ) );
            return;
        }
    } else {
        return $redirect_url;
    }
}

WordPress Version: 5.1

/**
 * Canonical API to handle WordPress Redirecting
 *
 * Based on "Permalink Redirect" from Scott Yang and "Enforce www. Preference"
 * by Mark Jaquith
 *
 * @package WordPress
 * @since 2.3.0
 */
/**
 * Redirects incoming links to the proper URL based on the site url.
 *
 * Search engines consider www.somedomain.com and somedomain.com to be two
 * different URLs when they both go to the same location. This SEO enhancement
 * prevents penalty for duplicate content by redirecting all incoming links to
 * one or the other.
 *
 * Prevents redirection for feeds, trackbacks, searches, and
 * admin URLs. Does not redirect on non-pretty-permalink-supporting IIS 7+,
 * page/post previews, WP admin, Trackbacks, robots.txt, favicon.ico, searches,
 * or on POST requests.
 *
 * Will also attempt to find the correct link when a user enters a URL that does
 * not exist based on exact WordPress query. Will instead try to parse the URL
 * or query in an attempt to figure the correct page to go to.
 *
 * @since 2.3.0
 *
 * @global WP_Rewrite $wp_rewrite WordPress rewrite component.
 * @global bool       $is_IIS
 * @global WP_Query   $wp_query   WordPress Query object.
 * @global wpdb       $wpdb       WordPress database abstraction object.
 * @global WP         $wp         Current WordPress environment instance.
 *
 * @param string $requested_url Optional. The URL that was requested, used to
 *                              figure if redirect is needed.
 * @param bool   $do_redirect   Optional. Redirect to the new URL.
 * @return string|void The string of the URL, if redirect needed.
 */
function redirect_canonical($requested_url = null, $do_redirect = true)
{
    global $wp_rewrite, $is_IIS, $wp_query, $wpdb, $wp;
    if (isset($_SERVER['REQUEST_METHOD']) && !in_array(strtoupper($_SERVER['REQUEST_METHOD']), array('GET', 'HEAD'), true)) {
        return;
    }
    // If we're not in wp-admin and the post has been published and preview nonce
    // is non-existent or invalid then no need for preview in query.
    if (is_preview() && get_query_var('p') && 'publish' === get_post_status(get_query_var('p'))) {
        if (!isset($_GET['preview_id']) || !isset($_GET['preview_nonce']) || !wp_verify_nonce($_GET['preview_nonce'], 'post_preview_' . (int) $_GET['preview_id'])) {
            $wp_query->is_preview = false;
        }
    }
    if (is_admin() || is_search() || is_preview() || is_trackback() || is_favicon() || $is_IIS && !iis7_supports_permalinks()) {
        return;
    }
    if (!$requested_url && isset($_SERVER['HTTP_HOST'])) {
        // Build the URL in the address bar.
        $requested_url = is_ssl() ? 'https://' : 'http://';
        $requested_url .= $_SERVER['HTTP_HOST'];
        $requested_url .= $_SERVER['REQUEST_URI'];
    }
    $original = parse_url($requested_url);
    if (false === $original) {
        return;
    }
    $redirect = $original;
    $redirect_url = false;
    // Notice fixing.
    if (!isset($redirect['path'])) {
        $redirect['path'] = '';
    }
    if (!isset($redirect['query'])) {
        $redirect['query'] = '';
    }
    /*
     * If the original URL ended with non-breaking spaces, they were almost
     * certainly inserted by accident. Let's remove them, so the reader doesn't
     * see a 404 error with no obvious cause.
     */
    $redirect['path'] = preg_replace('|(%C2%A0)+$|i', '', $redirect['path']);
    // It's not a preview, so remove it from URL.
    if (get_query_var('preview')) {
        $redirect['query'] = remove_query_arg('preview', $redirect['query']);
    }
    $post_id = get_query_var('p');
    if (is_feed() && $post_id) {
        $redirect_url = get_post_comments_feed_link($post_id, get_query_var('feed'));
        if ($redirect_url) {
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type', 'feed'), $redirect_url);
            $redirect['path'] = parse_url($redirect_url, PHP_URL_PATH);
        }
    }
    if (is_singular() && $wp_query->post_count < 1 && $post_id) {
        $vars = $wpdb->get_results($wpdb->prepare("SELECT post_type, post_parent FROM {$wpdb->posts} WHERE ID = %d", $post_id));
        if (!empty($vars[0])) {
            $vars = $vars[0];
            if ('revision' === $vars->post_type && $vars->post_parent > 0) {
                $post_id = $vars->post_parent;
            }
            $redirect_url = get_permalink($post_id);
            if ($redirect_url) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    }
    // These tests give us a WP-generated permalink.
    if (is_404()) {
        // Redirect ?page_id, ?p=, ?attachment_id= to their respective URLs.
        $post_id = max(get_query_var('p'), get_query_var('page_id'), get_query_var('attachment_id'));
        $redirect_post = $post_id ? get_post($post_id) : false;
        if ($redirect_post) {
            $post_type_obj = get_post_type_object($redirect_post->post_type);
            if ($post_type_obj->public && 'auto-draft' !== $redirect_post->post_status) {
                $redirect_url = get_permalink($redirect_post);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
        $year = get_query_var('year');
        $month = get_query_var('monthnum');
        $day = get_query_var('day');
        if ($year && $month && $day) {
            $date = sprintf('%04d-%02d-%02d', $year, $month, $day);
            if (!wp_checkdate($month, $day, $year, $date)) {
                $redirect_url = get_month_link($year, $month);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum', 'day'), $redirect_url);
            }
        } elseif ($year && $month && $month > 12) {
            $redirect_url = get_year_link($year);
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum'), $redirect_url);
        }
        // Strip off non-existing <!--nextpage--> links from single posts or pages.
        if (get_query_var('page')) {
            $post_id = 0;
            if ($wp_query->queried_object instanceof WP_Post) {
                $post_id = $wp_query->queried_object->ID;
            } elseif ($wp_query->post) {
                $post_id = $wp_query->post->ID;
            }
            if ($post_id) {
                $redirect_url = get_permalink($post_id);
                $redirect['path'] = rtrim($redirect['path'], (int) get_query_var('page') . '/');
                $redirect['query'] = remove_query_arg('page', $redirect['query']);
            }
        }
        if (!$redirect_url) {
            $redirect_url = redirect_guess_404_permalink();
            if ($redirect_url) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('page', 'feed', 'p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    } elseif (is_object($wp_rewrite) && $wp_rewrite->using_permalinks()) {
        // Rewriting of old ?p=X, ?m=2004, ?m=200401, ?m=20040101.
        if (is_attachment() && !array_diff(array_keys($wp->query_vars), array('attachment', 'attachment_id')) && !$redirect_url) {
            if (!empty($_GET['attachment_id'])) {
                $redirect_url = get_attachment_link(get_query_var('attachment_id'));
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('attachment_id', $redirect['query']);
                }
            } else {
                $redirect_url = get_attachment_link();
            }
        } elseif (is_single() && !empty($_GET['p']) && !$redirect_url) {
            $redirect_url = get_permalink(get_query_var('p'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg(array('p', 'post_type'), $redirect['query']);
            }
        } elseif (is_single() && !empty($_GET['name']) && !$redirect_url) {
            $redirect_url = get_permalink($wp_query->get_queried_object_id());
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('name', $redirect['query']);
            }
        } elseif (is_page() && !empty($_GET['page_id']) && !$redirect_url) {
            $redirect_url = get_permalink(get_query_var('page_id'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (is_page() && !is_feed() && !$redirect_url && 'page' === get_option('show_on_front') && get_queried_object_id() === (int) get_option('page_on_front')) {
            $redirect_url = home_url('/');
        } elseif (is_home() && !empty($_GET['page_id']) && !$redirect_url && 'page' === get_option('show_on_front') && get_query_var('page_id') === (int) get_option('page_for_posts')) {
            $redirect_url = get_permalink(get_option('page_for_posts'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (!empty($_GET['m']) && (is_year() || is_month() || is_day())) {
            $m = get_query_var('m');
            switch (strlen($m)) {
                case 4:
                    // Yearly.
                    $redirect_url = get_year_link($m);
                    break;
                case 6:
                    // Monthly.
                    $redirect_url = get_month_link(substr($m, 0, 4), substr($m, 4, 2));
                    break;
                case 8:
                    // Daily.
                    $redirect_url = get_day_link(substr($m, 0, 4), substr($m, 4, 2), substr($m, 6, 2));
                    break;
            }
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('m', $redirect['query']);
            }
            // Now moving on to non ?m=X year/month/day links.
        } elseif (is_date()) {
            $year = get_query_var('year');
            $month = get_query_var('monthnum');
            $day = get_query_var('day');
            if (is_day() && $year && $month && !empty($_GET['day'])) {
                $redirect_url = get_day_link($year, $month, $day);
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg(array('year', 'monthnum', 'day'), $redirect['query']);
                }
            } elseif (is_month() && $year && !empty($_GET['monthnum'])) {
                $redirect_url = get_month_link($year, $month);
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg(array('year', 'monthnum'), $redirect['query']);
                }
            } elseif (is_year() && !empty($_GET['year'])) {
                $redirect_url = get_year_link($year);
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('year', $redirect['query']);
                }
            }
        } elseif (is_author() && !empty($_GET['author']) && preg_match('|^[0-9]+$|', $_GET['author'])) {
            $author = get_userdata(get_query_var('author'));
            if (false !== $author && $wpdb->get_var($wpdb->prepare("SELECT ID FROM {$wpdb->posts} WHERE {$wpdb->posts}.post_author = %d AND {$wpdb->posts}.post_status = 'publish' LIMIT 1", $author->ID))) {
                $redirect_url = get_author_posts_url($author->ID, $author->user_nicename);
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('author', $redirect['query']);
                }
            }
        } elseif (is_category() || is_tag() || is_tax()) {
            // Terms (tags/categories).
            $term_count = 0;
            foreach ($wp_query->tax_query->queried_terms as $tax_query) {
                $term_count += count($tax_query['terms']);
            }
            $obj = $wp_query->get_queried_object();
            if ($term_count <= 1 && !empty($obj->term_id)) {
                $tax_url = get_term_link((int) $obj->term_id, $obj->taxonomy);
                if ($tax_url && !is_wp_error($tax_url)) {
                    if (!empty($redirect['query'])) {
                        // Strip taxonomy query vars off the URL.
                        $qv_remove = array('term', 'taxonomy');
                        if (is_category()) {
                            $qv_remove[] = 'category_name';
                            $qv_remove[] = 'cat';
                        } elseif (is_tag()) {
                            $qv_remove[] = 'tag';
                            $qv_remove[] = 'tag_id';
                        } else {
                            // Custom taxonomies will have a custom query var, remove those too.
                            $tax_obj = get_taxonomy($obj->taxonomy);
                            if (false !== $tax_obj->query_var) {
                                $qv_remove[] = $tax_obj->query_var;
                            }
                        }
                        $rewrite_vars = array_diff(array_keys($wp_query->query), array_keys($_GET));
                        // Check to see if all the query vars are coming from the rewrite, none are set via $_GET.
                        if (!array_diff($rewrite_vars, array_keys($_GET))) {
                            // Remove all of the per-tax query vars.
                            $redirect['query'] = remove_query_arg($qv_remove, $redirect['query']);
                            // Create the destination URL for this taxonomy.
                            $tax_url = parse_url($tax_url);
                            if (!empty($tax_url['query'])) {
                                // Taxonomy accessible via ?taxonomy=...&term=... or any custom query var.
                                parse_str($tax_url['query'], $query_vars);
                                $redirect['query'] = add_query_arg($query_vars, $redirect['query']);
                            } else {
                                // Taxonomy is accessible via a "pretty URL".
                                $redirect['path'] = $tax_url['path'];
                            }
                        } else {
                            // Some query vars are set via $_GET. Unset those from $_GET that exist via the rewrite.
                            foreach ($qv_remove as $_qv) {
                                if (isset($rewrite_vars[$_qv])) {
                                    $redirect['query'] = remove_query_arg($_qv, $redirect['query']);
                                }
                            }
                        }
                    }
                }
            }
        } elseif (is_single() && strpos($wp_rewrite->permalink_structure, '%category%') !== false) {
            $category_name = get_query_var('category_name');
            if ($category_name) {
                $category = get_category_by_path($category_name);
                if (!$category || is_wp_error($category) || !has_term($category->term_id, 'category', $wp_query->get_queried_object_id())) {
                    $redirect_url = get_permalink($wp_query->get_queried_object_id());
                }
            }
        }
        // Post paging.
        if (is_singular() && get_query_var('page')) {
            $page = get_query_var('page');
            if (!$redirect_url) {
                $redirect_url = get_permalink(get_queried_object_id());
            }
            if ($page > 1) {
                $redirect_url = trailingslashit($redirect_url);
                if (is_front_page()) {
                    $redirect_url .= user_trailingslashit("{$wp_rewrite->pagination_base}/{$page}", 'paged');
                } else {
                    $redirect_url .= user_trailingslashit($page, 'single_paged');
                }
            }
            $redirect['query'] = remove_query_arg('page', $redirect['query']);
        }
        if (get_query_var('sitemap')) {
            $redirect_url = get_sitemap_url(get_query_var('sitemap'), get_query_var('sitemap-subtype'), get_query_var('paged'));
            $redirect['query'] = remove_query_arg(array('sitemap', 'sitemap-subtype', 'paged'), $redirect['query']);
        } elseif (get_query_var('paged') || is_feed() || get_query_var('cpage')) {
            // Paging and feeds.
            $paged = get_query_var('paged');
            $feed = get_query_var('feed');
            $cpage = get_query_var('cpage');
            while (preg_match("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", $redirect['path']) || preg_match('#/(comments/?)?(feed|rss2?|rdf|atom)(/+)?$#', $redirect['path']) || preg_match("#/{$wp_rewrite->comments_pagination_base}-[0-9]+(/+)?\$#", $redirect['path'])) {
                // Strip off any existing paging.
                $redirect['path'] = preg_replace("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", '/', $redirect['path']);
                // Strip off feed endings.
                $redirect['path'] = preg_replace('#/(comments/?)?(feed|rss2?|rdf|atom)(/+|$)#', '/', $redirect['path']);
                // Strip off any existing comment paging.
                $redirect['path'] = preg_replace("#/{$wp_rewrite->comments_pagination_base}-[0-9]+?(/+)?\$#", '/', $redirect['path']);
            }
            $addl_path = '';
            $default_feed = get_default_feed();
            if (is_feed() && in_array($feed, $wp_rewrite->feeds, true)) {
                $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                if (!is_singular() && get_query_var('withcomments')) {
                    $addl_path .= 'comments/';
                }
                if ('rss' === $default_feed && 'feed' === $feed || 'rss' === $feed) {
                    $format = ('rss2' === $default_feed) ? '' : 'rss2';
                } else {
                    $format = ($default_feed === $feed || 'feed' === $feed) ? '' : $feed;
                }
                $addl_path .= user_trailingslashit('feed/' . $format, 'feed');
                $redirect['query'] = remove_query_arg('feed', $redirect['query']);
            } elseif (is_feed() && 'old' === $feed) {
                $old_feed_files = array('wp-atom.php' => 'atom', 'wp-commentsrss2.php' => 'comments_rss2', 'wp-feed.php' => $default_feed, 'wp-rdf.php' => 'rdf', 'wp-rss.php' => 'rss2', 'wp-rss2.php' => 'rss2');
                if (isset($old_feed_files[basename($redirect['path'])])) {
                    $redirect_url = get_feed_link($old_feed_files[basename($redirect['path'])]);
                    wp_redirect($redirect_url, 301);
                    die;
                }
            }
            if ($paged > 0) {
                $redirect['query'] = remove_query_arg('paged', $redirect['query']);
                if (!is_feed()) {
                    if (!is_single()) {
                        $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                        if ($paged > 1) {
                            $addl_path .= user_trailingslashit("{$wp_rewrite->pagination_base}/{$paged}", 'paged');
                        }
                    }
                } elseif ($paged > 1) {
                    $redirect['query'] = add_query_arg('paged', $paged, $redirect['query']);
                }
            }
            $default_comments_page = get_option('default_comments_page');
            if (get_option('page_comments') && ('newest' === $default_comments_page && $cpage > 0 || 'newest' !== $default_comments_page && $cpage > 1)) {
                $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                $addl_path .= user_trailingslashit($wp_rewrite->comments_pagination_base . '-' . $cpage, 'commentpaged');
                $redirect['query'] = remove_query_arg('cpage', $redirect['query']);
            }
            // Strip off trailing /index.php/.
            $redirect['path'] = preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/?$|', '/', $redirect['path']);
            $redirect['path'] = user_trailingslashit($redirect['path']);
            if (!empty($addl_path) && $wp_rewrite->using_index_permalinks() && strpos($redirect['path'], '/' . $wp_rewrite->index . '/') === false) {
                $redirect['path'] = trailingslashit($redirect['path']) . $wp_rewrite->index . '/';
            }
            if (!empty($addl_path)) {
                $redirect['path'] = trailingslashit($redirect['path']) . $addl_path;
            }
            $redirect_url = $redirect['scheme'] . '://' . $redirect['host'] . $redirect['path'];
        }
        if ('wp-register.php' === basename($redirect['path'])) {
            if (is_multisite()) {
                /** This filter is documented in wp-login.php */
                $redirect_url = apply_filters('wp_signup_location', network_site_url('wp-signup.php'));
            } else {
                $redirect_url = wp_registration_url();
            }
            wp_redirect($redirect_url, 301);
            die;
        }
    }
    $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    // Tack on any additional query vars.
    if ($redirect_url && !empty($redirect['query'])) {
        parse_str($redirect['query'], $_parsed_query);
        $redirect = parse_url($redirect_url);
        if (!empty($_parsed_query['name']) && !empty($redirect['query'])) {
            parse_str($redirect['query'], $_parsed_redirect_query);
            if (empty($_parsed_redirect_query['name'])) {
                unset($_parsed_query['name']);
            }
        }
        $_parsed_query = array_combine(rawurlencode_deep(array_keys($_parsed_query)), rawurlencode_deep(array_values($_parsed_query)));
        $redirect_url = add_query_arg($_parsed_query, $redirect_url);
    }
    if ($redirect_url) {
        $redirect = parse_url($redirect_url);
    }
    // www.example.com vs. example.com
    $user_home = parse_url(home_url());
    if (!empty($user_home['host'])) {
        $redirect['host'] = $user_home['host'];
    }
    if (empty($user_home['path'])) {
        $user_home['path'] = '/';
    }
    // Handle ports.
    if (!empty($user_home['port'])) {
        $redirect['port'] = $user_home['port'];
    } else {
        unset($redirect['port']);
    }
    // Trailing /index.php.
    $redirect['path'] = preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/*?$|', '/', $redirect['path']);
    $punctuation_pattern = implode('|', array_map('preg_quote', array(
        ' ',
        '%20',
        // Space.
        '!',
        '%21',
        // Exclamation mark.
        '"',
        '%22',
        // Double quote.
        "'",
        '%27',
        // Single quote.
        '(',
        '%28',
        // Opening bracket.
        ')',
        '%29',
        // Closing bracket.
        ',',
        '%2C',
        // Comma.
        '.',
        '%2E',
        // Period.
        ';',
        '%3B',
        // Semicolon.
        '{',
        '%7B',
        // Opening curly bracket.
        '}',
        '%7D',
        // Closing curly bracket.
        '%E2%80%9C',
        // Opening curly quote.
        '%E2%80%9D',
    )));
    // Remove trailing spaces and end punctuation from the path.
    $redirect['path'] = preg_replace("#({$punctuation_pattern})+\$#", '', $redirect['path']);
    if (!empty($redirect['query'])) {
        // Remove trailing spaces and end punctuation from certain terminating query string args.
        $redirect['query'] = preg_replace("#((^|&)(p|page_id|cat|tag)=[^&]*?)({$punctuation_pattern})+\$#", '$1', $redirect['query']);
        // Clean up empty query strings.
        $redirect['query'] = trim(preg_replace('#(^|&)(p|page_id|cat|tag)=?(&|$)#', '&', $redirect['query']), '&');
        // Redirect obsolete feeds.
        $redirect['query'] = preg_replace('#(^|&)feed=rss(&|$)#', '$1feed=rss2$2', $redirect['query']);
        // Remove redundant leading ampersands.
        $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    }
    // Strip /index.php/ when we're not using PATHINFO permalinks.
    if (!$wp_rewrite->using_index_permalinks()) {
        $redirect['path'] = str_replace('/' . $wp_rewrite->index . '/', '/', $redirect['path']);
    }
    // Trailing slashes.
    if (is_object($wp_rewrite) && $wp_rewrite->using_permalinks() && !is_404() && (!is_front_page() || is_front_page() && get_query_var('paged') > 1)) {
        $user_ts_type = '';
        if (get_query_var('paged') > 0) {
            $user_ts_type = 'paged';
        } else {
            foreach (array('single', 'category', 'page', 'day', 'month', 'year', 'home') as $type) {
                $func = 'is_' . $type;
                if (call_user_func($func)) {
                    $user_ts_type = $type;
                    break;
                }
            }
        }
        $redirect['path'] = user_trailingslashit($redirect['path'], $user_ts_type);
    } elseif (is_front_page()) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Remove trailing slash for robots.txt or sitemap requests.
    if (is_robots() || !empty(get_query_var('sitemap')) || !empty(get_query_var('sitemap-stylesheet'))) {
        $redirect['path'] = untrailingslashit($redirect['path']);
    }
    // Strip multiple slashes out of the URL.
    if (strpos($redirect['path'], '//') > -1) {
        $redirect['path'] = preg_replace('|/+|', '/', $redirect['path']);
    }
    // Always trailing slash the Front Page URL.
    if (trailingslashit($redirect['path']) === trailingslashit($user_home['path'])) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    $original_host_low = strtolower($original['host']);
    $redirect_host_low = strtolower($redirect['host']);
    // Ignore differences in host capitalization, as this can lead to infinite redirects.
    // Only redirect no-www <=> yes-www.
    if ($original_host_low === $redirect_host_low || 'www.' . $original_host_low !== $redirect_host_low && 'www.' . $redirect_host_low !== $original_host_low) {
        $redirect['host'] = $original['host'];
    }
    $compare_original = array($original['host'], $original['path']);
    if (!empty($original['port'])) {
        $compare_original[] = $original['port'];
    }
    if (!empty($original['query'])) {
        $compare_original[] = $original['query'];
    }
    $compare_redirect = array($redirect['host'], $redirect['path']);
    if (!empty($redirect['port'])) {
        $compare_redirect[] = $redirect['port'];
    }
    if (!empty($redirect['query'])) {
        $compare_redirect[] = $redirect['query'];
    }
    if ($compare_original !== $compare_redirect) {
        $redirect_url = $redirect['scheme'] . '://' . $redirect['host'];
        if (!empty($redirect['port'])) {
            $redirect_url .= ':' . $redirect['port'];
        }
        $redirect_url .= $redirect['path'];
        if (!empty($redirect['query'])) {
            $redirect_url .= '?' . $redirect['query'];
        }
    }
    if (!$redirect_url || $redirect_url === $requested_url) {
        return;
    }
    // Hex encoded octets are case-insensitive.
    if (false !== strpos($requested_url, '%')) {
        if (!function_exists('lowercase_octets')) {
            /**
             * Converts the first hex-encoded octet match to lowercase.
             *
             * @since 3.1.0
             * @ignore
             *
             * @param array $matches Hex-encoded octet matches for the requested URL.
             * @return string Lowercased version of the first match.
             */
            function lowercase_octets($matches)
            {
                return strtolower($matches[0]);
            }
        }
        $requested_url = preg_replace_callback('|%[a-fA-F0-9][a-fA-F0-9]|', 'lowercase_octets', $requested_url);
    }
    /**
     * Filters the canonical redirect URL.
     *
     * Returning false to this filter will cancel the redirect.
     *
     * @since 2.3.0
     *
     * @param string $redirect_url  The redirect URL.
     * @param string $requested_url The requested URL.
     */
    $redirect_url = apply_filters('redirect_canonical', $redirect_url, $requested_url);
    // Yes, again -- in case the filter aborted the request.
    if (!$redirect_url || strip_fragment_from_url($redirect_url) === strip_fragment_from_url($requested_url)) {
        return;
    }
    if ($do_redirect) {
        // Protect against chained redirects.
        if (!redirect_canonical($redirect_url, false)) {
            wp_redirect($redirect_url, 301);
            exit;
        } else {
            // Debug.
            // die("1: $redirect_url<br />2: " . redirect_canonical( $redirect_url, false ) );
            return;
        }
    } else {
        return $redirect_url;
    }
}

WordPress Version: 5.5

/**
 * Canonical API to handle WordPress Redirecting
 *
 * Based on "Permalink Redirect" from Scott Yang and "Enforce www. Preference"
 * by Mark Jaquith
 *
 * @package WordPress
 * @since 2.3.0
 */
/**
 * Redirects incoming links to the proper URL based on the site url.
 *
 * Search engines consider www.somedomain.com and somedomain.com to be two
 * different URLs when they both go to the same location. This SEO enhancement
 * prevents penalty for duplicate content by redirecting all incoming links to
 * one or the other.
 *
 * Prevents redirection for feeds, trackbacks, searches, and
 * admin URLs. Does not redirect on non-pretty-permalink-supporting IIS 7+,
 * page/post previews, WP admin, Trackbacks, robots.txt, favicon.ico, searches,
 * or on POST requests.
 *
 * Will also attempt to find the correct link when a user enters a URL that does
 * not exist based on exact WordPress query. Will instead try to parse the URL
 * or query in an attempt to figure the correct page to go to.
 *
 * @since 2.3.0
 *
 * @global WP_Rewrite $wp_rewrite WordPress rewrite component.
 * @global bool       $is_IIS
 * @global WP_Query   $wp_query   WordPress Query object.
 * @global wpdb       $wpdb       WordPress database abstraction object.
 * @global WP         $wp         Current WordPress environment instance.
 *
 * @param string $requested_url Optional. The URL that was requested, used to
 *                              figure if redirect is needed.
 * @param bool   $do_redirect   Optional. Redirect to the new URL.
 * @return string|void The string of the URL, if redirect needed.
 */
function redirect_canonical($requested_url = null, $do_redirect = true)
{
    global $wp_rewrite, $is_IIS, $wp_query, $wpdb, $wp;
    if (isset($_SERVER['REQUEST_METHOD']) && !in_array(strtoupper($_SERVER['REQUEST_METHOD']), array('GET', 'HEAD'), true)) {
        return;
    }
    // If we're not in wp-admin and the post has been published and preview nonce
    // is non-existent or invalid then no need for preview in query.
    if (is_preview() && get_query_var('p') && 'publish' === get_post_status(get_query_var('p'))) {
        if (!isset($_GET['preview_id']) || !isset($_GET['preview_nonce']) || !wp_verify_nonce($_GET['preview_nonce'], 'post_preview_' . (int) $_GET['preview_id'])) {
            $wp_query->is_preview = false;
        }
    }
    if (is_admin() || is_search() || is_preview() || is_trackback() || is_favicon() || $is_IIS && !iis7_supports_permalinks()) {
        return;
    }
    if (!$requested_url && isset($_SERVER['HTTP_HOST'])) {
        // Build the URL in the address bar.
        $requested_url = is_ssl() ? 'https://' : 'http://';
        $requested_url .= $_SERVER['HTTP_HOST'];
        $requested_url .= $_SERVER['REQUEST_URI'];
    }
    $original = parse_url($requested_url);
    if (false === $original) {
        return;
    }
    $redirect = $original;
    $redirect_url = false;
    // Notice fixing.
    if (!isset($redirect['path'])) {
        $redirect['path'] = '';
    }
    if (!isset($redirect['query'])) {
        $redirect['query'] = '';
    }
    /*
     * If the original URL ended with non-breaking spaces, they were almost
     * certainly inserted by accident. Let's remove them, so the reader doesn't
     * see a 404 error with no obvious cause.
     */
    $redirect['path'] = preg_replace('|(%C2%A0)+$|i', '', $redirect['path']);
    // It's not a preview, so remove it from URL.
    if (get_query_var('preview')) {
        $redirect['query'] = remove_query_arg('preview', $redirect['query']);
    }
    $post_id = get_query_var('p');
    if (is_feed() && $post_id) {
        $redirect_url = get_post_comments_feed_link($post_id, get_query_var('feed'));
        if ($redirect_url) {
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type', 'feed'), $redirect_url);
            $redirect['path'] = parse_url($redirect_url, PHP_URL_PATH);
        }
    }
    if (is_singular() && $wp_query->post_count < 1 && $post_id) {
        $vars = $wpdb->get_results($wpdb->prepare("SELECT post_type, post_parent FROM {$wpdb->posts} WHERE ID = %d", $post_id));
        if (!empty($vars[0])) {
            $vars = $vars[0];
            if ('revision' === $vars->post_type && $vars->post_parent > 0) {
                $post_id = $vars->post_parent;
            }
            $redirect_url = get_permalink($post_id);
            if ($redirect_url) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    }
    // These tests give us a WP-generated permalink.
    if (is_404()) {
        // Redirect ?page_id, ?p=, ?attachment_id= to their respective URLs.
        $post_id = max(get_query_var('p'), get_query_var('page_id'), get_query_var('attachment_id'));
        $redirect_post = $post_id ? get_post($post_id) : false;
        if ($redirect_post) {
            $post_type_obj = get_post_type_object($redirect_post->post_type);
            if ($post_type_obj->public && 'auto-draft' !== $redirect_post->post_status) {
                $redirect_url = get_permalink($redirect_post);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
        $year = get_query_var('year');
        $month = get_query_var('monthnum');
        $day = get_query_var('day');
        if ($year && $month && $day) {
            $date = sprintf('%04d-%02d-%02d', $year, $month, $day);
            if (!wp_checkdate($month, $day, $year, $date)) {
                $redirect_url = get_month_link($year, $month);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum', 'day'), $redirect_url);
            }
        } elseif ($year && $month && $month > 12) {
            $redirect_url = get_year_link($year);
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum'), $redirect_url);
        }
        // Strip off non-existing <!--nextpage--> links from single posts or pages.
        if (get_query_var('page')) {
            $post_id = 0;
            if ($wp_query->queried_object instanceof WP_Post) {
                $post_id = $wp_query->queried_object->ID;
            } elseif ($wp_query->post) {
                $post_id = $wp_query->post->ID;
            }
            if ($post_id) {
                $redirect_url = get_permalink($post_id);
                $redirect['path'] = rtrim($redirect['path'], (int) get_query_var('page') . '/');
                $redirect['query'] = remove_query_arg('page', $redirect['query']);
            }
        }
        if (!$redirect_url) {
            $redirect_url = redirect_guess_404_permalink();
            if ($redirect_url) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('page', 'feed', 'p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    } elseif (is_object($wp_rewrite) && $wp_rewrite->using_permalinks()) {
        // Rewriting of old ?p=X, ?m=2004, ?m=200401, ?m=20040101.
        if (is_attachment() && !array_diff(array_keys($wp->query_vars), array('attachment', 'attachment_id')) && !$redirect_url) {
            if (!empty($_GET['attachment_id'])) {
                $redirect_url = get_attachment_link(get_query_var('attachment_id'));
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('attachment_id', $redirect['query']);
                }
            } else {
                $redirect_url = get_attachment_link();
            }
        } elseif (is_single() && !empty($_GET['p']) && !$redirect_url) {
            $redirect_url = get_permalink(get_query_var('p'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg(array('p', 'post_type'), $redirect['query']);
            }
        } elseif (is_single() && !empty($_GET['name']) && !$redirect_url) {
            $redirect_url = get_permalink($wp_query->get_queried_object_id());
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('name', $redirect['query']);
            }
        } elseif (is_page() && !empty($_GET['page_id']) && !$redirect_url) {
            $redirect_url = get_permalink(get_query_var('page_id'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (is_page() && !is_feed() && !$redirect_url && 'page' === get_option('show_on_front') && get_queried_object_id() === (int) get_option('page_on_front')) {
            $redirect_url = home_url('/');
        } elseif (is_home() && !empty($_GET['page_id']) && !$redirect_url && 'page' === get_option('show_on_front') && get_query_var('page_id') === (int) get_option('page_for_posts')) {
            $redirect_url = get_permalink(get_option('page_for_posts'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (!empty($_GET['m']) && (is_year() || is_month() || is_day())) {
            $m = get_query_var('m');
            switch (strlen($m)) {
                case 4:
                    // Yearly.
                    $redirect_url = get_year_link($m);
                    break;
                case 6:
                    // Monthly.
                    $redirect_url = get_month_link(substr($m, 0, 4), substr($m, 4, 2));
                    break;
                case 8:
                    // Daily.
                    $redirect_url = get_day_link(substr($m, 0, 4), substr($m, 4, 2), substr($m, 6, 2));
                    break;
            }
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('m', $redirect['query']);
            }
            // Now moving on to non ?m=X year/month/day links.
        } elseif (is_date()) {
            $year = get_query_var('year');
            $month = get_query_var('monthnum');
            $day = get_query_var('day');
            if (is_day() && $year && $month && !empty($_GET['day'])) {
                $redirect_url = get_day_link($year, $month, $day);
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg(array('year', 'monthnum', 'day'), $redirect['query']);
                }
            } elseif (is_month() && $year && !empty($_GET['monthnum'])) {
                $redirect_url = get_month_link($year, $month);
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg(array('year', 'monthnum'), $redirect['query']);
                }
            } elseif (is_year() && !empty($_GET['year'])) {
                $redirect_url = get_year_link($year);
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('year', $redirect['query']);
                }
            }
        } elseif (is_author() && !empty($_GET['author']) && preg_match('|^[0-9]+$|', $_GET['author'])) {
            $author = get_userdata(get_query_var('author'));
            if (false !== $author && $wpdb->get_var($wpdb->prepare("SELECT ID FROM {$wpdb->posts} WHERE {$wpdb->posts}.post_author = %d AND {$wpdb->posts}.post_status = 'publish' LIMIT 1", $author->ID))) {
                $redirect_url = get_author_posts_url($author->ID, $author->user_nicename);
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('author', $redirect['query']);
                }
            }
        } elseif (is_category() || is_tag() || is_tax()) {
            // Terms (tags/categories).
            $term_count = 0;
            foreach ($wp_query->tax_query->queried_terms as $tax_query) {
                $term_count += count($tax_query['terms']);
            }
            $obj = $wp_query->get_queried_object();
            if ($term_count <= 1 && !empty($obj->term_id)) {
                $tax_url = get_term_link((int) $obj->term_id, $obj->taxonomy);
                if ($tax_url && !is_wp_error($tax_url)) {
                    if (!empty($redirect['query'])) {
                        // Strip taxonomy query vars off the URL.
                        $qv_remove = array('term', 'taxonomy');
                        if (is_category()) {
                            $qv_remove[] = 'category_name';
                            $qv_remove[] = 'cat';
                        } elseif (is_tag()) {
                            $qv_remove[] = 'tag';
                            $qv_remove[] = 'tag_id';
                        } else {
                            // Custom taxonomies will have a custom query var, remove those too.
                            $tax_obj = get_taxonomy($obj->taxonomy);
                            if (false !== $tax_obj->query_var) {
                                $qv_remove[] = $tax_obj->query_var;
                            }
                        }
                        $rewrite_vars = array_diff(array_keys($wp_query->query), array_keys($_GET));
                        // Check to see if all the query vars are coming from the rewrite, none are set via $_GET.
                        if (!array_diff($rewrite_vars, array_keys($_GET))) {
                            // Remove all of the per-tax query vars.
                            $redirect['query'] = remove_query_arg($qv_remove, $redirect['query']);
                            // Create the destination URL for this taxonomy.
                            $tax_url = parse_url($tax_url);
                            if (!empty($tax_url['query'])) {
                                // Taxonomy accessible via ?taxonomy=...&term=... or any custom query var.
                                parse_str($tax_url['query'], $query_vars);
                                $redirect['query'] = add_query_arg($query_vars, $redirect['query']);
                            } else {
                                // Taxonomy is accessible via a "pretty URL".
                                $redirect['path'] = $tax_url['path'];
                            }
                        } else {
                            // Some query vars are set via $_GET. Unset those from $_GET that exist via the rewrite.
                            foreach ($qv_remove as $_qv) {
                                if (isset($rewrite_vars[$_qv])) {
                                    $redirect['query'] = remove_query_arg($_qv, $redirect['query']);
                                }
                            }
                        }
                    }
                }
            }
        } elseif (is_single() && strpos($wp_rewrite->permalink_structure, '%category%') !== false) {
            $category_name = get_query_var('category_name');
            if ($category_name) {
                $category = get_category_by_path($category_name);
                if (!$category || is_wp_error($category) || !has_term($category->term_id, 'category', $wp_query->get_queried_object_id())) {
                    $redirect_url = get_permalink($wp_query->get_queried_object_id());
                }
            }
        }
        // Post paging.
        if (is_singular() && get_query_var('page')) {
            $page = get_query_var('page');
            if (!$redirect_url) {
                $redirect_url = get_permalink(get_queried_object_id());
            }
            if ($page > 1) {
                $redirect_url = trailingslashit($redirect_url);
                if (is_front_page()) {
                    $redirect_url .= user_trailingslashit("{$wp_rewrite->pagination_base}/{$page}", 'paged');
                } else {
                    $redirect_url .= user_trailingslashit($page, 'single_paged');
                }
            }
            $redirect['query'] = remove_query_arg('page', $redirect['query']);
        }
        // Paging and feeds.
        if (get_query_var('paged') || is_feed() || get_query_var('cpage')) {
            $paged = get_query_var('paged');
            $feed = get_query_var('feed');
            $cpage = get_query_var('cpage');
            while (preg_match("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", $redirect['path']) || preg_match('#/(comments/?)?(feed|rss2?|rdf|atom)(/+)?$#', $redirect['path']) || preg_match("#/{$wp_rewrite->comments_pagination_base}-[0-9]+(/+)?\$#", $redirect['path'])) {
                // Strip off any existing paging.
                $redirect['path'] = preg_replace("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", '/', $redirect['path']);
                // Strip off feed endings.
                $redirect['path'] = preg_replace('#/(comments/?)?(feed|rss2?|rdf|atom)(/+|$)#', '/', $redirect['path']);
                // Strip off any existing comment paging.
                $redirect['path'] = preg_replace("#/{$wp_rewrite->comments_pagination_base}-[0-9]+?(/+)?\$#", '/', $redirect['path']);
            }
            $addl_path = '';
            $default_feed = get_default_feed();
            if (is_feed() && in_array($feed, $wp_rewrite->feeds, true)) {
                $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                if (!is_singular() && get_query_var('withcomments')) {
                    $addl_path .= 'comments/';
                }
                if ('rss' === $default_feed && 'feed' === $feed || 'rss' === $feed) {
                    $format = ('rss2' === $default_feed) ? '' : 'rss2';
                } else {
                    $format = ($default_feed === $feed || 'feed' === $feed) ? '' : $feed;
                }
                $addl_path .= user_trailingslashit('feed/' . $format, 'feed');
                $redirect['query'] = remove_query_arg('feed', $redirect['query']);
            } elseif (is_feed() && 'old' === $feed) {
                $old_feed_files = array('wp-atom.php' => 'atom', 'wp-commentsrss2.php' => 'comments_rss2', 'wp-feed.php' => $default_feed, 'wp-rdf.php' => 'rdf', 'wp-rss.php' => 'rss2', 'wp-rss2.php' => 'rss2');
                if (isset($old_feed_files[basename($redirect['path'])])) {
                    $redirect_url = get_feed_link($old_feed_files[basename($redirect['path'])]);
                    wp_redirect($redirect_url, 301);
                    die;
                }
            }
            if ($paged > 0) {
                $redirect['query'] = remove_query_arg('paged', $redirect['query']);
                if (!is_feed()) {
                    if (!is_single()) {
                        $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                        if ($paged > 1) {
                            $addl_path .= user_trailingslashit("{$wp_rewrite->pagination_base}/{$paged}", 'paged');
                        }
                    }
                } elseif ($paged > 1) {
                    $redirect['query'] = add_query_arg('paged', $paged, $redirect['query']);
                }
            }
            $default_comments_page = get_option('default_comments_page');
            if (get_option('page_comments') && ('newest' === $default_comments_page && $cpage > 0 || 'newest' !== $default_comments_page && $cpage > 1)) {
                $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                $addl_path .= user_trailingslashit($wp_rewrite->comments_pagination_base . '-' . $cpage, 'commentpaged');
                $redirect['query'] = remove_query_arg('cpage', $redirect['query']);
            }
            // Strip off trailing /index.php/.
            $redirect['path'] = preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/?$|', '/', $redirect['path']);
            $redirect['path'] = user_trailingslashit($redirect['path']);
            if (!empty($addl_path) && $wp_rewrite->using_index_permalinks() && strpos($redirect['path'], '/' . $wp_rewrite->index . '/') === false) {
                $redirect['path'] = trailingslashit($redirect['path']) . $wp_rewrite->index . '/';
            }
            if (!empty($addl_path)) {
                $redirect['path'] = trailingslashit($redirect['path']) . $addl_path;
            }
            // Remove trailing slash for sitemaps requests.
            if (!empty(get_query_var('sitemap'))) {
                $redirect['path'] = untrailingslashit($redirect['path']);
            }
            $redirect_url = $redirect['scheme'] . '://' . $redirect['host'] . $redirect['path'];
        }
        if ('wp-register.php' === basename($redirect['path'])) {
            if (is_multisite()) {
                /** This filter is documented in wp-login.php */
                $redirect_url = apply_filters('wp_signup_location', network_site_url('wp-signup.php'));
            } else {
                $redirect_url = wp_registration_url();
            }
            wp_redirect($redirect_url, 301);
            die;
        }
    }
    $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    // Tack on any additional query vars.
    if ($redirect_url && !empty($redirect['query'])) {
        parse_str($redirect['query'], $_parsed_query);
        $redirect = parse_url($redirect_url);
        if (!empty($_parsed_query['name']) && !empty($redirect['query'])) {
            parse_str($redirect['query'], $_parsed_redirect_query);
            if (empty($_parsed_redirect_query['name'])) {
                unset($_parsed_query['name']);
            }
        }
        $_parsed_query = array_combine(rawurlencode_deep(array_keys($_parsed_query)), rawurlencode_deep(array_values($_parsed_query)));
        $redirect_url = add_query_arg($_parsed_query, $redirect_url);
    }
    if ($redirect_url) {
        $redirect = parse_url($redirect_url);
    }
    // www.example.com vs. example.com
    $user_home = parse_url(home_url());
    if (!empty($user_home['host'])) {
        $redirect['host'] = $user_home['host'];
    }
    if (empty($user_home['path'])) {
        $user_home['path'] = '/';
    }
    // Handle ports.
    if (!empty($user_home['port'])) {
        $redirect['port'] = $user_home['port'];
    } else {
        unset($redirect['port']);
    }
    // Trailing /index.php.
    $redirect['path'] = preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/*?$|', '/', $redirect['path']);
    $punctuation_pattern = implode('|', array_map('preg_quote', array(
        ' ',
        '%20',
        // Space.
        '!',
        '%21',
        // Exclamation mark.
        '"',
        '%22',
        // Double quote.
        "'",
        '%27',
        // Single quote.
        '(',
        '%28',
        // Opening bracket.
        ')',
        '%29',
        // Closing bracket.
        ',',
        '%2C',
        // Comma.
        '.',
        '%2E',
        // Period.
        ';',
        '%3B',
        // Semicolon.
        '{',
        '%7B',
        // Opening curly bracket.
        '}',
        '%7D',
        // Closing curly bracket.
        '%E2%80%9C',
        // Opening curly quote.
        '%E2%80%9D',
    )));
    // Remove trailing spaces and end punctuation from the path.
    $redirect['path'] = preg_replace("#({$punctuation_pattern})+\$#", '', $redirect['path']);
    if (!empty($redirect['query'])) {
        // Remove trailing spaces and end punctuation from certain terminating query string args.
        $redirect['query'] = preg_replace("#((^|&)(p|page_id|cat|tag)=[^&]*?)({$punctuation_pattern})+\$#", '$1', $redirect['query']);
        // Clean up empty query strings.
        $redirect['query'] = trim(preg_replace('#(^|&)(p|page_id|cat|tag)=?(&|$)#', '&', $redirect['query']), '&');
        // Redirect obsolete feeds.
        $redirect['query'] = preg_replace('#(^|&)feed=rss(&|$)#', '$1feed=rss2$2', $redirect['query']);
        // Remove redundant leading ampersands.
        $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    }
    // Strip /index.php/ when we're not using PATHINFO permalinks.
    if (!$wp_rewrite->using_index_permalinks()) {
        $redirect['path'] = str_replace('/' . $wp_rewrite->index . '/', '/', $redirect['path']);
    }
    // Trailing slashes.
    if (is_object($wp_rewrite) && $wp_rewrite->using_permalinks() && !is_404() && (!is_front_page() || is_front_page() && get_query_var('paged') > 1)) {
        $user_ts_type = '';
        if (get_query_var('paged') > 0) {
            $user_ts_type = 'paged';
        } else {
            foreach (array('single', 'category', 'page', 'day', 'month', 'year', 'home') as $type) {
                $func = 'is_' . $type;
                if (call_user_func($func)) {
                    $user_ts_type = $type;
                    break;
                }
            }
        }
        $redirect['path'] = user_trailingslashit($redirect['path'], $user_ts_type);
    } elseif (is_front_page()) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Remove trailing slash for robots.txt or sitemap requests.
    if (is_robots() || !empty(get_query_var('sitemap')) || !empty(get_query_var('sitemap-stylesheet'))) {
        $redirect['path'] = untrailingslashit($redirect['path']);
    }
    // Strip multiple slashes out of the URL.
    if (strpos($redirect['path'], '//') > -1) {
        $redirect['path'] = preg_replace('|/+|', '/', $redirect['path']);
    }
    // Always trailing slash the Front Page URL.
    if (trailingslashit($redirect['path']) === trailingslashit($user_home['path'])) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    $original_host_low = strtolower($original['host']);
    $redirect_host_low = strtolower($redirect['host']);
    // Ignore differences in host capitalization, as this can lead to infinite redirects.
    // Only redirect no-www <=> yes-www.
    if ($original_host_low === $redirect_host_low || 'www.' . $original_host_low !== $redirect_host_low && 'www.' . $redirect_host_low !== $original_host_low) {
        $redirect['host'] = $original['host'];
    }
    $compare_original = array($original['host'], $original['path']);
    if (!empty($original['port'])) {
        $compare_original[] = $original['port'];
    }
    if (!empty($original['query'])) {
        $compare_original[] = $original['query'];
    }
    $compare_redirect = array($redirect['host'], $redirect['path']);
    if (!empty($redirect['port'])) {
        $compare_redirect[] = $redirect['port'];
    }
    if (!empty($redirect['query'])) {
        $compare_redirect[] = $redirect['query'];
    }
    if ($compare_original !== $compare_redirect) {
        $redirect_url = $redirect['scheme'] . '://' . $redirect['host'];
        if (!empty($redirect['port'])) {
            $redirect_url .= ':' . $redirect['port'];
        }
        $redirect_url .= $redirect['path'];
        if (!empty($redirect['query'])) {
            $redirect_url .= '?' . $redirect['query'];
        }
    }
    if (!$redirect_url || $redirect_url === $requested_url) {
        return;
    }
    // Hex encoded octets are case-insensitive.
    if (false !== strpos($requested_url, '%')) {
        if (!function_exists('lowercase_octets')) {
            /**
             * Converts the first hex-encoded octet match to lowercase.
             *
             * @since 3.1.0
             * @ignore
             *
             * @param array $matches Hex-encoded octet matches for the requested URL.
             * @return string Lowercased version of the first match.
             */
            function lowercase_octets($matches)
            {
                return strtolower($matches[0]);
            }
        }
        $requested_url = preg_replace_callback('|%[a-fA-F0-9][a-fA-F0-9]|', 'lowercase_octets', $requested_url);
    }
    /**
     * Filters the canonical redirect URL.
     *
     * Returning false to this filter will cancel the redirect.
     *
     * @since 2.3.0
     *
     * @param string $redirect_url  The redirect URL.
     * @param string $requested_url The requested URL.
     */
    $redirect_url = apply_filters('redirect_canonical', $redirect_url, $requested_url);
    // Yes, again -- in case the filter aborted the request.
    if (!$redirect_url || strip_fragment_from_url($redirect_url) === strip_fragment_from_url($requested_url)) {
        return;
    }
    if ($do_redirect) {
        // Protect against chained redirects.
        if (!redirect_canonical($redirect_url, false)) {
            wp_redirect($redirect_url, 301);
            exit;
        } else {
            // Debug.
            // die("1: $redirect_url<br />2: " . redirect_canonical( $redirect_url, false ) );
            return;
        }
    } else {
        return $redirect_url;
    }
}

WordPress Version: 5.4

/**
 * Canonical API to handle WordPress Redirecting
 *
 * Based on "Permalink Redirect" from Scott Yang and "Enforce www. Preference"
 * by Mark Jaquith
 *
 * @package WordPress
 * @since 2.3.0
 */
/**
 * Redirects incoming links to the proper URL based on the site url.
 *
 * Search engines consider www.somedomain.com and somedomain.com to be two
 * different URLs when they both go to the same location. This SEO enhancement
 * prevents penalty for duplicate content by redirecting all incoming links to
 * one or the other.
 *
 * Prevents redirection for feeds, trackbacks, searches, and
 * admin URLs. Does not redirect on non-pretty-permalink-supporting IIS 7+,
 * page/post previews, WP admin, Trackbacks, robots.txt, favicon.ico, searches,
 * or on POST requests.
 *
 * Will also attempt to find the correct link when a user enters a URL that does
 * not exist based on exact WordPress query. Will instead try to parse the URL
 * or query in an attempt to figure the correct page to go to.
 *
 * @since 2.3.0
 *
 * @global WP_Rewrite $wp_rewrite WordPress rewrite component.
 * @global bool       $is_IIS
 * @global WP_Query   $wp_query   WordPress Query object.
 * @global wpdb       $wpdb       WordPress database abstraction object.
 * @global WP         $wp         Current WordPress environment instance.
 *
 * @param string $requested_url Optional. The URL that was requested, used to
 *      figure if redirect is needed.
 * @param bool $do_redirect Optional. Redirect to the new URL.
 * @return string|void The string of the URL, if redirect needed.
 */
function redirect_canonical($requested_url = null, $do_redirect = true)
{
    global $wp_rewrite, $is_IIS, $wp_query, $wpdb, $wp;
    if (isset($_SERVER['REQUEST_METHOD']) && !in_array(strtoupper($_SERVER['REQUEST_METHOD']), array('GET', 'HEAD'))) {
        return;
    }
    // If we're not in wp-admin and the post has been published and preview nonce
    // is non-existent or invalid then no need for preview in query.
    if (is_preview() && get_query_var('p') && 'publish' == get_post_status(get_query_var('p'))) {
        if (!isset($_GET['preview_id']) || !isset($_GET['preview_nonce']) || !wp_verify_nonce($_GET['preview_nonce'], 'post_preview_' . (int) $_GET['preview_id'])) {
            $wp_query->is_preview = false;
        }
    }
    if (is_trackback() || is_search() || is_admin() || is_preview() || is_robots() || is_favicon() || $is_IIS && !iis7_supports_permalinks()) {
        return;
    }
    if (!$requested_url && isset($_SERVER['HTTP_HOST'])) {
        // Build the URL in the address bar.
        $requested_url = is_ssl() ? 'https://' : 'http://';
        $requested_url .= $_SERVER['HTTP_HOST'];
        $requested_url .= $_SERVER['REQUEST_URI'];
    }
    $original = @parse_url($requested_url);
    if (false === $original) {
        return;
    }
    $redirect = $original;
    $redirect_url = false;
    // Notice fixing.
    if (!isset($redirect['path'])) {
        $redirect['path'] = '';
    }
    if (!isset($redirect['query'])) {
        $redirect['query'] = '';
    }
    /*
     * If the original URL ended with non-breaking spaces, they were almost
     * certainly inserted by accident. Let's remove them, so the reader doesn't
     * see a 404 error with no obvious cause.
     */
    $redirect['path'] = preg_replace('|(%C2%A0)+$|i', '', $redirect['path']);
    // It's not a preview, so remove it from URL.
    if (get_query_var('preview')) {
        $redirect['query'] = remove_query_arg('preview', $redirect['query']);
    }
    $id = get_query_var('p');
    if (is_feed() && $id) {
        $redirect_url = get_post_comments_feed_link($id, get_query_var('feed'));
        if ($redirect_url) {
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type', 'feed'), $redirect_url);
            $redirect['path'] = parse_url($redirect_url, PHP_URL_PATH);
        }
    }
    if (is_singular() && 1 > $wp_query->post_count && $id) {
        $vars = $wpdb->get_results($wpdb->prepare("SELECT post_type, post_parent FROM {$wpdb->posts} WHERE ID = %d", $id));
        if (!empty($vars[0])) {
            $vars = $vars[0];
            if ('revision' == $vars->post_type && $vars->post_parent > 0) {
                $id = $vars->post_parent;
            }
            $redirect_url = get_permalink($id);
            if ($redirect_url) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    }
    // These tests give us a WP-generated permalink.
    if (is_404()) {
        // Redirect ?page_id, ?p=, ?attachment_id= to their respective URLs.
        $id = max(get_query_var('p'), get_query_var('page_id'), get_query_var('attachment_id'));
        $redirect_post = $id ? get_post($id) : false;
        if ($redirect_post) {
            $post_type_obj = get_post_type_object($redirect_post->post_type);
            if ($post_type_obj->public && 'auto-draft' != $redirect_post->post_status) {
                $redirect_url = get_permalink($redirect_post);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
        if (get_query_var('day') && get_query_var('monthnum') && get_query_var('year')) {
            $year = get_query_var('year');
            $month = get_query_var('monthnum');
            $day = get_query_var('day');
            $date = sprintf('%04d-%02d-%02d', $year, $month, $day);
            if (!wp_checkdate($month, $day, $year, $date)) {
                $redirect_url = get_month_link($year, $month);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum', 'day'), $redirect_url);
            }
        } elseif (get_query_var('monthnum') && get_query_var('year') && 12 < get_query_var('monthnum')) {
            $redirect_url = get_year_link(get_query_var('year'));
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum'), $redirect_url);
        }
        if (!$redirect_url) {
            $redirect_url = redirect_guess_404_permalink();
            if ($redirect_url) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('page', 'feed', 'p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
        if (get_query_var('page') && $wp_query->post && false !== strpos($wp_query->post->post_content, '<!--nextpage-->')) {
            $redirect['path'] = rtrim($redirect['path'], (int) get_query_var('page') . '/');
            $redirect['query'] = remove_query_arg('page', $redirect['query']);
            $redirect_url = get_permalink($wp_query->post->ID);
        }
    } elseif (is_object($wp_rewrite) && $wp_rewrite->using_permalinks()) {
        // Rewriting of old ?p=X, ?m=2004, ?m=200401, ?m=20040101.
        if (is_attachment() && !array_diff(array_keys($wp->query_vars), array('attachment', 'attachment_id')) && !$redirect_url) {
            if (!empty($_GET['attachment_id'])) {
                $redirect_url = get_attachment_link(get_query_var('attachment_id'));
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('attachment_id', $redirect['query']);
                }
            } else {
                $redirect_url = get_attachment_link();
            }
        } elseif (is_single() && !empty($_GET['p']) && !$redirect_url) {
            $redirect_url = get_permalink(get_query_var('p'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg(array('p', 'post_type'), $redirect['query']);
            }
        } elseif (is_single() && !empty($_GET['name']) && !$redirect_url) {
            $redirect_url = get_permalink($wp_query->get_queried_object_id());
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('name', $redirect['query']);
            }
        } elseif (is_page() && !empty($_GET['page_id']) && !$redirect_url) {
            $redirect_url = get_permalink(get_query_var('page_id'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (is_page() && !is_feed() && 'page' == get_option('show_on_front') && get_queried_object_id() == get_option('page_on_front') && !$redirect_url) {
            $redirect_url = home_url('/');
        } elseif (is_home() && !empty($_GET['page_id']) && 'page' == get_option('show_on_front') && get_query_var('page_id') == get_option('page_for_posts') && !$redirect_url) {
            $redirect_url = get_permalink(get_option('page_for_posts'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (!empty($_GET['m']) && (is_year() || is_month() || is_day())) {
            $m = get_query_var('m');
            switch (strlen($m)) {
                case 4:
                    // Yearly.
                    $redirect_url = get_year_link($m);
                    break;
                case 6:
                    // Monthly.
                    $redirect_url = get_month_link(substr($m, 0, 4), substr($m, 4, 2));
                    break;
                case 8:
                    // Daily.
                    $redirect_url = get_day_link(substr($m, 0, 4), substr($m, 4, 2), substr($m, 6, 2));
                    break;
            }
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('m', $redirect['query']);
            }
            // Now moving on to non ?m=X year/month/day links.
        } elseif (is_day() && get_query_var('year') && get_query_var('monthnum') && !empty($_GET['day'])) {
            $redirect_url = get_day_link(get_query_var('year'), get_query_var('monthnum'), get_query_var('day'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg(array('year', 'monthnum', 'day'), $redirect['query']);
            }
        } elseif (is_month() && get_query_var('year') && !empty($_GET['monthnum'])) {
            $redirect_url = get_month_link(get_query_var('year'), get_query_var('monthnum'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg(array('year', 'monthnum'), $redirect['query']);
            }
        } elseif (is_year() && !empty($_GET['year'])) {
            $redirect_url = get_year_link(get_query_var('year'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('year', $redirect['query']);
            }
        } elseif (is_author() && !empty($_GET['author']) && preg_match('|^[0-9]+$|', $_GET['author'])) {
            $author = get_userdata(get_query_var('author'));
            if (false !== $author && $wpdb->get_var($wpdb->prepare("SELECT ID FROM {$wpdb->posts} WHERE {$wpdb->posts}.post_author = %d AND {$wpdb->posts}.post_status = 'publish' LIMIT 1", $author->ID))) {
                $redirect_url = get_author_posts_url($author->ID, $author->user_nicename);
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('author', $redirect['query']);
                }
            }
        } elseif (is_category() || is_tag() || is_tax()) {
            // Terms (tags/categories).
            $term_count = 0;
            foreach ($wp_query->tax_query->queried_terms as $tax_query) {
                $term_count += count($tax_query['terms']);
            }
            $obj = $wp_query->get_queried_object();
            if ($term_count <= 1 && !empty($obj->term_id)) {
                $tax_url = get_term_link((int) $obj->term_id, $obj->taxonomy);
                if ($tax_url && !is_wp_error($tax_url)) {
                    if (!empty($redirect['query'])) {
                        // Strip taxonomy query vars off the URL.
                        $qv_remove = array('term', 'taxonomy');
                        if (is_category()) {
                            $qv_remove[] = 'category_name';
                            $qv_remove[] = 'cat';
                        } elseif (is_tag()) {
                            $qv_remove[] = 'tag';
                            $qv_remove[] = 'tag_id';
                        } else {
                            // Custom taxonomies will have a custom query var, remove those too.
                            $tax_obj = get_taxonomy($obj->taxonomy);
                            if (false !== $tax_obj->query_var) {
                                $qv_remove[] = $tax_obj->query_var;
                            }
                        }
                        $rewrite_vars = array_diff(array_keys($wp_query->query), array_keys($_GET));
                        // Check to see if all the query vars are coming from the rewrite, none are set via $_GET.
                        if (!array_diff($rewrite_vars, array_keys($_GET))) {
                            // Remove all of the per-tax query vars.
                            $redirect['query'] = remove_query_arg($qv_remove, $redirect['query']);
                            // Create the destination URL for this taxonomy.
                            $tax_url = parse_url($tax_url);
                            if (!empty($tax_url['query'])) {
                                // Taxonomy accessible via ?taxonomy=...&term=... or any custom query var.
                                parse_str($tax_url['query'], $query_vars);
                                $redirect['query'] = add_query_arg($query_vars, $redirect['query']);
                            } else {
                                // Taxonomy is accessible via a "pretty URL".
                                $redirect['path'] = $tax_url['path'];
                            }
                        } else {
                            // Some query vars are set via $_GET. Unset those from $_GET that exist via the rewrite.
                            foreach ($qv_remove as $_qv) {
                                if (isset($rewrite_vars[$_qv])) {
                                    $redirect['query'] = remove_query_arg($_qv, $redirect['query']);
                                }
                            }
                        }
                    }
                }
            }
        } elseif (is_single() && strpos($wp_rewrite->permalink_structure, '%category%') !== false) {
            $cat = get_query_var('category_name');
            if ($cat) {
                $category = get_category_by_path($cat);
                if (!$category || is_wp_error($category) || !has_term($category->term_id, 'category', $wp_query->get_queried_object_id())) {
                    $redirect_url = get_permalink($wp_query->get_queried_object_id());
                }
            }
        }
        // Post paging.
        if (is_singular() && get_query_var('page')) {
            if (!$redirect_url) {
                $redirect_url = get_permalink(get_queried_object_id());
            }
            $page = get_query_var('page');
            if ($page > 1) {
                if (is_front_page()) {
                    $redirect_url = trailingslashit($redirect_url) . user_trailingslashit("{$wp_rewrite->pagination_base}/{$page}", 'paged');
                } else {
                    $redirect_url = trailingslashit($redirect_url) . user_trailingslashit($page, 'single_paged');
                }
            }
            $redirect['query'] = remove_query_arg('page', $redirect['query']);
        }
        // Paging and feeds.
        if (get_query_var('paged') || is_feed() || get_query_var('cpage')) {
            while (preg_match("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", $redirect['path']) || preg_match('#/(comments/?)?(feed|rss|rdf|atom|rss2)(/+)?$#', $redirect['path']) || preg_match("#/{$wp_rewrite->comments_pagination_base}-[0-9]+(/+)?\$#", $redirect['path'])) {
                // Strip off paging and feed.
                $redirect['path'] = preg_replace("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", '/', $redirect['path']);
                // Strip off any existing paging.
                $redirect['path'] = preg_replace('#/(comments/?)?(feed|rss2?|rdf|atom)(/+|$)#', '/', $redirect['path']);
                // Strip off feed endings.
                $redirect['path'] = preg_replace("#/{$wp_rewrite->comments_pagination_base}-[0-9]+?(/+)?\$#", '/', $redirect['path']);
                // Strip off any existing comment paging.
            }
            $addl_path = '';
            if (is_feed() && in_array(get_query_var('feed'), $wp_rewrite->feeds)) {
                $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                if (!is_singular() && get_query_var('withcomments')) {
                    $addl_path .= 'comments/';
                }
                if ('rss' == get_default_feed() && 'feed' == get_query_var('feed') || 'rss' == get_query_var('feed')) {
                    $addl_path .= user_trailingslashit('feed/' . ((get_default_feed() == 'rss2') ? '' : 'rss2'), 'feed');
                } else {
                    $addl_path .= user_trailingslashit('feed/' . ((get_default_feed() == get_query_var('feed') || 'feed' == get_query_var('feed')) ? '' : get_query_var('feed')), 'feed');
                }
                $redirect['query'] = remove_query_arg('feed', $redirect['query']);
            } elseif (is_feed() && 'old' == get_query_var('feed')) {
                $old_feed_files = array('wp-atom.php' => 'atom', 'wp-commentsrss2.php' => 'comments_rss2', 'wp-feed.php' => get_default_feed(), 'wp-rdf.php' => 'rdf', 'wp-rss.php' => 'rss2', 'wp-rss2.php' => 'rss2');
                if (isset($old_feed_files[basename($redirect['path'])])) {
                    $redirect_url = get_feed_link($old_feed_files[basename($redirect['path'])]);
                    wp_redirect($redirect_url, 301);
                    die;
                }
            }
            if (get_query_var('paged') > 0) {
                $paged = get_query_var('paged');
                $redirect['query'] = remove_query_arg('paged', $redirect['query']);
                if (!is_feed()) {
                    if ($paged > 1 && !is_single()) {
                        $addl_path = ((!empty($addl_path)) ? trailingslashit($addl_path) : '') . user_trailingslashit("{$wp_rewrite->pagination_base}/{$paged}", 'paged');
                    } elseif (!is_single()) {
                        $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                    }
                } elseif ($paged > 1) {
                    $redirect['query'] = add_query_arg('paged', $paged, $redirect['query']);
                }
            }
            if (get_option('page_comments') && ('newest' == get_option('default_comments_page') && get_query_var('cpage') > 0 || 'newest' != get_option('default_comments_page') && get_query_var('cpage') > 1)) {
                $addl_path = ((!empty($addl_path)) ? trailingslashit($addl_path) : '') . user_trailingslashit($wp_rewrite->comments_pagination_base . '-' . get_query_var('cpage'), 'commentpaged');
                $redirect['query'] = remove_query_arg('cpage', $redirect['query']);
            }
            $redirect['path'] = user_trailingslashit(preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/?$|', '/', $redirect['path']));
            // Strip off trailing /index.php/.
            if (!empty($addl_path) && $wp_rewrite->using_index_permalinks() && strpos($redirect['path'], '/' . $wp_rewrite->index . '/') === false) {
                $redirect['path'] = trailingslashit($redirect['path']) . $wp_rewrite->index . '/';
            }
            if (!empty($addl_path)) {
                $redirect['path'] = trailingslashit($redirect['path']) . $addl_path;
            }
            $redirect_url = $redirect['scheme'] . '://' . $redirect['host'] . $redirect['path'];
        }
        if ('wp-register.php' == basename($redirect['path'])) {
            if (is_multisite()) {
                /** This filter is documented in wp-login.php */
                $redirect_url = apply_filters('wp_signup_location', network_site_url('wp-signup.php'));
            } else {
                $redirect_url = wp_registration_url();
            }
            wp_redirect($redirect_url, 301);
            die;
        }
    }
    // Tack on any additional query vars.
    $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    if ($redirect_url && !empty($redirect['query'])) {
        parse_str($redirect['query'], $_parsed_query);
        $redirect = @parse_url($redirect_url);
        if (!empty($_parsed_query['name']) && !empty($redirect['query'])) {
            parse_str($redirect['query'], $_parsed_redirect_query);
            if (empty($_parsed_redirect_query['name'])) {
                unset($_parsed_query['name']);
            }
        }
        $_parsed_query = array_combine(rawurlencode_deep(array_keys($_parsed_query)), rawurlencode_deep(array_values($_parsed_query)));
        $redirect_url = add_query_arg($_parsed_query, $redirect_url);
    }
    if ($redirect_url) {
        $redirect = @parse_url($redirect_url);
    }
    // www.example.com vs. example.com
    $user_home = @parse_url(home_url());
    if (!empty($user_home['host'])) {
        $redirect['host'] = $user_home['host'];
    }
    if (empty($user_home['path'])) {
        $user_home['path'] = '/';
    }
    // Handle ports.
    if (!empty($user_home['port'])) {
        $redirect['port'] = $user_home['port'];
    } else {
        unset($redirect['port']);
    }
    // Trailing /index.php.
    $redirect['path'] = preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/*?$|', '/', $redirect['path']);
    $punctuation_pattern = implode('|', array_map('preg_quote', array(
        ' ',
        '%20',
        // Space.
        '!',
        '%21',
        // Exclamation mark.
        '"',
        '%22',
        // Double quote.
        "'",
        '%27',
        // Single quote.
        '(',
        '%28',
        // Opening bracket.
        ')',
        '%29',
        // Closing bracket.
        ',',
        '%2C',
        // Comma.
        '.',
        '%2E',
        // Period.
        ';',
        '%3B',
        // Semicolon.
        '{',
        '%7B',
        // Opening curly bracket.
        '}',
        '%7D',
        // Closing curly bracket.
        '%E2%80%9C',
        // Opening curly quote.
        '%E2%80%9D',
    )));
    // Remove trailing spaces and end punctuation from the path.
    $redirect['path'] = preg_replace("#({$punctuation_pattern})+\$#", '', $redirect['path']);
    if (!empty($redirect['query'])) {
        // Remove trailing spaces and end punctuation from certain terminating query string args.
        $redirect['query'] = preg_replace("#((^|&)(p|page_id|cat|tag)=[^&]*?)({$punctuation_pattern})+\$#", '$1', $redirect['query']);
        // Clean up empty query strings.
        $redirect['query'] = trim(preg_replace('#(^|&)(p|page_id|cat|tag)=?(&|$)#', '&', $redirect['query']), '&');
        // Redirect obsolete feeds.
        $redirect['query'] = preg_replace('#(^|&)feed=rss(&|$)#', '$1feed=rss2$2', $redirect['query']);
        // Remove redundant leading ampersands.
        $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    }
    // Strip /index.php/ when we're not using PATHINFO permalinks.
    if (!$wp_rewrite->using_index_permalinks()) {
        $redirect['path'] = str_replace('/' . $wp_rewrite->index . '/', '/', $redirect['path']);
    }
    // Trailing slashes.
    if (is_object($wp_rewrite) && $wp_rewrite->using_permalinks() && !is_404() && (!is_front_page() || is_front_page() && get_query_var('paged') > 1)) {
        $user_ts_type = '';
        if (get_query_var('paged') > 0) {
            $user_ts_type = 'paged';
        } else {
            foreach (array('single', 'category', 'page', 'day', 'month', 'year', 'home') as $type) {
                $func = 'is_' . $type;
                if (call_user_func($func)) {
                    $user_ts_type = $type;
                    break;
                }
            }
        }
        $redirect['path'] = user_trailingslashit($redirect['path'], $user_ts_type);
    } elseif (is_front_page()) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Strip multiple slashes out of the URL.
    if (strpos($redirect['path'], '//') > -1) {
        $redirect['path'] = preg_replace('|/+|', '/', $redirect['path']);
    }
    // Always trailing slash the Front Page URL.
    if (trailingslashit($redirect['path']) == trailingslashit($user_home['path'])) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Ignore differences in host capitalization, as this can lead to infinite redirects.
    // Only redirect no-www <=> yes-www.
    if (strtolower($original['host']) == strtolower($redirect['host']) || strtolower($original['host']) != 'www.' . strtolower($redirect['host']) && 'www.' . strtolower($original['host']) != strtolower($redirect['host'])) {
        $redirect['host'] = $original['host'];
    }
    $compare_original = array($original['host'], $original['path']);
    if (!empty($original['port'])) {
        $compare_original[] = $original['port'];
    }
    if (!empty($original['query'])) {
        $compare_original[] = $original['query'];
    }
    $compare_redirect = array($redirect['host'], $redirect['path']);
    if (!empty($redirect['port'])) {
        $compare_redirect[] = $redirect['port'];
    }
    if (!empty($redirect['query'])) {
        $compare_redirect[] = $redirect['query'];
    }
    if ($compare_original !== $compare_redirect) {
        $redirect_url = $redirect['scheme'] . '://' . $redirect['host'];
        if (!empty($redirect['port'])) {
            $redirect_url .= ':' . $redirect['port'];
        }
        $redirect_url .= $redirect['path'];
        if (!empty($redirect['query'])) {
            $redirect_url .= '?' . $redirect['query'];
        }
    }
    if (!$redirect_url || $redirect_url == $requested_url) {
        return;
    }
    // Hex encoded octets are case-insensitive.
    if (false !== strpos($requested_url, '%')) {
        if (!function_exists('lowercase_octets')) {
            /**
             * Converts the first hex-encoded octet match to lowercase.
             *
             * @since 3.1.0
             * @ignore
             *
             * @param array $matches Hex-encoded octet matches for the requested URL.
             * @return string Lowercased version of the first match.
             */
            function lowercase_octets($matches)
            {
                return strtolower($matches[0]);
            }
        }
        $requested_url = preg_replace_callback('|%[a-fA-F0-9][a-fA-F0-9]|', 'lowercase_octets', $requested_url);
    }
    /**
     * Filters the canonical redirect URL.
     *
     * Returning false to this filter will cancel the redirect.
     *
     * @since 2.3.0
     *
     * @param string $redirect_url  The redirect URL.
     * @param string $requested_url The requested URL.
     */
    $redirect_url = apply_filters('redirect_canonical', $redirect_url, $requested_url);
    // Yes, again -- in case the filter aborted the request.
    if (!$redirect_url || strip_fragment_from_url($redirect_url) == strip_fragment_from_url($requested_url)) {
        return;
    }
    if ($do_redirect) {
        // Protect against chained redirects.
        if (!redirect_canonical($redirect_url, false)) {
            wp_redirect($redirect_url, 301);
            exit;
        } else {
            // Debug.
            // die("1: $redirect_url<br />2: " . redirect_canonical( $redirect_url, false ) );
            return;
        }
    } else {
        return $redirect_url;
    }
}

WordPress Version: 5.3

/**
 * Canonical API to handle WordPress Redirecting
 *
 * Based on "Permalink Redirect" from Scott Yang and "Enforce www. Preference"
 * by Mark Jaquith
 *
 * @package WordPress
 * @since 2.3.0
 */
/**
 * Redirects incoming links to the proper URL based on the site url.
 *
 * Search engines consider www.somedomain.com and somedomain.com to be two
 * different URLs when they both go to the same location. This SEO enhancement
 * prevents penalty for duplicate content by redirecting all incoming links to
 * one or the other.
 *
 * Prevents redirection for feeds, trackbacks, searches, and
 * admin URLs. Does not redirect on non-pretty-permalink-supporting IIS 7+,
 * page/post previews, WP admin, Trackbacks, robots.txt, searches, or on POST
 * requests.
 *
 * Will also attempt to find the correct link when a user enters a URL that does
 * not exist based on exact WordPress query. Will instead try to parse the URL
 * or query in an attempt to figure the correct page to go to.
 *
 * @since 2.3.0
 *
 * @global WP_Rewrite $wp_rewrite WordPress rewrite component.
 * @global bool       $is_IIS
 * @global WP_Query   $wp_query   WordPress Query object.
 * @global wpdb       $wpdb       WordPress database abstraction object.
 * @global WP         $wp         Current WordPress environment instance.
 *
 * @param string $requested_url Optional. The URL that was requested, used to
 *      figure if redirect is needed.
 * @param bool $do_redirect Optional. Redirect to the new URL.
 * @return string|void The string of the URL, if redirect needed.
 */
function redirect_canonical($requested_url = null, $do_redirect = true)
{
    global $wp_rewrite, $is_IIS, $wp_query, $wpdb, $wp;
    if (isset($_SERVER['REQUEST_METHOD']) && !in_array(strtoupper($_SERVER['REQUEST_METHOD']), array('GET', 'HEAD'))) {
        return;
    }
    // If we're not in wp-admin and the post has been published and preview nonce
    // is non-existent or invalid then no need for preview in query
    if (is_preview() && get_query_var('p') && 'publish' == get_post_status(get_query_var('p'))) {
        if (!isset($_GET['preview_id']) || !isset($_GET['preview_nonce']) || !wp_verify_nonce($_GET['preview_nonce'], 'post_preview_' . (int) $_GET['preview_id'])) {
            $wp_query->is_preview = false;
        }
    }
    if (is_trackback() || is_search() || is_admin() || is_preview() || is_robots() || $is_IIS && !iis7_supports_permalinks()) {
        return;
    }
    if (!$requested_url && isset($_SERVER['HTTP_HOST'])) {
        // build the URL in the address bar
        $requested_url = is_ssl() ? 'https://' : 'http://';
        $requested_url .= $_SERVER['HTTP_HOST'];
        $requested_url .= $_SERVER['REQUEST_URI'];
    }
    $original = @parse_url($requested_url);
    if (false === $original) {
        return;
    }
    $redirect = $original;
    $redirect_url = false;
    // Notice fixing
    if (!isset($redirect['path'])) {
        $redirect['path'] = '';
    }
    if (!isset($redirect['query'])) {
        $redirect['query'] = '';
    }
    // If the original URL ended with non-breaking spaces, they were almost
    // certainly inserted by accident. Let's remove them, so the reader doesn't
    // see a 404 error with no obvious cause.
    $redirect['path'] = preg_replace('|(%C2%A0)+$|i', '', $redirect['path']);
    // It's not a preview, so remove it from URL
    if (get_query_var('preview')) {
        $redirect['query'] = remove_query_arg('preview', $redirect['query']);
    }
    $id = get_query_var('p');
    if (is_feed() && $id) {
        $redirect_url = get_post_comments_feed_link($id, get_query_var('feed'));
        if ($redirect_url) {
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type', 'feed'), $redirect_url);
            $redirect['path'] = parse_url($redirect_url, PHP_URL_PATH);
        }
    }
    if (is_singular() && 1 > $wp_query->post_count && $id) {
        $vars = $wpdb->get_results($wpdb->prepare("SELECT post_type, post_parent FROM {$wpdb->posts} WHERE ID = %d", $id));
        if (!empty($vars[0])) {
            $vars = $vars[0];
            if ('revision' == $vars->post_type && $vars->post_parent > 0) {
                $id = $vars->post_parent;
            }
            $redirect_url = get_permalink($id);
            if ($redirect_url) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    }
    // These tests give us a WP-generated permalink
    if (is_404()) {
        // Redirect ?page_id, ?p=, ?attachment_id= to their respective url's
        $id = max(get_query_var('p'), get_query_var('page_id'), get_query_var('attachment_id'));
        $redirect_post = $id ? get_post($id) : false;
        if ($redirect_post) {
            $post_type_obj = get_post_type_object($redirect_post->post_type);
            if ($post_type_obj->public && 'auto-draft' != $redirect_post->post_status) {
                $redirect_url = get_permalink($redirect_post);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
        if (get_query_var('day') && get_query_var('monthnum') && get_query_var('year')) {
            $year = get_query_var('year');
            $month = get_query_var('monthnum');
            $day = get_query_var('day');
            $date = sprintf('%04d-%02d-%02d', $year, $month, $day);
            if (!wp_checkdate($month, $day, $year, $date)) {
                $redirect_url = get_month_link($year, $month);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum', 'day'), $redirect_url);
            }
        } elseif (get_query_var('monthnum') && get_query_var('year') && 12 < get_query_var('monthnum')) {
            $redirect_url = get_year_link(get_query_var('year'));
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum'), $redirect_url);
        }
        if (!$redirect_url) {
            $redirect_url = redirect_guess_404_permalink();
            if ($redirect_url) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('page', 'feed', 'p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
        if (get_query_var('page') && $wp_query->post && false !== strpos($wp_query->post->post_content, '<!--nextpage-->')) {
            $redirect['path'] = rtrim($redirect['path'], (int) get_query_var('page') . '/');
            $redirect['query'] = remove_query_arg('page', $redirect['query']);
            $redirect_url = get_permalink($wp_query->post->ID);
        }
    } elseif (is_object($wp_rewrite) && $wp_rewrite->using_permalinks()) {
        // rewriting of old ?p=X, ?m=2004, ?m=200401, ?m=20040101
        if (is_attachment() && !array_diff(array_keys($wp->query_vars), array('attachment', 'attachment_id')) && !$redirect_url) {
            if (!empty($_GET['attachment_id'])) {
                $redirect_url = get_attachment_link(get_query_var('attachment_id'));
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('attachment_id', $redirect['query']);
                }
            } else {
                $redirect_url = get_attachment_link();
            }
        } elseif (is_single() && !empty($_GET['p']) && !$redirect_url) {
            $redirect_url = get_permalink(get_query_var('p'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg(array('p', 'post_type'), $redirect['query']);
            }
        } elseif (is_single() && !empty($_GET['name']) && !$redirect_url) {
            $redirect_url = get_permalink($wp_query->get_queried_object_id());
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('name', $redirect['query']);
            }
        } elseif (is_page() && !empty($_GET['page_id']) && !$redirect_url) {
            $redirect_url = get_permalink(get_query_var('page_id'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (is_page() && !is_feed() && 'page' == get_option('show_on_front') && get_queried_object_id() == get_option('page_on_front') && !$redirect_url) {
            $redirect_url = home_url('/');
        } elseif (is_home() && !empty($_GET['page_id']) && 'page' == get_option('show_on_front') && get_query_var('page_id') == get_option('page_for_posts') && !$redirect_url) {
            $redirect_url = get_permalink(get_option('page_for_posts'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (!empty($_GET['m']) && (is_year() || is_month() || is_day())) {
            $m = get_query_var('m');
            switch (strlen($m)) {
                case 4:
                    // Yearly
                    $redirect_url = get_year_link($m);
                    break;
                case 6:
                    // Monthly
                    $redirect_url = get_month_link(substr($m, 0, 4), substr($m, 4, 2));
                    break;
                case 8:
                    // Daily
                    $redirect_url = get_day_link(substr($m, 0, 4), substr($m, 4, 2), substr($m, 6, 2));
                    break;
            }
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('m', $redirect['query']);
            }
            // now moving on to non ?m=X year/month/day links
        } elseif (is_day() && get_query_var('year') && get_query_var('monthnum') && !empty($_GET['day'])) {
            $redirect_url = get_day_link(get_query_var('year'), get_query_var('monthnum'), get_query_var('day'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg(array('year', 'monthnum', 'day'), $redirect['query']);
            }
        } elseif (is_month() && get_query_var('year') && !empty($_GET['monthnum'])) {
            $redirect_url = get_month_link(get_query_var('year'), get_query_var('monthnum'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg(array('year', 'monthnum'), $redirect['query']);
            }
        } elseif (is_year() && !empty($_GET['year'])) {
            $redirect_url = get_year_link(get_query_var('year'));
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('year', $redirect['query']);
            }
        } elseif (is_author() && !empty($_GET['author']) && preg_match('|^[0-9]+$|', $_GET['author'])) {
            $author = get_userdata(get_query_var('author'));
            if (false !== $author && $wpdb->get_var($wpdb->prepare("SELECT ID FROM {$wpdb->posts} WHERE {$wpdb->posts}.post_author = %d AND {$wpdb->posts}.post_status = 'publish' LIMIT 1", $author->ID))) {
                $redirect_url = get_author_posts_url($author->ID, $author->user_nicename);
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('author', $redirect['query']);
                }
            }
        } elseif (is_category() || is_tag() || is_tax()) {
            // Terms (Tags/categories)
            $term_count = 0;
            foreach ($wp_query->tax_query->queried_terms as $tax_query) {
                $term_count += count($tax_query['terms']);
            }
            $obj = $wp_query->get_queried_object();
            if ($term_count <= 1 && !empty($obj->term_id)) {
                $tax_url = get_term_link((int) $obj->term_id, $obj->taxonomy);
                if ($tax_url && !is_wp_error($tax_url)) {
                    if (!empty($redirect['query'])) {
                        // Strip taxonomy query vars off the url.
                        $qv_remove = array('term', 'taxonomy');
                        if (is_category()) {
                            $qv_remove[] = 'category_name';
                            $qv_remove[] = 'cat';
                        } elseif (is_tag()) {
                            $qv_remove[] = 'tag';
                            $qv_remove[] = 'tag_id';
                        } else {
                            // Custom taxonomies will have a custom query var, remove those too:
                            $tax_obj = get_taxonomy($obj->taxonomy);
                            if (false !== $tax_obj->query_var) {
                                $qv_remove[] = $tax_obj->query_var;
                            }
                        }
                        $rewrite_vars = array_diff(array_keys($wp_query->query), array_keys($_GET));
                        if (!array_diff($rewrite_vars, array_keys($_GET))) {
                            // Check to see if all the Query vars are coming from the rewrite, none are set via $_GET
                            $redirect['query'] = remove_query_arg($qv_remove, $redirect['query']);
                            //Remove all of the per-tax qv's
                            // Create the destination url for this taxonomy
                            $tax_url = parse_url($tax_url);
                            if (!empty($tax_url['query'])) {
                                // Taxonomy accessible via ?taxonomy=..&term=.. or any custom qv..
                                parse_str($tax_url['query'], $query_vars);
                                $redirect['query'] = add_query_arg($query_vars, $redirect['query']);
                            } else {
                                // Taxonomy is accessible via a "pretty-URL"
                                $redirect['path'] = $tax_url['path'];
                            }
                        } else {
                            // Some query vars are set via $_GET. Unset those from $_GET that exist via the rewrite
                            foreach ($qv_remove as $_qv) {
                                if (isset($rewrite_vars[$_qv])) {
                                    $redirect['query'] = remove_query_arg($_qv, $redirect['query']);
                                }
                            }
                        }
                    }
                }
            }
        } elseif (is_single() && strpos($wp_rewrite->permalink_structure, '%category%') !== false) {
            $cat = get_query_var('category_name');
            if ($cat) {
                $category = get_category_by_path($cat);
                if (!$category || is_wp_error($category) || !has_term($category->term_id, 'category', $wp_query->get_queried_object_id())) {
                    $redirect_url = get_permalink($wp_query->get_queried_object_id());
                }
            }
        }
        // Post Paging
        if (is_singular() && get_query_var('page')) {
            if (!$redirect_url) {
                $redirect_url = get_permalink(get_queried_object_id());
            }
            $page = get_query_var('page');
            if ($page > 1) {
                if (is_front_page()) {
                    $redirect_url = trailingslashit($redirect_url) . user_trailingslashit("{$wp_rewrite->pagination_base}/{$page}", 'paged');
                } else {
                    $redirect_url = trailingslashit($redirect_url) . user_trailingslashit($page, 'single_paged');
                }
            }
            $redirect['query'] = remove_query_arg('page', $redirect['query']);
        }
        // paging and feeds
        if (get_query_var('paged') || is_feed() || get_query_var('cpage')) {
            while (preg_match("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", $redirect['path']) || preg_match('#/(comments/?)?(feed|rss|rdf|atom|rss2)(/+)?$#', $redirect['path']) || preg_match("#/{$wp_rewrite->comments_pagination_base}-[0-9]+(/+)?\$#", $redirect['path'])) {
                // Strip off paging and feed
                $redirect['path'] = preg_replace("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", '/', $redirect['path']);
                // strip off any existing paging
                $redirect['path'] = preg_replace('#/(comments/?)?(feed|rss2?|rdf|atom)(/+|$)#', '/', $redirect['path']);
                // strip off feed endings
                $redirect['path'] = preg_replace("#/{$wp_rewrite->comments_pagination_base}-[0-9]+?(/+)?\$#", '/', $redirect['path']);
                // strip off any existing comment paging
            }
            $addl_path = '';
            if (is_feed() && in_array(get_query_var('feed'), $wp_rewrite->feeds)) {
                $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                if (!is_singular() && get_query_var('withcomments')) {
                    $addl_path .= 'comments/';
                }
                if ('rss' == get_default_feed() && 'feed' == get_query_var('feed') || 'rss' == get_query_var('feed')) {
                    $addl_path .= user_trailingslashit('feed/' . ((get_default_feed() == 'rss2') ? '' : 'rss2'), 'feed');
                } else {
                    $addl_path .= user_trailingslashit('feed/' . ((get_default_feed() == get_query_var('feed') || 'feed' == get_query_var('feed')) ? '' : get_query_var('feed')), 'feed');
                }
                $redirect['query'] = remove_query_arg('feed', $redirect['query']);
            } elseif (is_feed() && 'old' == get_query_var('feed')) {
                $old_feed_files = array('wp-atom.php' => 'atom', 'wp-commentsrss2.php' => 'comments_rss2', 'wp-feed.php' => get_default_feed(), 'wp-rdf.php' => 'rdf', 'wp-rss.php' => 'rss2', 'wp-rss2.php' => 'rss2');
                if (isset($old_feed_files[basename($redirect['path'])])) {
                    $redirect_url = get_feed_link($old_feed_files[basename($redirect['path'])]);
                    wp_redirect($redirect_url, 301);
                    die;
                }
            }
            if (get_query_var('paged') > 0) {
                $paged = get_query_var('paged');
                $redirect['query'] = remove_query_arg('paged', $redirect['query']);
                if (!is_feed()) {
                    if ($paged > 1 && !is_single()) {
                        $addl_path = ((!empty($addl_path)) ? trailingslashit($addl_path) : '') . user_trailingslashit("{$wp_rewrite->pagination_base}/{$paged}", 'paged');
                    } elseif (!is_single()) {
                        $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                    }
                } elseif ($paged > 1) {
                    $redirect['query'] = add_query_arg('paged', $paged, $redirect['query']);
                }
            }
            if (get_option('page_comments') && ('newest' == get_option('default_comments_page') && get_query_var('cpage') > 0 || 'newest' != get_option('default_comments_page') && get_query_var('cpage') > 1)) {
                $addl_path = ((!empty($addl_path)) ? trailingslashit($addl_path) : '') . user_trailingslashit($wp_rewrite->comments_pagination_base . '-' . get_query_var('cpage'), 'commentpaged');
                $redirect['query'] = remove_query_arg('cpage', $redirect['query']);
            }
            $redirect['path'] = user_trailingslashit(preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/?$|', '/', $redirect['path']));
            // strip off trailing /index.php/
            if (!empty($addl_path) && $wp_rewrite->using_index_permalinks() && strpos($redirect['path'], '/' . $wp_rewrite->index . '/') === false) {
                $redirect['path'] = trailingslashit($redirect['path']) . $wp_rewrite->index . '/';
            }
            if (!empty($addl_path)) {
                $redirect['path'] = trailingslashit($redirect['path']) . $addl_path;
            }
            $redirect_url = $redirect['scheme'] . '://' . $redirect['host'] . $redirect['path'];
        }
        if ('wp-register.php' == basename($redirect['path'])) {
            if (is_multisite()) {
                /** This filter is documented in wp-login.php */
                $redirect_url = apply_filters('wp_signup_location', network_site_url('wp-signup.php'));
            } else {
                $redirect_url = wp_registration_url();
            }
            wp_redirect($redirect_url, 301);
            die;
        }
    }
    // tack on any additional query vars
    $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    if ($redirect_url && !empty($redirect['query'])) {
        parse_str($redirect['query'], $_parsed_query);
        $redirect = @parse_url($redirect_url);
        if (!empty($_parsed_query['name']) && !empty($redirect['query'])) {
            parse_str($redirect['query'], $_parsed_redirect_query);
            if (empty($_parsed_redirect_query['name'])) {
                unset($_parsed_query['name']);
            }
        }
        $_parsed_query = array_combine(rawurlencode_deep(array_keys($_parsed_query)), rawurlencode_deep(array_values($_parsed_query)));
        $redirect_url = add_query_arg($_parsed_query, $redirect_url);
    }
    if ($redirect_url) {
        $redirect = @parse_url($redirect_url);
    }
    // www.example.com vs example.com
    $user_home = @parse_url(home_url());
    if (!empty($user_home['host'])) {
        $redirect['host'] = $user_home['host'];
    }
    if (empty($user_home['path'])) {
        $user_home['path'] = '/';
    }
    // Handle ports
    if (!empty($user_home['port'])) {
        $redirect['port'] = $user_home['port'];
    } else {
        unset($redirect['port']);
    }
    // trailing /index.php
    $redirect['path'] = preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/*?$|', '/', $redirect['path']);
    $punctuation_pattern = implode('|', array_map('preg_quote', array(
        ' ',
        '%20',
        // space
        '!',
        '%21',
        // exclamation mark
        '"',
        '%22',
        // double quote
        "'",
        '%27',
        // single quote
        '(',
        '%28',
        // opening bracket
        ')',
        '%29',
        // closing bracket
        ',',
        '%2C',
        // comma
        '.',
        '%2E',
        // period
        ';',
        '%3B',
        // semicolon
        '{',
        '%7B',
        // opening curly bracket
        '}',
        '%7D',
        // closing curly bracket
        '%E2%80%9C',
        // opening curly quote
        '%E2%80%9D',
    )));
    // Remove trailing spaces and end punctuation from the path.
    $redirect['path'] = preg_replace("#({$punctuation_pattern})+\$#", '', $redirect['path']);
    if (!empty($redirect['query'])) {
        // Remove trailing spaces and end punctuation from certain terminating query string args.
        $redirect['query'] = preg_replace("#((p|page_id|cat|tag)=[^&]*?)({$punctuation_pattern})+\$#", '$1', $redirect['query']);
        // Clean up empty query strings
        $redirect['query'] = trim(preg_replace('#(^|&)(p|page_id|cat|tag)=?(&|$)#', '&', $redirect['query']), '&');
        // Redirect obsolete feeds
        $redirect['query'] = preg_replace('#(^|&)feed=rss(&|$)#', '$1feed=rss2$2', $redirect['query']);
        // Remove redundant leading ampersands
        $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    }
    // strip /index.php/ when we're not using PATHINFO permalinks
    if (!$wp_rewrite->using_index_permalinks()) {
        $redirect['path'] = str_replace('/' . $wp_rewrite->index . '/', '/', $redirect['path']);
    }
    // trailing slashes
    if (is_object($wp_rewrite) && $wp_rewrite->using_permalinks() && !is_404() && (!is_front_page() || is_front_page() && get_query_var('paged') > 1)) {
        $user_ts_type = '';
        if (get_query_var('paged') > 0) {
            $user_ts_type = 'paged';
        } else {
            foreach (array('single', 'category', 'page', 'day', 'month', 'year', 'home') as $type) {
                $func = 'is_' . $type;
                if (call_user_func($func)) {
                    $user_ts_type = $type;
                    break;
                }
            }
        }
        $redirect['path'] = user_trailingslashit($redirect['path'], $user_ts_type);
    } elseif (is_front_page()) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Strip multiple slashes out of the URL
    if (strpos($redirect['path'], '//') > -1) {
        $redirect['path'] = preg_replace('|/+|', '/', $redirect['path']);
    }
    // Always trailing slash the Front Page URL
    if (trailingslashit($redirect['path']) == trailingslashit($user_home['path'])) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Ignore differences in host capitalization, as this can lead to infinite redirects
    // Only redirect no-www <=> yes-www
    if (strtolower($original['host']) == strtolower($redirect['host']) || strtolower($original['host']) != 'www.' . strtolower($redirect['host']) && 'www.' . strtolower($original['host']) != strtolower($redirect['host'])) {
        $redirect['host'] = $original['host'];
    }
    $compare_original = array($original['host'], $original['path']);
    if (!empty($original['port'])) {
        $compare_original[] = $original['port'];
    }
    if (!empty($original['query'])) {
        $compare_original[] = $original['query'];
    }
    $compare_redirect = array($redirect['host'], $redirect['path']);
    if (!empty($redirect['port'])) {
        $compare_redirect[] = $redirect['port'];
    }
    if (!empty($redirect['query'])) {
        $compare_redirect[] = $redirect['query'];
    }
    if ($compare_original !== $compare_redirect) {
        $redirect_url = $redirect['scheme'] . '://' . $redirect['host'];
        if (!empty($redirect['port'])) {
            $redirect_url .= ':' . $redirect['port'];
        }
        $redirect_url .= $redirect['path'];
        if (!empty($redirect['query'])) {
            $redirect_url .= '?' . $redirect['query'];
        }
    }
    if (!$redirect_url || $redirect_url == $requested_url) {
        return;
    }
    // Hex encoded octets are case-insensitive.
    if (false !== strpos($requested_url, '%')) {
        if (!function_exists('lowercase_octets')) {
            /**
             * Converts the first hex-encoded octet match to lowercase.
             *
             * @since 3.1.0
             * @ignore
             *
             * @param array $matches Hex-encoded octet matches for the requested URL.
             * @return string Lowercased version of the first match.
             */
            function lowercase_octets($matches)
            {
                return strtolower($matches[0]);
            }
        }
        $requested_url = preg_replace_callback('|%[a-fA-F0-9][a-fA-F0-9]|', 'lowercase_octets', $requested_url);
    }
    /**
     * Filters the canonical redirect URL.
     *
     * Returning false to this filter will cancel the redirect.
     *
     * @since 2.3.0
     *
     * @param string $redirect_url  The redirect URL.
     * @param string $requested_url The requested URL.
     */
    $redirect_url = apply_filters('redirect_canonical', $redirect_url, $requested_url);
    // yes, again -- in case the filter aborted the request
    if (!$redirect_url || strip_fragment_from_url($redirect_url) == strip_fragment_from_url($requested_url)) {
        return;
    }
    if ($do_redirect) {
        // protect against chained redirects
        if (!redirect_canonical($redirect_url, false)) {
            wp_redirect($redirect_url, 301);
            exit;
        } else {
            // Debug
            // die("1: $redirect_url<br />2: " . redirect_canonical( $redirect_url, false ) );
            return;
        }
    } else {
        return $redirect_url;
    }
}

WordPress Version: 5.2

/**
 * Canonical API to handle WordPress Redirecting
 *
 * Based on "Permalink Redirect" from Scott Yang and "Enforce www. Preference"
 * by Mark Jaquith
 *
 * @package WordPress
 * @since 2.3.0
 */
/**
 * Redirects incoming links to the proper URL based on the site url.
 *
 * Search engines consider www.somedomain.com and somedomain.com to be two
 * different URLs when they both go to the same location. This SEO enhancement
 * prevents penalty for duplicate content by redirecting all incoming links to
 * one or the other.
 *
 * Prevents redirection for feeds, trackbacks, searches, and
 * admin URLs. Does not redirect on non-pretty-permalink-supporting IIS 7+,
 * page/post previews, WP admin, Trackbacks, robots.txt, searches, or on POST
 * requests.
 *
 * Will also attempt to find the correct link when a user enters a URL that does
 * not exist based on exact WordPress query. Will instead try to parse the URL
 * or query in an attempt to figure the correct page to go to.
 *
 * @since 2.3.0
 *
 * @global WP_Rewrite $wp_rewrite
 * @global bool $is_IIS
 * @global WP_Query $wp_query
 * @global wpdb $wpdb WordPress database abstraction object.
 * @global WP $wp Current WordPress environment instance.
 *
 * @param string $requested_url Optional. The URL that was requested, used to
 *      figure if redirect is needed.
 * @param bool $do_redirect Optional. Redirect to the new URL.
 * @return string|void The string of the URL, if redirect needed.
 */
function redirect_canonical($requested_url = null, $do_redirect = true)
{
    global $wp_rewrite, $is_IIS, $wp_query, $wpdb, $wp;
    if (isset($_SERVER['REQUEST_METHOD']) && !in_array(strtoupper($_SERVER['REQUEST_METHOD']), array('GET', 'HEAD'))) {
        return;
    }
    // If we're not in wp-admin and the post has been published and preview nonce
    // is non-existent or invalid then no need for preview in query
    if (is_preview() && get_query_var('p') && 'publish' == get_post_status(get_query_var('p'))) {
        if (!isset($_GET['preview_id']) || !isset($_GET['preview_nonce']) || !wp_verify_nonce($_GET['preview_nonce'], 'post_preview_' . (int) $_GET['preview_id'])) {
            $wp_query->is_preview = false;
        }
    }
    if (is_trackback() || is_search() || is_admin() || is_preview() || is_robots() || $is_IIS && !iis7_supports_permalinks()) {
        return;
    }
    if (!$requested_url && isset($_SERVER['HTTP_HOST'])) {
        // build the URL in the address bar
        $requested_url = is_ssl() ? 'https://' : 'http://';
        $requested_url .= $_SERVER['HTTP_HOST'];
        $requested_url .= $_SERVER['REQUEST_URI'];
    }
    $original = @parse_url($requested_url);
    if (false === $original) {
        return;
    }
    $redirect = $original;
    $redirect_url = false;
    // Notice fixing
    if (!isset($redirect['path'])) {
        $redirect['path'] = '';
    }
    if (!isset($redirect['query'])) {
        $redirect['query'] = '';
    }
    // If the original URL ended with non-breaking spaces, they were almost
    // certainly inserted by accident. Let's remove them, so the reader doesn't
    // see a 404 error with no obvious cause.
    $redirect['path'] = preg_replace('|(%C2%A0)+$|i', '', $redirect['path']);
    // It's not a preview, so remove it from URL
    if (get_query_var('preview')) {
        $redirect['query'] = remove_query_arg('preview', $redirect['query']);
    }
    if (is_feed() && $id = get_query_var('p')) {
        if ($redirect_url = get_post_comments_feed_link($id, get_query_var('feed'))) {
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type', 'feed'), $redirect_url);
            $redirect['path'] = parse_url($redirect_url, PHP_URL_PATH);
        }
    }
    if (is_singular() && 1 > $wp_query->post_count && $id = get_query_var('p')) {
        $vars = $wpdb->get_results($wpdb->prepare("SELECT post_type, post_parent FROM {$wpdb->posts} WHERE ID = %d", $id));
        if (isset($vars[0]) && $vars = $vars[0]) {
            if ('revision' == $vars->post_type && $vars->post_parent > 0) {
                $id = $vars->post_parent;
            }
            if ($redirect_url = get_permalink($id)) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    }
    // These tests give us a WP-generated permalink
    if (is_404()) {
        // Redirect ?page_id, ?p=, ?attachment_id= to their respective url's
        $id = max(get_query_var('p'), get_query_var('page_id'), get_query_var('attachment_id'));
        if ($id && $redirect_post = get_post($id)) {
            $post_type_obj = get_post_type_object($redirect_post->post_type);
            if ($post_type_obj->public && 'auto-draft' != $redirect_post->post_status) {
                $redirect_url = get_permalink($redirect_post);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
        if (get_query_var('day') && get_query_var('monthnum') && get_query_var('year')) {
            $year = get_query_var('year');
            $month = get_query_var('monthnum');
            $day = get_query_var('day');
            $date = sprintf('%04d-%02d-%02d', $year, $month, $day);
            if (!wp_checkdate($month, $day, $year, $date)) {
                $redirect_url = get_month_link($year, $month);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum', 'day'), $redirect_url);
            }
        } elseif (get_query_var('monthnum') && get_query_var('year') && 12 < get_query_var('monthnum')) {
            $redirect_url = get_year_link(get_query_var('year'));
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum'), $redirect_url);
        }
        if (!$redirect_url) {
            if ($redirect_url = redirect_guess_404_permalink()) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('page', 'feed', 'p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
        if (get_query_var('page') && $wp_query->post && false !== strpos($wp_query->post->post_content, '<!--nextpage-->')) {
            $redirect['path'] = rtrim($redirect['path'], (int) get_query_var('page') . '/');
            $redirect['query'] = remove_query_arg('page', $redirect['query']);
            $redirect_url = get_permalink($wp_query->post->ID);
        }
    } elseif (is_object($wp_rewrite) && $wp_rewrite->using_permalinks()) {
        // rewriting of old ?p=X, ?m=2004, ?m=200401, ?m=20040101
        if (is_attachment() && !array_diff(array_keys($wp->query_vars), array('attachment', 'attachment_id')) && !$redirect_url) {
            if (!empty($_GET['attachment_id'])) {
                $redirect_url = get_attachment_link(get_query_var('attachment_id'));
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('attachment_id', $redirect['query']);
                }
            } else {
                $redirect_url = get_attachment_link();
            }
        } elseif (is_single() && !empty($_GET['p']) && !$redirect_url) {
            if ($redirect_url = get_permalink(get_query_var('p'))) {
                $redirect['query'] = remove_query_arg(array('p', 'post_type'), $redirect['query']);
            }
        } elseif (is_single() && !empty($_GET['name']) && !$redirect_url) {
            if ($redirect_url = get_permalink($wp_query->get_queried_object_id())) {
                $redirect['query'] = remove_query_arg('name', $redirect['query']);
            }
        } elseif (is_page() && !empty($_GET['page_id']) && !$redirect_url) {
            if ($redirect_url = get_permalink(get_query_var('page_id'))) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (is_page() && !is_feed() && 'page' == get_option('show_on_front') && get_queried_object_id() == get_option('page_on_front') && !$redirect_url) {
            $redirect_url = home_url('/');
        } elseif (is_home() && !empty($_GET['page_id']) && 'page' == get_option('show_on_front') && get_query_var('page_id') == get_option('page_for_posts') && !$redirect_url) {
            if ($redirect_url = get_permalink(get_option('page_for_posts'))) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (!empty($_GET['m']) && (is_year() || is_month() || is_day())) {
            $m = get_query_var('m');
            switch (strlen($m)) {
                case 4:
                    // Yearly
                    $redirect_url = get_year_link($m);
                    break;
                case 6:
                    // Monthly
                    $redirect_url = get_month_link(substr($m, 0, 4), substr($m, 4, 2));
                    break;
                case 8:
                    // Daily
                    $redirect_url = get_day_link(substr($m, 0, 4), substr($m, 4, 2), substr($m, 6, 2));
                    break;
            }
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('m', $redirect['query']);
            }
            // now moving on to non ?m=X year/month/day links
        } elseif (is_day() && get_query_var('year') && get_query_var('monthnum') && !empty($_GET['day'])) {
            if ($redirect_url = get_day_link(get_query_var('year'), get_query_var('monthnum'), get_query_var('day'))) {
                $redirect['query'] = remove_query_arg(array('year', 'monthnum', 'day'), $redirect['query']);
            }
        } elseif (is_month() && get_query_var('year') && !empty($_GET['monthnum'])) {
            if ($redirect_url = get_month_link(get_query_var('year'), get_query_var('monthnum'))) {
                $redirect['query'] = remove_query_arg(array('year', 'monthnum'), $redirect['query']);
            }
        } elseif (is_year() && !empty($_GET['year'])) {
            if ($redirect_url = get_year_link(get_query_var('year'))) {
                $redirect['query'] = remove_query_arg('year', $redirect['query']);
            }
        } elseif (is_author() && !empty($_GET['author']) && preg_match('|^[0-9]+$|', $_GET['author'])) {
            $author = get_userdata(get_query_var('author'));
            if (false !== $author && $wpdb->get_var($wpdb->prepare("SELECT ID FROM {$wpdb->posts} WHERE {$wpdb->posts}.post_author = %d AND {$wpdb->posts}.post_status = 'publish' LIMIT 1", $author->ID))) {
                if ($redirect_url = get_author_posts_url($author->ID, $author->user_nicename)) {
                    $redirect['query'] = remove_query_arg('author', $redirect['query']);
                }
            }
        } elseif (is_category() || is_tag() || is_tax()) {
            // Terms (Tags/categories)
            $term_count = 0;
            foreach ($wp_query->tax_query->queried_terms as $tax_query) {
                $term_count += count($tax_query['terms']);
            }
            $obj = $wp_query->get_queried_object();
            if ($term_count <= 1 && !empty($obj->term_id) && ($tax_url = get_term_link((int) $obj->term_id, $obj->taxonomy)) && !is_wp_error($tax_url)) {
                if (!empty($redirect['query'])) {
                    // Strip taxonomy query vars off the url.
                    $qv_remove = array('term', 'taxonomy');
                    if (is_category()) {
                        $qv_remove[] = 'category_name';
                        $qv_remove[] = 'cat';
                    } elseif (is_tag()) {
                        $qv_remove[] = 'tag';
                        $qv_remove[] = 'tag_id';
                    } else {
                        // Custom taxonomies will have a custom query var, remove those too:
                        $tax_obj = get_taxonomy($obj->taxonomy);
                        if (false !== $tax_obj->query_var) {
                            $qv_remove[] = $tax_obj->query_var;
                        }
                    }
                    $rewrite_vars = array_diff(array_keys($wp_query->query), array_keys($_GET));
                    if (!array_diff($rewrite_vars, array_keys($_GET))) {
                        // Check to see if all the Query vars are coming from the rewrite, none are set via $_GET
                        $redirect['query'] = remove_query_arg($qv_remove, $redirect['query']);
                        //Remove all of the per-tax qv's
                        // Create the destination url for this taxonomy
                        $tax_url = parse_url($tax_url);
                        if (!empty($tax_url['query'])) {
                            // Taxonomy accessible via ?taxonomy=..&term=.. or any custom qv..
                            parse_str($tax_url['query'], $query_vars);
                            $redirect['query'] = add_query_arg($query_vars, $redirect['query']);
                        } else {
                            // Taxonomy is accessible via a "pretty-URL"
                            $redirect['path'] = $tax_url['path'];
                        }
                    } else {
                        // Some query vars are set via $_GET. Unset those from $_GET that exist via the rewrite
                        foreach ($qv_remove as $_qv) {
                            if (isset($rewrite_vars[$_qv])) {
                                $redirect['query'] = remove_query_arg($_qv, $redirect['query']);
                            }
                        }
                    }
                }
            }
        } elseif (is_single() && strpos($wp_rewrite->permalink_structure, '%category%') !== false && $cat = get_query_var('category_name')) {
            $category = get_category_by_path($cat);
            if (!$category || is_wp_error($category) || !has_term($category->term_id, 'category', $wp_query->get_queried_object_id())) {
                $redirect_url = get_permalink($wp_query->get_queried_object_id());
            }
        }
        // Post Paging
        if (is_singular() && get_query_var('page')) {
            if (!$redirect_url) {
                $redirect_url = get_permalink(get_queried_object_id());
            }
            $page = get_query_var('page');
            if ($page > 1) {
                if (is_front_page()) {
                    $redirect_url = trailingslashit($redirect_url) . user_trailingslashit("{$wp_rewrite->pagination_base}/{$page}", 'paged');
                } else {
                    $redirect_url = trailingslashit($redirect_url) . user_trailingslashit($page, 'single_paged');
                }
            }
            $redirect['query'] = remove_query_arg('page', $redirect['query']);
        }
        // paging and feeds
        if (get_query_var('paged') || is_feed() || get_query_var('cpage')) {
            while (preg_match("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", $redirect['path']) || preg_match('#/(comments/?)?(feed|rss|rdf|atom|rss2)(/+)?$#', $redirect['path']) || preg_match("#/{$wp_rewrite->comments_pagination_base}-[0-9]+(/+)?\$#", $redirect['path'])) {
                // Strip off paging and feed
                $redirect['path'] = preg_replace("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", '/', $redirect['path']);
                // strip off any existing paging
                $redirect['path'] = preg_replace('#/(comments/?)?(feed|rss2?|rdf|atom)(/+|$)#', '/', $redirect['path']);
                // strip off feed endings
                $redirect['path'] = preg_replace("#/{$wp_rewrite->comments_pagination_base}-[0-9]+?(/+)?\$#", '/', $redirect['path']);
                // strip off any existing comment paging
            }
            $addl_path = '';
            if (is_feed() && in_array(get_query_var('feed'), $wp_rewrite->feeds)) {
                $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                if (!is_singular() && get_query_var('withcomments')) {
                    $addl_path .= 'comments/';
                }
                if ('rss' == get_default_feed() && 'feed' == get_query_var('feed') || 'rss' == get_query_var('feed')) {
                    $addl_path .= user_trailingslashit('feed/' . ((get_default_feed() == 'rss2') ? '' : 'rss2'), 'feed');
                } else {
                    $addl_path .= user_trailingslashit('feed/' . ((get_default_feed() == get_query_var('feed') || 'feed' == get_query_var('feed')) ? '' : get_query_var('feed')), 'feed');
                }
                $redirect['query'] = remove_query_arg('feed', $redirect['query']);
            } elseif (is_feed() && 'old' == get_query_var('feed')) {
                $old_feed_files = array('wp-atom.php' => 'atom', 'wp-commentsrss2.php' => 'comments_rss2', 'wp-feed.php' => get_default_feed(), 'wp-rdf.php' => 'rdf', 'wp-rss.php' => 'rss2', 'wp-rss2.php' => 'rss2');
                if (isset($old_feed_files[basename($redirect['path'])])) {
                    $redirect_url = get_feed_link($old_feed_files[basename($redirect['path'])]);
                    wp_redirect($redirect_url, 301);
                    die;
                }
            }
            if (get_query_var('paged') > 0) {
                $paged = get_query_var('paged');
                $redirect['query'] = remove_query_arg('paged', $redirect['query']);
                if (!is_feed()) {
                    if ($paged > 1 && !is_single()) {
                        $addl_path = ((!empty($addl_path)) ? trailingslashit($addl_path) : '') . user_trailingslashit("{$wp_rewrite->pagination_base}/{$paged}", 'paged');
                    } elseif (!is_single()) {
                        $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                    }
                } elseif ($paged > 1) {
                    $redirect['query'] = add_query_arg('paged', $paged, $redirect['query']);
                }
            }
            if (get_option('page_comments') && ('newest' == get_option('default_comments_page') && get_query_var('cpage') > 0 || 'newest' != get_option('default_comments_page') && get_query_var('cpage') > 1)) {
                $addl_path = ((!empty($addl_path)) ? trailingslashit($addl_path) : '') . user_trailingslashit($wp_rewrite->comments_pagination_base . '-' . get_query_var('cpage'), 'commentpaged');
                $redirect['query'] = remove_query_arg('cpage', $redirect['query']);
            }
            $redirect['path'] = user_trailingslashit(preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/?$|', '/', $redirect['path']));
            // strip off trailing /index.php/
            if (!empty($addl_path) && $wp_rewrite->using_index_permalinks() && strpos($redirect['path'], '/' . $wp_rewrite->index . '/') === false) {
                $redirect['path'] = trailingslashit($redirect['path']) . $wp_rewrite->index . '/';
            }
            if (!empty($addl_path)) {
                $redirect['path'] = trailingslashit($redirect['path']) . $addl_path;
            }
            $redirect_url = $redirect['scheme'] . '://' . $redirect['host'] . $redirect['path'];
        }
        if ('wp-register.php' == basename($redirect['path'])) {
            if (is_multisite()) {
                /** This filter is documented in wp-login.php */
                $redirect_url = apply_filters('wp_signup_location', network_site_url('wp-signup.php'));
            } else {
                $redirect_url = wp_registration_url();
            }
            wp_redirect($redirect_url, 301);
            die;
        }
    }
    // tack on any additional query vars
    $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    if ($redirect_url && !empty($redirect['query'])) {
        parse_str($redirect['query'], $_parsed_query);
        $redirect = @parse_url($redirect_url);
        if (!empty($_parsed_query['name']) && !empty($redirect['query'])) {
            parse_str($redirect['query'], $_parsed_redirect_query);
            if (empty($_parsed_redirect_query['name'])) {
                unset($_parsed_query['name']);
            }
        }
        $_parsed_query = array_combine(rawurlencode_deep(array_keys($_parsed_query)), rawurlencode_deep(array_values($_parsed_query)));
        $redirect_url = add_query_arg($_parsed_query, $redirect_url);
    }
    if ($redirect_url) {
        $redirect = @parse_url($redirect_url);
    }
    // www.example.com vs example.com
    $user_home = @parse_url(home_url());
    if (!empty($user_home['host'])) {
        $redirect['host'] = $user_home['host'];
    }
    if (empty($user_home['path'])) {
        $user_home['path'] = '/';
    }
    // Handle ports
    if (!empty($user_home['port'])) {
        $redirect['port'] = $user_home['port'];
    } else {
        unset($redirect['port']);
    }
    // trailing /index.php
    $redirect['path'] = preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/*?$|', '/', $redirect['path']);
    $punctuation_pattern = implode('|', array_map('preg_quote', array(
        ' ',
        '%20',
        // space
        '!',
        '%21',
        // exclamation mark
        '"',
        '%22',
        // double quote
        "'",
        '%27',
        // single quote
        '(',
        '%28',
        // opening bracket
        ')',
        '%29',
        // closing bracket
        ',',
        '%2C',
        // comma
        '.',
        '%2E',
        // period
        ';',
        '%3B',
        // semicolon
        '{',
        '%7B',
        // opening curly bracket
        '}',
        '%7D',
        // closing curly bracket
        '%E2%80%9C',
        // opening curly quote
        '%E2%80%9D',
    )));
    // Remove trailing spaces and end punctuation from the path.
    $redirect['path'] = preg_replace("#({$punctuation_pattern})+\$#", '', $redirect['path']);
    if (!empty($redirect['query'])) {
        // Remove trailing spaces and end punctuation from certain terminating query string args.
        $redirect['query'] = preg_replace("#((p|page_id|cat|tag)=[^&]*?)({$punctuation_pattern})+\$#", '$1', $redirect['query']);
        // Clean up empty query strings
        $redirect['query'] = trim(preg_replace('#(^|&)(p|page_id|cat|tag)=?(&|$)#', '&', $redirect['query']), '&');
        // Redirect obsolete feeds
        $redirect['query'] = preg_replace('#(^|&)feed=rss(&|$)#', '$1feed=rss2$2', $redirect['query']);
        // Remove redundant leading ampersands
        $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    }
    // strip /index.php/ when we're not using PATHINFO permalinks
    if (!$wp_rewrite->using_index_permalinks()) {
        $redirect['path'] = str_replace('/' . $wp_rewrite->index . '/', '/', $redirect['path']);
    }
    // trailing slashes
    if (is_object($wp_rewrite) && $wp_rewrite->using_permalinks() && !is_404() && (!is_front_page() || is_front_page() && get_query_var('paged') > 1)) {
        $user_ts_type = '';
        if (get_query_var('paged') > 0) {
            $user_ts_type = 'paged';
        } else {
            foreach (array('single', 'category', 'page', 'day', 'month', 'year', 'home') as $type) {
                $func = 'is_' . $type;
                if (call_user_func($func)) {
                    $user_ts_type = $type;
                    break;
                }
            }
        }
        $redirect['path'] = user_trailingslashit($redirect['path'], $user_ts_type);
    } elseif (is_front_page()) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Strip multiple slashes out of the URL
    if (strpos($redirect['path'], '//') > -1) {
        $redirect['path'] = preg_replace('|/+|', '/', $redirect['path']);
    }
    // Always trailing slash the Front Page URL
    if (trailingslashit($redirect['path']) == trailingslashit($user_home['path'])) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Ignore differences in host capitalization, as this can lead to infinite redirects
    // Only redirect no-www <=> yes-www
    if (strtolower($original['host']) == strtolower($redirect['host']) || strtolower($original['host']) != 'www.' . strtolower($redirect['host']) && 'www.' . strtolower($original['host']) != strtolower($redirect['host'])) {
        $redirect['host'] = $original['host'];
    }
    $compare_original = array($original['host'], $original['path']);
    if (!empty($original['port'])) {
        $compare_original[] = $original['port'];
    }
    if (!empty($original['query'])) {
        $compare_original[] = $original['query'];
    }
    $compare_redirect = array($redirect['host'], $redirect['path']);
    if (!empty($redirect['port'])) {
        $compare_redirect[] = $redirect['port'];
    }
    if (!empty($redirect['query'])) {
        $compare_redirect[] = $redirect['query'];
    }
    if ($compare_original !== $compare_redirect) {
        $redirect_url = $redirect['scheme'] . '://' . $redirect['host'];
        if (!empty($redirect['port'])) {
            $redirect_url .= ':' . $redirect['port'];
        }
        $redirect_url .= $redirect['path'];
        if (!empty($redirect['query'])) {
            $redirect_url .= '?' . $redirect['query'];
        }
    }
    if (!$redirect_url || $redirect_url == $requested_url) {
        return;
    }
    // Hex encoded octets are case-insensitive.
    if (false !== strpos($requested_url, '%')) {
        if (!function_exists('lowercase_octets')) {
            /**
             * Converts the first hex-encoded octet match to lowercase.
             *
             * @since 3.1.0
             * @ignore
             *
             * @param array $matches Hex-encoded octet matches for the requested URL.
             * @return string Lowercased version of the first match.
             */
            function lowercase_octets($matches)
            {
                return strtolower($matches[0]);
            }
        }
        $requested_url = preg_replace_callback('|%[a-fA-F0-9][a-fA-F0-9]|', 'lowercase_octets', $requested_url);
    }
    /**
     * Filters the canonical redirect URL.
     *
     * Returning false to this filter will cancel the redirect.
     *
     * @since 2.3.0
     *
     * @param string $redirect_url  The redirect URL.
     * @param string $requested_url The requested URL.
     */
    $redirect_url = apply_filters('redirect_canonical', $redirect_url, $requested_url);
    // yes, again -- in case the filter aborted the request
    if (!$redirect_url || strip_fragment_from_url($redirect_url) == strip_fragment_from_url($requested_url)) {
        return;
    }
    if ($do_redirect) {
        // protect against chained redirects
        if (!redirect_canonical($redirect_url, false)) {
            wp_redirect($redirect_url, 301);
            exit;
        } else {
            // Debug
            // die("1: $redirect_url<br />2: " . redirect_canonical( $redirect_url, false ) );
            return;
        }
    } else {
        return $redirect_url;
    }
}

WordPress Version: 5.1

/**
 * Canonical API to handle WordPress Redirecting
 *
 * Based on "Permalink Redirect" from Scott Yang and "Enforce www. Preference"
 * by Mark Jaquith
 *
 * @package WordPress
 * @since 2.3.0
 */
/**
 * Redirects incoming links to the proper URL based on the site url.
 *
 * Search engines consider www.somedomain.com and somedomain.com to be two
 * different URLs when they both go to the same location. This SEO enhancement
 * prevents penalty for duplicate content by redirecting all incoming links to
 * one or the other.
 *
 * Prevents redirection for feeds, trackbacks, searches, and
 * admin URLs. Does not redirect on non-pretty-permalink-supporting IIS 7+,
 * page/post previews, WP admin, Trackbacks, robots.txt, searches, or on POST
 * requests.
 *
 * Will also attempt to find the correct link when a user enters a URL that does
 * not exist based on exact WordPress query. Will instead try to parse the URL
 * or query in an attempt to figure the correct page to go to.
 *
 * @since 2.3.0
 *
 * @global WP_Rewrite $wp_rewrite
 * @global bool $is_IIS
 * @global WP_Query $wp_query
 * @global wpdb $wpdb WordPress database abstraction object.
 * @global WP $wp Current WordPress environment instance.
 *
 * @param string $requested_url Optional. The URL that was requested, used to
 *      figure if redirect is needed.
 * @param bool $do_redirect Optional. Redirect to the new URL.
 * @return string|void The string of the URL, if redirect needed.
 */
function redirect_canonical($requested_url = null, $do_redirect = true)
{
    global $wp_rewrite, $is_IIS, $wp_query, $wpdb, $wp;
    if (isset($_SERVER['REQUEST_METHOD']) && !in_array(strtoupper($_SERVER['REQUEST_METHOD']), array('GET', 'HEAD'))) {
        return;
    }
    // If we're not in wp-admin and the post has been published and preview nonce
    // is non-existent or invalid then no need for preview in query
    if (is_preview() && get_query_var('p') && 'publish' == get_post_status(get_query_var('p'))) {
        if (!isset($_GET['preview_id']) || !isset($_GET['preview_nonce']) || !wp_verify_nonce($_GET['preview_nonce'], 'post_preview_' . (int) $_GET['preview_id'])) {
            $wp_query->is_preview = false;
        }
    }
    if (is_trackback() || is_search() || is_admin() || is_preview() || is_robots() || $is_IIS && !iis7_supports_permalinks()) {
        return;
    }
    if (!$requested_url && isset($_SERVER['HTTP_HOST'])) {
        // build the URL in the address bar
        $requested_url = is_ssl() ? 'https://' : 'http://';
        $requested_url .= $_SERVER['HTTP_HOST'];
        $requested_url .= $_SERVER['REQUEST_URI'];
    }
    $original = @parse_url($requested_url);
    if (false === $original) {
        return;
    }
    $redirect = $original;
    $redirect_url = false;
    // Notice fixing
    if (!isset($redirect['path'])) {
        $redirect['path'] = '';
    }
    if (!isset($redirect['query'])) {
        $redirect['query'] = '';
    }
    // If the original URL ended with non-breaking spaces, they were almost
    // certainly inserted by accident. Let's remove them, so the reader doesn't
    // see a 404 error with no obvious cause.
    $redirect['path'] = preg_replace('|(%C2%A0)+$|i', '', $redirect['path']);
    // It's not a preview, so remove it from URL
    if (get_query_var('preview')) {
        $redirect['query'] = remove_query_arg('preview', $redirect['query']);
    }
    if (is_feed() && $id = get_query_var('p')) {
        if ($redirect_url = get_post_comments_feed_link($id, get_query_var('feed'))) {
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type', 'feed'), $redirect_url);
            $redirect['path'] = parse_url($redirect_url, PHP_URL_PATH);
        }
    }
    if (is_singular() && 1 > $wp_query->post_count && $id = get_query_var('p')) {
        $vars = $wpdb->get_results($wpdb->prepare("SELECT post_type, post_parent FROM {$wpdb->posts} WHERE ID = %d", $id));
        if (isset($vars[0]) && $vars = $vars[0]) {
            if ('revision' == $vars->post_type && $vars->post_parent > 0) {
                $id = $vars->post_parent;
            }
            if ($redirect_url = get_permalink($id)) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    }
    // These tests give us a WP-generated permalink
    if (is_404()) {
        // Redirect ?page_id, ?p=, ?attachment_id= to their respective url's
        $id = max(get_query_var('p'), get_query_var('page_id'), get_query_var('attachment_id'));
        if ($id && $redirect_post = get_post($id)) {
            $post_type_obj = get_post_type_object($redirect_post->post_type);
            if ($post_type_obj->public && 'auto-draft' != $redirect_post->post_status) {
                $redirect_url = get_permalink($redirect_post);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
        if (get_query_var('day') && get_query_var('monthnum') && get_query_var('year')) {
            $year = get_query_var('year');
            $month = get_query_var('monthnum');
            $day = get_query_var('day');
            $date = sprintf('%04d-%02d-%02d', $year, $month, $day);
            if (!wp_checkdate($month, $day, $year, $date)) {
                $redirect_url = get_month_link($year, $month);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum', 'day'), $redirect_url);
            }
        } elseif (get_query_var('monthnum') && get_query_var('year') && 12 < get_query_var('monthnum')) {
            $redirect_url = get_year_link(get_query_var('year'));
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum'), $redirect_url);
        }
        if (!$redirect_url) {
            if ($redirect_url = redirect_guess_404_permalink()) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('page', 'feed', 'p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
        if (get_query_var('page') && $wp_query->post && false !== strpos($wp_query->post->post_content, '<!--nextpage-->')) {
            $redirect['path'] = rtrim($redirect['path'], (int) get_query_var('page') . '/');
            $redirect['query'] = remove_query_arg('page', $redirect['query']);
            $redirect_url = get_permalink($wp_query->post->ID);
        }
    } elseif (is_object($wp_rewrite) && $wp_rewrite->using_permalinks()) {
        // rewriting of old ?p=X, ?m=2004, ?m=200401, ?m=20040101
        if (is_attachment() && !array_diff(array_keys($wp->query_vars), array('attachment', 'attachment_id')) && !$redirect_url) {
            if (!empty($_GET['attachment_id'])) {
                $redirect_url = get_attachment_link(get_query_var('attachment_id'));
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('attachment_id', $redirect['query']);
                }
            } else {
                $redirect_url = get_attachment_link();
            }
        } elseif (is_single() && !empty($_GET['p']) && !$redirect_url) {
            if ($redirect_url = get_permalink(get_query_var('p'))) {
                $redirect['query'] = remove_query_arg(array('p', 'post_type'), $redirect['query']);
            }
        } elseif (is_single() && !empty($_GET['name']) && !$redirect_url) {
            if ($redirect_url = get_permalink($wp_query->get_queried_object_id())) {
                $redirect['query'] = remove_query_arg('name', $redirect['query']);
            }
        } elseif (is_page() && !empty($_GET['page_id']) && !$redirect_url) {
            if ($redirect_url = get_permalink(get_query_var('page_id'))) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (is_page() && !is_feed() && 'page' == get_option('show_on_front') && get_queried_object_id() == get_option('page_on_front') && !$redirect_url) {
            $redirect_url = home_url('/');
        } elseif (is_home() && !empty($_GET['page_id']) && 'page' == get_option('show_on_front') && get_query_var('page_id') == get_option('page_for_posts') && !$redirect_url) {
            if ($redirect_url = get_permalink(get_option('page_for_posts'))) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (!empty($_GET['m']) && (is_year() || is_month() || is_day())) {
            $m = get_query_var('m');
            switch (strlen($m)) {
                case 4:
                    // Yearly
                    $redirect_url = get_year_link($m);
                    break;
                case 6:
                    // Monthly
                    $redirect_url = get_month_link(substr($m, 0, 4), substr($m, 4, 2));
                    break;
                case 8:
                    // Daily
                    $redirect_url = get_day_link(substr($m, 0, 4), substr($m, 4, 2), substr($m, 6, 2));
                    break;
            }
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('m', $redirect['query']);
            }
            // now moving on to non ?m=X year/month/day links
        } elseif (is_day() && get_query_var('year') && get_query_var('monthnum') && !empty($_GET['day'])) {
            if ($redirect_url = get_day_link(get_query_var('year'), get_query_var('monthnum'), get_query_var('day'))) {
                $redirect['query'] = remove_query_arg(array('year', 'monthnum', 'day'), $redirect['query']);
            }
        } elseif (is_month() && get_query_var('year') && !empty($_GET['monthnum'])) {
            if ($redirect_url = get_month_link(get_query_var('year'), get_query_var('monthnum'))) {
                $redirect['query'] = remove_query_arg(array('year', 'monthnum'), $redirect['query']);
            }
        } elseif (is_year() && !empty($_GET['year'])) {
            if ($redirect_url = get_year_link(get_query_var('year'))) {
                $redirect['query'] = remove_query_arg('year', $redirect['query']);
            }
        } elseif (is_author() && !empty($_GET['author']) && preg_match('|^[0-9]+$|', $_GET['author'])) {
            $author = get_userdata(get_query_var('author'));
            if (false !== $author && $wpdb->get_var($wpdb->prepare("SELECT ID FROM {$wpdb->posts} WHERE {$wpdb->posts}.post_author = %d AND {$wpdb->posts}.post_status = 'publish' LIMIT 1", $author->ID))) {
                if ($redirect_url = get_author_posts_url($author->ID, $author->user_nicename)) {
                    $redirect['query'] = remove_query_arg('author', $redirect['query']);
                }
            }
        } elseif (is_category() || is_tag() || is_tax()) {
            // Terms (Tags/categories)
            $term_count = 0;
            foreach ($wp_query->tax_query->queried_terms as $tax_query) {
                $term_count += count($tax_query['terms']);
            }
            $obj = $wp_query->get_queried_object();
            if ($term_count <= 1 && !empty($obj->term_id) && ($tax_url = get_term_link((int) $obj->term_id, $obj->taxonomy)) && !is_wp_error($tax_url)) {
                if (!empty($redirect['query'])) {
                    // Strip taxonomy query vars off the url.
                    $qv_remove = array('term', 'taxonomy');
                    if (is_category()) {
                        $qv_remove[] = 'category_name';
                        $qv_remove[] = 'cat';
                    } elseif (is_tag()) {
                        $qv_remove[] = 'tag';
                        $qv_remove[] = 'tag_id';
                    } else {
                        // Custom taxonomies will have a custom query var, remove those too:
                        $tax_obj = get_taxonomy($obj->taxonomy);
                        if (false !== $tax_obj->query_var) {
                            $qv_remove[] = $tax_obj->query_var;
                        }
                    }
                    $rewrite_vars = array_diff(array_keys($wp_query->query), array_keys($_GET));
                    if (!array_diff($rewrite_vars, array_keys($_GET))) {
                        // Check to see if all the Query vars are coming from the rewrite, none are set via $_GET
                        $redirect['query'] = remove_query_arg($qv_remove, $redirect['query']);
                        //Remove all of the per-tax qv's
                        // Create the destination url for this taxonomy
                        $tax_url = parse_url($tax_url);
                        if (!empty($tax_url['query'])) {
                            // Taxonomy accessible via ?taxonomy=..&term=.. or any custom qv..
                            parse_str($tax_url['query'], $query_vars);
                            $redirect['query'] = add_query_arg($query_vars, $redirect['query']);
                        } else {
                            // Taxonomy is accessible via a "pretty-URL"
                            $redirect['path'] = $tax_url['path'];
                        }
                    } else {
                        // Some query vars are set via $_GET. Unset those from $_GET that exist via the rewrite
                        foreach ($qv_remove as $_qv) {
                            if (isset($rewrite_vars[$_qv])) {
                                $redirect['query'] = remove_query_arg($_qv, $redirect['query']);
                            }
                        }
                    }
                }
            }
        } elseif (is_single() && strpos($wp_rewrite->permalink_structure, '%category%') !== false && $cat = get_query_var('category_name')) {
            $category = get_category_by_path($cat);
            if (!$category || is_wp_error($category) || !has_term($category->term_id, 'category', $wp_query->get_queried_object_id())) {
                $redirect_url = get_permalink($wp_query->get_queried_object_id());
            }
        }
        // Post Paging
        if (is_singular() && get_query_var('page')) {
            if (!$redirect_url) {
                $redirect_url = get_permalink(get_queried_object_id());
            }
            $page = get_query_var('page');
            if ($page > 1) {
                if (is_front_page()) {
                    $redirect_url = trailingslashit($redirect_url) . user_trailingslashit("{$wp_rewrite->pagination_base}/{$page}", 'paged');
                } else {
                    $redirect_url = trailingslashit($redirect_url) . user_trailingslashit($page, 'single_paged');
                }
            }
            $redirect['query'] = remove_query_arg('page', $redirect['query']);
        }
        // paging and feeds
        if (get_query_var('paged') || is_feed() || get_query_var('cpage')) {
            while (preg_match("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", $redirect['path']) || preg_match('#/(comments/?)?(feed|rss|rdf|atom|rss2)(/+)?$#', $redirect['path']) || preg_match("#/{$wp_rewrite->comments_pagination_base}-[0-9]+(/+)?\$#", $redirect['path'])) {
                // Strip off paging and feed
                $redirect['path'] = preg_replace("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", '/', $redirect['path']);
                // strip off any existing paging
                $redirect['path'] = preg_replace('#/(comments/?)?(feed|rss2?|rdf|atom)(/+|$)#', '/', $redirect['path']);
                // strip off feed endings
                $redirect['path'] = preg_replace("#/{$wp_rewrite->comments_pagination_base}-[0-9]+?(/+)?\$#", '/', $redirect['path']);
                // strip off any existing comment paging
            }
            $addl_path = '';
            if (is_feed() && in_array(get_query_var('feed'), $wp_rewrite->feeds)) {
                $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                if (!is_singular() && get_query_var('withcomments')) {
                    $addl_path .= 'comments/';
                }
                if ('rss' == get_default_feed() && 'feed' == get_query_var('feed') || 'rss' == get_query_var('feed')) {
                    $addl_path .= user_trailingslashit('feed/' . ((get_default_feed() == 'rss2') ? '' : 'rss2'), 'feed');
                } else {
                    $addl_path .= user_trailingslashit('feed/' . ((get_default_feed() == get_query_var('feed') || 'feed' == get_query_var('feed')) ? '' : get_query_var('feed')), 'feed');
                }
                $redirect['query'] = remove_query_arg('feed', $redirect['query']);
            } elseif (is_feed() && 'old' == get_query_var('feed')) {
                $old_feed_files = array('wp-atom.php' => 'atom', 'wp-commentsrss2.php' => 'comments_rss2', 'wp-feed.php' => get_default_feed(), 'wp-rdf.php' => 'rdf', 'wp-rss.php' => 'rss2', 'wp-rss2.php' => 'rss2');
                if (isset($old_feed_files[basename($redirect['path'])])) {
                    $redirect_url = get_feed_link($old_feed_files[basename($redirect['path'])]);
                    wp_redirect($redirect_url, 301);
                    die;
                }
            }
            if (get_query_var('paged') > 0) {
                $paged = get_query_var('paged');
                $redirect['query'] = remove_query_arg('paged', $redirect['query']);
                if (!is_feed()) {
                    if ($paged > 1 && !is_single()) {
                        $addl_path = ((!empty($addl_path)) ? trailingslashit($addl_path) : '') . user_trailingslashit("{$wp_rewrite->pagination_base}/{$paged}", 'paged');
                    } elseif (!is_single()) {
                        $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                    }
                } elseif ($paged > 1) {
                    $redirect['query'] = add_query_arg('paged', $paged, $redirect['query']);
                }
            }
            if (get_option('page_comments') && ('newest' == get_option('default_comments_page') && get_query_var('cpage') > 0 || 'newest' != get_option('default_comments_page') && get_query_var('cpage') > 1)) {
                $addl_path = ((!empty($addl_path)) ? trailingslashit($addl_path) : '') . user_trailingslashit($wp_rewrite->comments_pagination_base . '-' . get_query_var('cpage'), 'commentpaged');
                $redirect['query'] = remove_query_arg('cpage', $redirect['query']);
            }
            $redirect['path'] = user_trailingslashit(preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/?$|', '/', $redirect['path']));
            // strip off trailing /index.php/
            if (!empty($addl_path) && $wp_rewrite->using_index_permalinks() && strpos($redirect['path'], '/' . $wp_rewrite->index . '/') === false) {
                $redirect['path'] = trailingslashit($redirect['path']) . $wp_rewrite->index . '/';
            }
            if (!empty($addl_path)) {
                $redirect['path'] = trailingslashit($redirect['path']) . $addl_path;
            }
            $redirect_url = $redirect['scheme'] . '://' . $redirect['host'] . $redirect['path'];
        }
        if ('wp-register.php' == basename($redirect['path'])) {
            if (is_multisite()) {
                /** This filter is documented in wp-login.php */
                $redirect_url = apply_filters('wp_signup_location', network_site_url('wp-signup.php'));
            } else {
                $redirect_url = wp_registration_url();
            }
            wp_redirect($redirect_url, 301);
            die;
        }
    }
    // tack on any additional query vars
    $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    if ($redirect_url && !empty($redirect['query'])) {
        parse_str($redirect['query'], $_parsed_query);
        $redirect = @parse_url($redirect_url);
        if (!empty($_parsed_query['name']) && !empty($redirect['query'])) {
            parse_str($redirect['query'], $_parsed_redirect_query);
            if (empty($_parsed_redirect_query['name'])) {
                unset($_parsed_query['name']);
            }
        }
        $_parsed_query = rawurlencode_deep($_parsed_query);
        $redirect_url = add_query_arg($_parsed_query, $redirect_url);
    }
    if ($redirect_url) {
        $redirect = @parse_url($redirect_url);
    }
    // www.example.com vs example.com
    $user_home = @parse_url(home_url());
    if (!empty($user_home['host'])) {
        $redirect['host'] = $user_home['host'];
    }
    if (empty($user_home['path'])) {
        $user_home['path'] = '/';
    }
    // Handle ports
    if (!empty($user_home['port'])) {
        $redirect['port'] = $user_home['port'];
    } else {
        unset($redirect['port']);
    }
    // trailing /index.php
    $redirect['path'] = preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/*?$|', '/', $redirect['path']);
    $punctuation_pattern = implode('|', array_map('preg_quote', array(
        ' ',
        '%20',
        // space
        '!',
        '%21',
        // exclamation mark
        '"',
        '%22',
        // double quote
        "'",
        '%27',
        // single quote
        '(',
        '%28',
        // opening bracket
        ')',
        '%29',
        // closing bracket
        ',',
        '%2C',
        // comma
        '.',
        '%2E',
        // period
        ';',
        '%3B',
        // semicolon
        '{',
        '%7B',
        // opening curly bracket
        '}',
        '%7D',
        // closing curly bracket
        '%E2%80%9C',
        // opening curly quote
        '%E2%80%9D',
    )));
    // Remove trailing spaces and end punctuation from the path.
    $redirect['path'] = preg_replace("#({$punctuation_pattern})+\$#", '', $redirect['path']);
    if (!empty($redirect['query'])) {
        // Remove trailing spaces and end punctuation from certain terminating query string args.
        $redirect['query'] = preg_replace("#((p|page_id|cat|tag)=[^&]*?)({$punctuation_pattern})+\$#", '$1', $redirect['query']);
        // Clean up empty query strings
        $redirect['query'] = trim(preg_replace('#(^|&)(p|page_id|cat|tag)=?(&|$)#', '&', $redirect['query']), '&');
        // Redirect obsolete feeds
        $redirect['query'] = preg_replace('#(^|&)feed=rss(&|$)#', '$1feed=rss2$2', $redirect['query']);
        // Remove redundant leading ampersands
        $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    }
    // strip /index.php/ when we're not using PATHINFO permalinks
    if (!$wp_rewrite->using_index_permalinks()) {
        $redirect['path'] = str_replace('/' . $wp_rewrite->index . '/', '/', $redirect['path']);
    }
    // trailing slashes
    if (is_object($wp_rewrite) && $wp_rewrite->using_permalinks() && !is_404() && (!is_front_page() || is_front_page() && get_query_var('paged') > 1)) {
        $user_ts_type = '';
        if (get_query_var('paged') > 0) {
            $user_ts_type = 'paged';
        } else {
            foreach (array('single', 'category', 'page', 'day', 'month', 'year', 'home') as $type) {
                $func = 'is_' . $type;
                if (call_user_func($func)) {
                    $user_ts_type = $type;
                    break;
                }
            }
        }
        $redirect['path'] = user_trailingslashit($redirect['path'], $user_ts_type);
    } elseif (is_front_page()) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Strip multiple slashes out of the URL
    if (strpos($redirect['path'], '//') > -1) {
        $redirect['path'] = preg_replace('|/+|', '/', $redirect['path']);
    }
    // Always trailing slash the Front Page URL
    if (trailingslashit($redirect['path']) == trailingslashit($user_home['path'])) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Ignore differences in host capitalization, as this can lead to infinite redirects
    // Only redirect no-www <=> yes-www
    if (strtolower($original['host']) == strtolower($redirect['host']) || strtolower($original['host']) != 'www.' . strtolower($redirect['host']) && 'www.' . strtolower($original['host']) != strtolower($redirect['host'])) {
        $redirect['host'] = $original['host'];
    }
    $compare_original = array($original['host'], $original['path']);
    if (!empty($original['port'])) {
        $compare_original[] = $original['port'];
    }
    if (!empty($original['query'])) {
        $compare_original[] = $original['query'];
    }
    $compare_redirect = array($redirect['host'], $redirect['path']);
    if (!empty($redirect['port'])) {
        $compare_redirect[] = $redirect['port'];
    }
    if (!empty($redirect['query'])) {
        $compare_redirect[] = $redirect['query'];
    }
    if ($compare_original !== $compare_redirect) {
        $redirect_url = $redirect['scheme'] . '://' . $redirect['host'];
        if (!empty($redirect['port'])) {
            $redirect_url .= ':' . $redirect['port'];
        }
        $redirect_url .= $redirect['path'];
        if (!empty($redirect['query'])) {
            $redirect_url .= '?' . $redirect['query'];
        }
    }
    if (!$redirect_url || $redirect_url == $requested_url) {
        return;
    }
    // Hex encoded octets are case-insensitive.
    if (false !== strpos($requested_url, '%')) {
        if (!function_exists('lowercase_octets')) {
            /**
             * Converts the first hex-encoded octet match to lowercase.
             *
             * @since 3.1.0
             * @ignore
             *
             * @param array $matches Hex-encoded octet matches for the requested URL.
             * @return string Lowercased version of the first match.
             */
            function lowercase_octets($matches)
            {
                return strtolower($matches[0]);
            }
        }
        $requested_url = preg_replace_callback('|%[a-fA-F0-9][a-fA-F0-9]|', 'lowercase_octets', $requested_url);
    }
    /**
     * Filters the canonical redirect URL.
     *
     * Returning false to this filter will cancel the redirect.
     *
     * @since 2.3.0
     *
     * @param string $redirect_url  The redirect URL.
     * @param string $requested_url The requested URL.
     */
    $redirect_url = apply_filters('redirect_canonical', $redirect_url, $requested_url);
    // yes, again -- in case the filter aborted the request
    if (!$redirect_url || strip_fragment_from_url($redirect_url) == strip_fragment_from_url($requested_url)) {
        return;
    }
    if ($do_redirect) {
        // protect against chained redirects
        if (!redirect_canonical($redirect_url, false)) {
            wp_redirect($redirect_url, 301);
            exit;
        } else {
            // Debug
            // die("1: $redirect_url<br />2: " . redirect_canonical( $redirect_url, false ) );
            return;
        }
    } else {
        return $redirect_url;
    }
}

WordPress Version: 4.9

/**
 * Canonical API to handle WordPress Redirecting
 *
 * Based on "Permalink Redirect" from Scott Yang and "Enforce www. Preference"
 * by Mark Jaquith
 *
 * @package WordPress
 * @since 2.3.0
 */
/**
 * Redirects incoming links to the proper URL based on the site url.
 *
 * Search engines consider www.somedomain.com and somedomain.com to be two
 * different URLs when they both go to the same location. This SEO enhancement
 * prevents penalty for duplicate content by redirecting all incoming links to
 * one or the other.
 *
 * Prevents redirection for feeds, trackbacks, searches, and
 * admin URLs. Does not redirect on non-pretty-permalink-supporting IIS 7+,
 * page/post previews, WP admin, Trackbacks, robots.txt, searches, or on POST
 * requests.
 *
 * Will also attempt to find the correct link when a user enters a URL that does
 * not exist based on exact WordPress query. Will instead try to parse the URL
 * or query in an attempt to figure the correct page to go to.
 *
 * @since 2.3.0
 *
 * @global WP_Rewrite $wp_rewrite
 * @global bool $is_IIS
 * @global WP_Query $wp_query
 * @global wpdb $wpdb WordPress database abstraction object.
 * @global WP $wp Current WordPress environment instance. 
 *
 * @param string $requested_url Optional. The URL that was requested, used to
 *		figure if redirect is needed.
 * @param bool $do_redirect Optional. Redirect to the new URL.
 * @return string|void The string of the URL, if redirect needed.
 */
function redirect_canonical($requested_url = null, $do_redirect = true)
{
    global $wp_rewrite, $is_IIS, $wp_query, $wpdb, $wp;
    if (isset($_SERVER['REQUEST_METHOD']) && !in_array(strtoupper($_SERVER['REQUEST_METHOD']), array('GET', 'HEAD'))) {
        return;
    }
    // If we're not in wp-admin and the post has been published and preview nonce
    // is non-existent or invalid then no need for preview in query
    if (is_preview() && get_query_var('p') && 'publish' == get_post_status(get_query_var('p'))) {
        if (!isset($_GET['preview_id']) || !isset($_GET['preview_nonce']) || !wp_verify_nonce($_GET['preview_nonce'], 'post_preview_' . (int) $_GET['preview_id'])) {
            $wp_query->is_preview = false;
        }
    }
    if (is_trackback() || is_search() || is_admin() || is_preview() || is_robots() || $is_IIS && !iis7_supports_permalinks()) {
        return;
    }
    if (!$requested_url && isset($_SERVER['HTTP_HOST'])) {
        // build the URL in the address bar
        $requested_url = is_ssl() ? 'https://' : 'http://';
        $requested_url .= $_SERVER['HTTP_HOST'];
        $requested_url .= $_SERVER['REQUEST_URI'];
    }
    $original = @parse_url($requested_url);
    if (false === $original) {
        return;
    }
    $redirect = $original;
    $redirect_url = false;
    // Notice fixing
    if (!isset($redirect['path'])) {
        $redirect['path'] = '';
    }
    if (!isset($redirect['query'])) {
        $redirect['query'] = '';
    }
    // If the original URL ended with non-breaking spaces, they were almost
    // certainly inserted by accident. Let's remove them, so the reader doesn't
    // see a 404 error with no obvious cause.
    $redirect['path'] = preg_replace('|(%C2%A0)+$|i', '', $redirect['path']);
    // It's not a preview, so remove it from URL
    if (get_query_var('preview')) {
        $redirect['query'] = remove_query_arg('preview', $redirect['query']);
    }
    if (is_feed() && $id = get_query_var('p')) {
        if ($redirect_url = get_post_comments_feed_link($id, get_query_var('feed'))) {
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type', 'feed'), $redirect_url);
            $redirect['path'] = parse_url($redirect_url, PHP_URL_PATH);
        }
    }
    if (is_singular() && 1 > $wp_query->post_count && $id = get_query_var('p')) {
        $vars = $wpdb->get_results($wpdb->prepare("SELECT post_type, post_parent FROM {$wpdb->posts} WHERE ID = %d", $id));
        if (isset($vars[0]) && $vars = $vars[0]) {
            if ('revision' == $vars->post_type && $vars->post_parent > 0) {
                $id = $vars->post_parent;
            }
            if ($redirect_url = get_permalink($id)) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    }
    // These tests give us a WP-generated permalink
    if (is_404()) {
        // Redirect ?page_id, ?p=, ?attachment_id= to their respective url's
        $id = max(get_query_var('p'), get_query_var('page_id'), get_query_var('attachment_id'));
        if ($id && $redirect_post = get_post($id)) {
            $post_type_obj = get_post_type_object($redirect_post->post_type);
            if ($post_type_obj->public && 'auto-draft' != $redirect_post->post_status) {
                $redirect_url = get_permalink($redirect_post);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
        if (get_query_var('day') && get_query_var('monthnum') && get_query_var('year')) {
            $year = get_query_var('year');
            $month = get_query_var('monthnum');
            $day = get_query_var('day');
            $date = sprintf('%04d-%02d-%02d', $year, $month, $day);
            if (!wp_checkdate($month, $day, $year, $date)) {
                $redirect_url = get_month_link($year, $month);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum', 'day'), $redirect_url);
            }
        } elseif (get_query_var('monthnum') && get_query_var('year') && 12 < get_query_var('monthnum')) {
            $redirect_url = get_year_link(get_query_var('year'));
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum'), $redirect_url);
        }
        if (!$redirect_url) {
            if ($redirect_url = redirect_guess_404_permalink()) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('page', 'feed', 'p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
        if (get_query_var('page') && $wp_query->post && false !== strpos($wp_query->post->post_content, '<!--nextpage-->')) {
            $redirect['path'] = rtrim($redirect['path'], (int) get_query_var('page') . '/');
            $redirect['query'] = remove_query_arg('page', $redirect['query']);
            $redirect_url = get_permalink($wp_query->post->ID);
        }
    } elseif (is_object($wp_rewrite) && $wp_rewrite->using_permalinks()) {
        // rewriting of old ?p=X, ?m=2004, ?m=200401, ?m=20040101
        if (is_attachment() && !array_diff(array_keys($wp->query_vars), array('attachment', 'attachment_id')) && !$redirect_url) {
            if (!empty($_GET['attachment_id'])) {
                $redirect_url = get_attachment_link(get_query_var('attachment_id'));
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('attachment_id', $redirect['query']);
                }
            } else {
                $redirect_url = get_attachment_link();
            }
        } elseif (is_single() && !empty($_GET['p']) && !$redirect_url) {
            if ($redirect_url = get_permalink(get_query_var('p'))) {
                $redirect['query'] = remove_query_arg(array('p', 'post_type'), $redirect['query']);
            }
        } elseif (is_single() && !empty($_GET['name']) && !$redirect_url) {
            if ($redirect_url = get_permalink($wp_query->get_queried_object_id())) {
                $redirect['query'] = remove_query_arg('name', $redirect['query']);
            }
        } elseif (is_page() && !empty($_GET['page_id']) && !$redirect_url) {
            if ($redirect_url = get_permalink(get_query_var('page_id'))) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (is_page() && !is_feed() && 'page' == get_option('show_on_front') && get_queried_object_id() == get_option('page_on_front') && !$redirect_url) {
            $redirect_url = home_url('/');
        } elseif (is_home() && !empty($_GET['page_id']) && 'page' == get_option('show_on_front') && get_query_var('page_id') == get_option('page_for_posts') && !$redirect_url) {
            if ($redirect_url = get_permalink(get_option('page_for_posts'))) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (!empty($_GET['m']) && (is_year() || is_month() || is_day())) {
            $m = get_query_var('m');
            switch (strlen($m)) {
                case 4:
                    // Yearly
                    $redirect_url = get_year_link($m);
                    break;
                case 6:
                    // Monthly
                    $redirect_url = get_month_link(substr($m, 0, 4), substr($m, 4, 2));
                    break;
                case 8:
                    // Daily
                    $redirect_url = get_day_link(substr($m, 0, 4), substr($m, 4, 2), substr($m, 6, 2));
                    break;
            }
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('m', $redirect['query']);
            }
            // now moving on to non ?m=X year/month/day links
        } elseif (is_day() && get_query_var('year') && get_query_var('monthnum') && !empty($_GET['day'])) {
            if ($redirect_url = get_day_link(get_query_var('year'), get_query_var('monthnum'), get_query_var('day'))) {
                $redirect['query'] = remove_query_arg(array('year', 'monthnum', 'day'), $redirect['query']);
            }
        } elseif (is_month() && get_query_var('year') && !empty($_GET['monthnum'])) {
            if ($redirect_url = get_month_link(get_query_var('year'), get_query_var('monthnum'))) {
                $redirect['query'] = remove_query_arg(array('year', 'monthnum'), $redirect['query']);
            }
        } elseif (is_year() && !empty($_GET['year'])) {
            if ($redirect_url = get_year_link(get_query_var('year'))) {
                $redirect['query'] = remove_query_arg('year', $redirect['query']);
            }
        } elseif (is_author() && !empty($_GET['author']) && preg_match('|^[0-9]+$|', $_GET['author'])) {
            $author = get_userdata(get_query_var('author'));
            if (false !== $author && $wpdb->get_var($wpdb->prepare("SELECT ID FROM {$wpdb->posts} WHERE {$wpdb->posts}.post_author = %d AND {$wpdb->posts}.post_status = 'publish' LIMIT 1", $author->ID))) {
                if ($redirect_url = get_author_posts_url($author->ID, $author->user_nicename)) {
                    $redirect['query'] = remove_query_arg('author', $redirect['query']);
                }
            }
        } elseif (is_category() || is_tag() || is_tax()) {
            // Terms (Tags/categories)
            $term_count = 0;
            foreach ($wp_query->tax_query->queried_terms as $tax_query) {
                $term_count += count($tax_query['terms']);
            }
            $obj = $wp_query->get_queried_object();
            if ($term_count <= 1 && !empty($obj->term_id) && ($tax_url = get_term_link((int) $obj->term_id, $obj->taxonomy)) && !is_wp_error($tax_url)) {
                if (!empty($redirect['query'])) {
                    // Strip taxonomy query vars off the url.
                    $qv_remove = array('term', 'taxonomy');
                    if (is_category()) {
                        $qv_remove[] = 'category_name';
                        $qv_remove[] = 'cat';
                    } elseif (is_tag()) {
                        $qv_remove[] = 'tag';
                        $qv_remove[] = 'tag_id';
                    } else {
                        // Custom taxonomies will have a custom query var, remove those too:
                        $tax_obj = get_taxonomy($obj->taxonomy);
                        if (false !== $tax_obj->query_var) {
                            $qv_remove[] = $tax_obj->query_var;
                        }
                    }
                    $rewrite_vars = array_diff(array_keys($wp_query->query), array_keys($_GET));
                    if (!array_diff($rewrite_vars, array_keys($_GET))) {
                        // Check to see if all the Query vars are coming from the rewrite, none are set via $_GET
                        $redirect['query'] = remove_query_arg($qv_remove, $redirect['query']);
                        //Remove all of the per-tax qv's
                        // Create the destination url for this taxonomy
                        $tax_url = parse_url($tax_url);
                        if (!empty($tax_url['query'])) {
                            // Taxonomy accessible via ?taxonomy=..&term=.. or any custom qv..
                            parse_str($tax_url['query'], $query_vars);
                            $redirect['query'] = add_query_arg($query_vars, $redirect['query']);
                        } else {
                            // Taxonomy is accessible via a "pretty-URL"
                            $redirect['path'] = $tax_url['path'];
                        }
                    } else {
                        // Some query vars are set via $_GET. Unset those from $_GET that exist via the rewrite
                        foreach ($qv_remove as $_qv) {
                            if (isset($rewrite_vars[$_qv])) {
                                $redirect['query'] = remove_query_arg($_qv, $redirect['query']);
                            }
                        }
                    }
                }
            }
        } elseif (is_single() && strpos($wp_rewrite->permalink_structure, '%category%') !== false && $cat = get_query_var('category_name')) {
            $category = get_category_by_path($cat);
            if (!$category || is_wp_error($category) || !has_term($category->term_id, 'category', $wp_query->get_queried_object_id())) {
                $redirect_url = get_permalink($wp_query->get_queried_object_id());
            }
        }
        // Post Paging
        if (is_singular() && get_query_var('page')) {
            if (!$redirect_url) {
                $redirect_url = get_permalink(get_queried_object_id());
            }
            $page = get_query_var('page');
            if ($page > 1) {
                if (is_front_page()) {
                    $redirect_url = trailingslashit($redirect_url) . user_trailingslashit("{$wp_rewrite->pagination_base}/{$page}", 'paged');
                } else {
                    $redirect_url = trailingslashit($redirect_url) . user_trailingslashit($page, 'single_paged');
                }
            }
            $redirect['query'] = remove_query_arg('page', $redirect['query']);
        }
        // paging and feeds
        if (get_query_var('paged') || is_feed() || get_query_var('cpage')) {
            while (preg_match("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", $redirect['path']) || preg_match('#/(comments/?)?(feed|rss|rdf|atom|rss2)(/+)?$#', $redirect['path']) || preg_match("#/{$wp_rewrite->comments_pagination_base}-[0-9]+(/+)?\$#", $redirect['path'])) {
                // Strip off paging and feed
                $redirect['path'] = preg_replace("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", '/', $redirect['path']);
                // strip off any existing paging
                $redirect['path'] = preg_replace('#/(comments/?)?(feed|rss2?|rdf|atom)(/+|$)#', '/', $redirect['path']);
                // strip off feed endings
                $redirect['path'] = preg_replace("#/{$wp_rewrite->comments_pagination_base}-[0-9]+?(/+)?\$#", '/', $redirect['path']);
                // strip off any existing comment paging
            }
            $addl_path = '';
            if (is_feed() && in_array(get_query_var('feed'), $wp_rewrite->feeds)) {
                $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                if (!is_singular() && get_query_var('withcomments')) {
                    $addl_path .= 'comments/';
                }
                if ('rss' == get_default_feed() && 'feed' == get_query_var('feed') || 'rss' == get_query_var('feed')) {
                    $addl_path .= user_trailingslashit('feed/' . ((get_default_feed() == 'rss2') ? '' : 'rss2'), 'feed');
                } else {
                    $addl_path .= user_trailingslashit('feed/' . ((get_default_feed() == get_query_var('feed') || 'feed' == get_query_var('feed')) ? '' : get_query_var('feed')), 'feed');
                }
                $redirect['query'] = remove_query_arg('feed', $redirect['query']);
            } elseif (is_feed() && 'old' == get_query_var('feed')) {
                $old_feed_files = array('wp-atom.php' => 'atom', 'wp-commentsrss2.php' => 'comments_rss2', 'wp-feed.php' => get_default_feed(), 'wp-rdf.php' => 'rdf', 'wp-rss.php' => 'rss2', 'wp-rss2.php' => 'rss2');
                if (isset($old_feed_files[basename($redirect['path'])])) {
                    $redirect_url = get_feed_link($old_feed_files[basename($redirect['path'])]);
                    wp_redirect($redirect_url, 301);
                    die;
                }
            }
            if (get_query_var('paged') > 0) {
                $paged = get_query_var('paged');
                $redirect['query'] = remove_query_arg('paged', $redirect['query']);
                if (!is_feed()) {
                    if ($paged > 1 && !is_single()) {
                        $addl_path = ((!empty($addl_path)) ? trailingslashit($addl_path) : '') . user_trailingslashit("{$wp_rewrite->pagination_base}/{$paged}", 'paged');
                    } elseif (!is_single()) {
                        $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                    }
                } elseif ($paged > 1) {
                    $redirect['query'] = add_query_arg('paged', $paged, $redirect['query']);
                }
            }
            if (get_option('page_comments') && ('newest' == get_option('default_comments_page') && get_query_var('cpage') > 0 || 'newest' != get_option('default_comments_page') && get_query_var('cpage') > 1)) {
                $addl_path = ((!empty($addl_path)) ? trailingslashit($addl_path) : '') . user_trailingslashit($wp_rewrite->comments_pagination_base . '-' . get_query_var('cpage'), 'commentpaged');
                $redirect['query'] = remove_query_arg('cpage', $redirect['query']);
            }
            $redirect['path'] = user_trailingslashit(preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/?$|', '/', $redirect['path']));
            // strip off trailing /index.php/
            if (!empty($addl_path) && $wp_rewrite->using_index_permalinks() && strpos($redirect['path'], '/' . $wp_rewrite->index . '/') === false) {
                $redirect['path'] = trailingslashit($redirect['path']) . $wp_rewrite->index . '/';
            }
            if (!empty($addl_path)) {
                $redirect['path'] = trailingslashit($redirect['path']) . $addl_path;
            }
            $redirect_url = $redirect['scheme'] . '://' . $redirect['host'] . $redirect['path'];
        }
        if ('wp-register.php' == basename($redirect['path'])) {
            if (is_multisite()) {
                /** This filter is documented in wp-login.php */
                $redirect_url = apply_filters('wp_signup_location', network_site_url('wp-signup.php'));
            } else {
                $redirect_url = wp_registration_url();
            }
            wp_redirect($redirect_url, 301);
            die;
        }
    }
    // tack on any additional query vars
    $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    if ($redirect_url && !empty($redirect['query'])) {
        parse_str($redirect['query'], $_parsed_query);
        $redirect = @parse_url($redirect_url);
        if (!empty($_parsed_query['name']) && !empty($redirect['query'])) {
            parse_str($redirect['query'], $_parsed_redirect_query);
            if (empty($_parsed_redirect_query['name'])) {
                unset($_parsed_query['name']);
            }
        }
        $_parsed_query = rawurlencode_deep($_parsed_query);
        $redirect_url = add_query_arg($_parsed_query, $redirect_url);
    }
    if ($redirect_url) {
        $redirect = @parse_url($redirect_url);
    }
    // www.example.com vs example.com
    $user_home = @parse_url(home_url());
    if (!empty($user_home['host'])) {
        $redirect['host'] = $user_home['host'];
    }
    if (empty($user_home['path'])) {
        $user_home['path'] = '/';
    }
    // Handle ports
    if (!empty($user_home['port'])) {
        $redirect['port'] = $user_home['port'];
    } else {
        unset($redirect['port']);
    }
    // trailing /index.php
    $redirect['path'] = preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/*?$|', '/', $redirect['path']);
    $punctuation_pattern = implode('|', array_map('preg_quote', array(
        ' ',
        '%20',
        // space
        '!',
        '%21',
        // exclamation mark
        '"',
        '%22',
        // double quote
        "'",
        '%27',
        // single quote
        '(',
        '%28',
        // opening bracket
        ')',
        '%29',
        // closing bracket
        ',',
        '%2C',
        // comma
        '.',
        '%2E',
        // period
        ';',
        '%3B',
        // semicolon
        '{',
        '%7B',
        // opening curly bracket
        '}',
        '%7D',
        // closing curly bracket
        '%E2%80%9C',
        // opening curly quote
        '%E2%80%9D',
    )));
    // Remove trailing spaces and end punctuation from the path.
    $redirect['path'] = preg_replace("#({$punctuation_pattern})+\$#", '', $redirect['path']);
    if (!empty($redirect['query'])) {
        // Remove trailing spaces and end punctuation from certain terminating query string args.
        $redirect['query'] = preg_replace("#((p|page_id|cat|tag)=[^&]*?)({$punctuation_pattern})+\$#", '$1', $redirect['query']);
        // Clean up empty query strings
        $redirect['query'] = trim(preg_replace('#(^|&)(p|page_id|cat|tag)=?(&|$)#', '&', $redirect['query']), '&');
        // Redirect obsolete feeds
        $redirect['query'] = preg_replace('#(^|&)feed=rss(&|$)#', '$1feed=rss2$2', $redirect['query']);
        // Remove redundant leading ampersands
        $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    }
    // strip /index.php/ when we're not using PATHINFO permalinks
    if (!$wp_rewrite->using_index_permalinks()) {
        $redirect['path'] = str_replace('/' . $wp_rewrite->index . '/', '/', $redirect['path']);
    }
    // trailing slashes
    if (is_object($wp_rewrite) && $wp_rewrite->using_permalinks() && !is_404() && (!is_front_page() || is_front_page() && get_query_var('paged') > 1)) {
        $user_ts_type = '';
        if (get_query_var('paged') > 0) {
            $user_ts_type = 'paged';
        } else {
            foreach (array('single', 'category', 'page', 'day', 'month', 'year', 'home') as $type) {
                $func = 'is_' . $type;
                if (call_user_func($func)) {
                    $user_ts_type = $type;
                    break;
                }
            }
        }
        $redirect['path'] = user_trailingslashit($redirect['path'], $user_ts_type);
    } elseif (is_front_page()) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Strip multiple slashes out of the URL
    if (strpos($redirect['path'], '//') > -1) {
        $redirect['path'] = preg_replace('|/+|', '/', $redirect['path']);
    }
    // Always trailing slash the Front Page URL
    if (trailingslashit($redirect['path']) == trailingslashit($user_home['path'])) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Ignore differences in host capitalization, as this can lead to infinite redirects
    // Only redirect no-www <=> yes-www
    if (strtolower($original['host']) == strtolower($redirect['host']) || strtolower($original['host']) != 'www.' . strtolower($redirect['host']) && 'www.' . strtolower($original['host']) != strtolower($redirect['host'])) {
        $redirect['host'] = $original['host'];
    }
    $compare_original = array($original['host'], $original['path']);
    if (!empty($original['port'])) {
        $compare_original[] = $original['port'];
    }
    if (!empty($original['query'])) {
        $compare_original[] = $original['query'];
    }
    $compare_redirect = array($redirect['host'], $redirect['path']);
    if (!empty($redirect['port'])) {
        $compare_redirect[] = $redirect['port'];
    }
    if (!empty($redirect['query'])) {
        $compare_redirect[] = $redirect['query'];
    }
    if ($compare_original !== $compare_redirect) {
        $redirect_url = $redirect['scheme'] . '://' . $redirect['host'];
        if (!empty($redirect['port'])) {
            $redirect_url .= ':' . $redirect['port'];
        }
        $redirect_url .= $redirect['path'];
        if (!empty($redirect['query'])) {
            $redirect_url .= '?' . $redirect['query'];
        }
    }
    if (!$redirect_url || $redirect_url == $requested_url) {
        return;
    }
    // Hex encoded octets are case-insensitive.
    if (false !== strpos($requested_url, '%')) {
        if (!function_exists('lowercase_octets')) {
            /**
             * Converts the first hex-encoded octet match to lowercase.
             *
             * @since 3.1.0
             * @ignore
             *
             * @param array $matches Hex-encoded octet matches for the requested URL.
             * @return string Lowercased version of the first match.
             */
            function lowercase_octets($matches)
            {
                return strtolower($matches[0]);
            }
        }
        $requested_url = preg_replace_callback('|%[a-fA-F0-9][a-fA-F0-9]|', 'lowercase_octets', $requested_url);
    }
    /**
     * Filters the canonical redirect URL.
     *
     * Returning false to this filter will cancel the redirect.
     *
     * @since 2.3.0
     *
     * @param string $redirect_url  The redirect URL.
     * @param string $requested_url The requested URL.
     */
    $redirect_url = apply_filters('redirect_canonical', $redirect_url, $requested_url);
    // yes, again -- in case the filter aborted the request
    if (!$redirect_url || strip_fragment_from_url($redirect_url) == strip_fragment_from_url($requested_url)) {
        return;
    }
    if ($do_redirect) {
        // protect against chained redirects
        if (!redirect_canonical($redirect_url, false)) {
            wp_redirect($redirect_url, 301);
            exit;
        } else {
            // Debug
            // die("1: $redirect_url<br />2: " . redirect_canonical( $redirect_url, false ) );
            return;
        }
    } else {
        return $redirect_url;
    }
}

WordPress Version: 4.6

/**
 * Canonical API to handle WordPress Redirecting
 *
 * Based on "Permalink Redirect" from Scott Yang and "Enforce www. Preference"
 * by Mark Jaquith
 *
 * @package WordPress
 * @since 2.3.0
 */
/**
 * Redirects incoming links to the proper URL based on the site url.
 *
 * Search engines consider www.somedomain.com and somedomain.com to be two
 * different URLs when they both go to the same location. This SEO enhancement
 * prevents penalty for duplicate content by redirecting all incoming links to
 * one or the other.
 *
 * Prevents redirection for feeds, trackbacks, searches, and
 * admin URLs. Does not redirect on non-pretty-permalink-supporting IIS 7+,
 * page/post previews, WP admin, Trackbacks, robots.txt, searches, or on POST
 * requests.
 *
 * Will also attempt to find the correct link when a user enters a URL that does
 * not exist based on exact WordPress query. Will instead try to parse the URL
 * or query in an attempt to figure the correct page to go to.
 *
 * @since 2.3.0
 *
 * @global WP_Rewrite $wp_rewrite
 * @global bool $is_IIS
 * @global WP_Query $wp_query
 * @global wpdb $wpdb WordPress database abstraction object.
 *
 * @param string $requested_url Optional. The URL that was requested, used to
 *		figure if redirect is needed.
 * @param bool $do_redirect Optional. Redirect to the new URL.
 * @return string|void The string of the URL, if redirect needed.
 */
function redirect_canonical($requested_url = null, $do_redirect = true)
{
    global $wp_rewrite, $is_IIS, $wp_query, $wpdb, $wp;
    if (isset($_SERVER['REQUEST_METHOD']) && !in_array(strtoupper($_SERVER['REQUEST_METHOD']), array('GET', 'HEAD'))) {
        return;
    }
    // If we're not in wp-admin and the post has been published and preview nonce
    // is non-existent or invalid then no need for preview in query
    if (is_preview() && get_query_var('p') && 'publish' == get_post_status(get_query_var('p'))) {
        if (!isset($_GET['preview_id']) || !isset($_GET['preview_nonce']) || !wp_verify_nonce($_GET['preview_nonce'], 'post_preview_' . (int) $_GET['preview_id'])) {
            $wp_query->is_preview = false;
        }
    }
    if (is_trackback() || is_search() || is_admin() || is_preview() || is_robots() || $is_IIS && !iis7_supports_permalinks()) {
        return;
    }
    if (!$requested_url && isset($_SERVER['HTTP_HOST'])) {
        // build the URL in the address bar
        $requested_url = is_ssl() ? 'https://' : 'http://';
        $requested_url .= $_SERVER['HTTP_HOST'];
        $requested_url .= $_SERVER['REQUEST_URI'];
    }
    $original = @parse_url($requested_url);
    if (false === $original) {
        return;
    }
    $redirect = $original;
    $redirect_url = false;
    // Notice fixing
    if (!isset($redirect['path'])) {
        $redirect['path'] = '';
    }
    if (!isset($redirect['query'])) {
        $redirect['query'] = '';
    }
    // If the original URL ended with non-breaking spaces, they were almost
    // certainly inserted by accident. Let's remove them, so the reader doesn't
    // see a 404 error with no obvious cause.
    $redirect['path'] = preg_replace('|(%C2%A0)+$|i', '', $redirect['path']);
    // It's not a preview, so remove it from URL
    if (get_query_var('preview')) {
        $redirect['query'] = remove_query_arg('preview', $redirect['query']);
    }
    if (is_feed() && $id = get_query_var('p')) {
        if ($redirect_url = get_post_comments_feed_link($id, get_query_var('feed'))) {
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type', 'feed'), $redirect_url);
            $redirect['path'] = parse_url($redirect_url, PHP_URL_PATH);
        }
    }
    if (is_singular() && 1 > $wp_query->post_count && $id = get_query_var('p')) {
        $vars = $wpdb->get_results($wpdb->prepare("SELECT post_type, post_parent FROM {$wpdb->posts} WHERE ID = %d", $id));
        if (isset($vars[0]) && $vars = $vars[0]) {
            if ('revision' == $vars->post_type && $vars->post_parent > 0) {
                $id = $vars->post_parent;
            }
            if ($redirect_url = get_permalink($id)) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    }
    // These tests give us a WP-generated permalink
    if (is_404()) {
        // Redirect ?page_id, ?p=, ?attachment_id= to their respective url's
        $id = max(get_query_var('p'), get_query_var('page_id'), get_query_var('attachment_id'));
        if ($id && $redirect_post = get_post($id)) {
            $post_type_obj = get_post_type_object($redirect_post->post_type);
            if ($post_type_obj->public && 'auto-draft' != $redirect_post->post_status) {
                $redirect_url = get_permalink($redirect_post);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
        if (get_query_var('day') && get_query_var('monthnum') && get_query_var('year')) {
            $year = get_query_var('year');
            $month = get_query_var('monthnum');
            $day = get_query_var('day');
            $date = sprintf('%04d-%02d-%02d', $year, $month, $day);
            if (!wp_checkdate($month, $day, $year, $date)) {
                $redirect_url = get_month_link($year, $month);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum', 'day'), $redirect_url);
            }
        } elseif (get_query_var('monthnum') && get_query_var('year') && 12 < get_query_var('monthnum')) {
            $redirect_url = get_year_link(get_query_var('year'));
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum'), $redirect_url);
        }
        if (!$redirect_url) {
            if ($redirect_url = redirect_guess_404_permalink()) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('page', 'feed', 'p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
        if (get_query_var('page') && $wp_query->post && false !== strpos($wp_query->post->post_content, '<!--nextpage-->')) {
            $redirect['path'] = rtrim($redirect['path'], (int) get_query_var('page') . '/');
            $redirect['query'] = remove_query_arg('page', $redirect['query']);
            $redirect_url = get_permalink($wp_query->post->ID);
        }
    } elseif (is_object($wp_rewrite) && $wp_rewrite->using_permalinks()) {
        // rewriting of old ?p=X, ?m=2004, ?m=200401, ?m=20040101
        if (is_attachment() && !array_diff(array_keys($wp->query_vars), array('attachment', 'attachment_id')) && !$redirect_url) {
            if (!empty($_GET['attachment_id'])) {
                $redirect_url = get_attachment_link(get_query_var('attachment_id'));
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('attachment_id', $redirect['query']);
                }
            } else {
                $redirect_url = get_attachment_link();
            }
        } elseif (is_single() && !empty($_GET['p']) && !$redirect_url) {
            if ($redirect_url = get_permalink(get_query_var('p'))) {
                $redirect['query'] = remove_query_arg(array('p', 'post_type'), $redirect['query']);
            }
        } elseif (is_single() && !empty($_GET['name']) && !$redirect_url) {
            if ($redirect_url = get_permalink($wp_query->get_queried_object_id())) {
                $redirect['query'] = remove_query_arg('name', $redirect['query']);
            }
        } elseif (is_page() && !empty($_GET['page_id']) && !$redirect_url) {
            if ($redirect_url = get_permalink(get_query_var('page_id'))) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (is_page() && !is_feed() && 'page' == get_option('show_on_front') && get_queried_object_id() == get_option('page_on_front') && !$redirect_url) {
            $redirect_url = home_url('/');
        } elseif (is_home() && !empty($_GET['page_id']) && 'page' == get_option('show_on_front') && get_query_var('page_id') == get_option('page_for_posts') && !$redirect_url) {
            if ($redirect_url = get_permalink(get_option('page_for_posts'))) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (!empty($_GET['m']) && (is_year() || is_month() || is_day())) {
            $m = get_query_var('m');
            switch (strlen($m)) {
                case 4:
                    // Yearly
                    $redirect_url = get_year_link($m);
                    break;
                case 6:
                    // Monthly
                    $redirect_url = get_month_link(substr($m, 0, 4), substr($m, 4, 2));
                    break;
                case 8:
                    // Daily
                    $redirect_url = get_day_link(substr($m, 0, 4), substr($m, 4, 2), substr($m, 6, 2));
                    break;
            }
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('m', $redirect['query']);
            }
            // now moving on to non ?m=X year/month/day links
        } elseif (is_day() && get_query_var('year') && get_query_var('monthnum') && !empty($_GET['day'])) {
            if ($redirect_url = get_day_link(get_query_var('year'), get_query_var('monthnum'), get_query_var('day'))) {
                $redirect['query'] = remove_query_arg(array('year', 'monthnum', 'day'), $redirect['query']);
            }
        } elseif (is_month() && get_query_var('year') && !empty($_GET['monthnum'])) {
            if ($redirect_url = get_month_link(get_query_var('year'), get_query_var('monthnum'))) {
                $redirect['query'] = remove_query_arg(array('year', 'monthnum'), $redirect['query']);
            }
        } elseif (is_year() && !empty($_GET['year'])) {
            if ($redirect_url = get_year_link(get_query_var('year'))) {
                $redirect['query'] = remove_query_arg('year', $redirect['query']);
            }
        } elseif (is_author() && !empty($_GET['author']) && preg_match('|^[0-9]+$|', $_GET['author'])) {
            $author = get_userdata(get_query_var('author'));
            if (false !== $author && $wpdb->get_var($wpdb->prepare("SELECT ID FROM {$wpdb->posts} WHERE {$wpdb->posts}.post_author = %d AND {$wpdb->posts}.post_status = 'publish' LIMIT 1", $author->ID))) {
                if ($redirect_url = get_author_posts_url($author->ID, $author->user_nicename)) {
                    $redirect['query'] = remove_query_arg('author', $redirect['query']);
                }
            }
        } elseif (is_category() || is_tag() || is_tax()) {
            // Terms (Tags/categories)
            $term_count = 0;
            foreach ($wp_query->tax_query->queried_terms as $tax_query) {
                $term_count += count($tax_query['terms']);
            }
            $obj = $wp_query->get_queried_object();
            if ($term_count <= 1 && !empty($obj->term_id) && ($tax_url = get_term_link((int) $obj->term_id, $obj->taxonomy)) && !is_wp_error($tax_url)) {
                if (!empty($redirect['query'])) {
                    // Strip taxonomy query vars off the url.
                    $qv_remove = array('term', 'taxonomy');
                    if (is_category()) {
                        $qv_remove[] = 'category_name';
                        $qv_remove[] = 'cat';
                    } elseif (is_tag()) {
                        $qv_remove[] = 'tag';
                        $qv_remove[] = 'tag_id';
                    } else {
                        // Custom taxonomies will have a custom query var, remove those too:
                        $tax_obj = get_taxonomy($obj->taxonomy);
                        if (false !== $tax_obj->query_var) {
                            $qv_remove[] = $tax_obj->query_var;
                        }
                    }
                    $rewrite_vars = array_diff(array_keys($wp_query->query), array_keys($_GET));
                    if (!array_diff($rewrite_vars, array_keys($_GET))) {
                        // Check to see if all the Query vars are coming from the rewrite, none are set via $_GET
                        $redirect['query'] = remove_query_arg($qv_remove, $redirect['query']);
                        //Remove all of the per-tax qv's
                        // Create the destination url for this taxonomy
                        $tax_url = parse_url($tax_url);
                        if (!empty($tax_url['query'])) {
                            // Taxonomy accessible via ?taxonomy=..&term=.. or any custom qv..
                            parse_str($tax_url['query'], $query_vars);
                            $redirect['query'] = add_query_arg($query_vars, $redirect['query']);
                        } else {
                            // Taxonomy is accessible via a "pretty-URL"
                            $redirect['path'] = $tax_url['path'];
                        }
                    } else {
                        // Some query vars are set via $_GET. Unset those from $_GET that exist via the rewrite
                        foreach ($qv_remove as $_qv) {
                            if (isset($rewrite_vars[$_qv])) {
                                $redirect['query'] = remove_query_arg($_qv, $redirect['query']);
                            }
                        }
                    }
                }
            }
        } elseif (is_single() && strpos($wp_rewrite->permalink_structure, '%category%') !== false && $cat = get_query_var('category_name')) {
            $category = get_category_by_path($cat);
            if (!$category || is_wp_error($category) || !has_term($category->term_id, 'category', $wp_query->get_queried_object_id())) {
                $redirect_url = get_permalink($wp_query->get_queried_object_id());
            }
        }
        // Post Paging
        if (is_singular() && get_query_var('page')) {
            if (!$redirect_url) {
                $redirect_url = get_permalink(get_queried_object_id());
            }
            $page = get_query_var('page');
            if ($page > 1) {
                if (is_front_page()) {
                    $redirect_url = trailingslashit($redirect_url) . user_trailingslashit("{$wp_rewrite->pagination_base}/{$page}", 'paged');
                } else {
                    $redirect_url = trailingslashit($redirect_url) . user_trailingslashit($page, 'single_paged');
                }
            }
            $redirect['query'] = remove_query_arg('page', $redirect['query']);
        }
        // paging and feeds
        if (get_query_var('paged') || is_feed() || get_query_var('cpage')) {
            while (preg_match("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", $redirect['path']) || preg_match('#/(comments/?)?(feed|rss|rdf|atom|rss2)(/+)?$#', $redirect['path']) || preg_match("#/{$wp_rewrite->comments_pagination_base}-[0-9]+(/+)?\$#", $redirect['path'])) {
                // Strip off paging and feed
                $redirect['path'] = preg_replace("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", '/', $redirect['path']);
                // strip off any existing paging
                $redirect['path'] = preg_replace('#/(comments/?)?(feed|rss2?|rdf|atom)(/+|$)#', '/', $redirect['path']);
                // strip off feed endings
                $redirect['path'] = preg_replace("#/{$wp_rewrite->comments_pagination_base}-[0-9]+?(/+)?\$#", '/', $redirect['path']);
                // strip off any existing comment paging
            }
            $addl_path = '';
            if (is_feed() && in_array(get_query_var('feed'), $wp_rewrite->feeds)) {
                $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                if (!is_singular() && get_query_var('withcomments')) {
                    $addl_path .= 'comments/';
                }
                if ('rss' == get_default_feed() && 'feed' == get_query_var('feed') || 'rss' == get_query_var('feed')) {
                    $addl_path .= user_trailingslashit('feed/' . ((get_default_feed() == 'rss2') ? '' : 'rss2'), 'feed');
                } else {
                    $addl_path .= user_trailingslashit('feed/' . ((get_default_feed() == get_query_var('feed') || 'feed' == get_query_var('feed')) ? '' : get_query_var('feed')), 'feed');
                }
                $redirect['query'] = remove_query_arg('feed', $redirect['query']);
            } elseif (is_feed() && 'old' == get_query_var('feed')) {
                $old_feed_files = array('wp-atom.php' => 'atom', 'wp-commentsrss2.php' => 'comments_rss2', 'wp-feed.php' => get_default_feed(), 'wp-rdf.php' => 'rdf', 'wp-rss.php' => 'rss2', 'wp-rss2.php' => 'rss2');
                if (isset($old_feed_files[basename($redirect['path'])])) {
                    $redirect_url = get_feed_link($old_feed_files[basename($redirect['path'])]);
                    wp_redirect($redirect_url, 301);
                    die;
                }
            }
            if (get_query_var('paged') > 0) {
                $paged = get_query_var('paged');
                $redirect['query'] = remove_query_arg('paged', $redirect['query']);
                if (!is_feed()) {
                    if ($paged > 1 && !is_single()) {
                        $addl_path = ((!empty($addl_path)) ? trailingslashit($addl_path) : '') . user_trailingslashit("{$wp_rewrite->pagination_base}/{$paged}", 'paged');
                    } elseif (!is_single()) {
                        $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                    }
                } elseif ($paged > 1) {
                    $redirect['query'] = add_query_arg('paged', $paged, $redirect['query']);
                }
            }
            if (get_option('page_comments') && ('newest' == get_option('default_comments_page') && get_query_var('cpage') > 0 || 'newest' != get_option('default_comments_page') && get_query_var('cpage') > 1)) {
                $addl_path = ((!empty($addl_path)) ? trailingslashit($addl_path) : '') . user_trailingslashit($wp_rewrite->comments_pagination_base . '-' . get_query_var('cpage'), 'commentpaged');
                $redirect['query'] = remove_query_arg('cpage', $redirect['query']);
            }
            $redirect['path'] = user_trailingslashit(preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/?$|', '/', $redirect['path']));
            // strip off trailing /index.php/
            if (!empty($addl_path) && $wp_rewrite->using_index_permalinks() && strpos($redirect['path'], '/' . $wp_rewrite->index . '/') === false) {
                $redirect['path'] = trailingslashit($redirect['path']) . $wp_rewrite->index . '/';
            }
            if (!empty($addl_path)) {
                $redirect['path'] = trailingslashit($redirect['path']) . $addl_path;
            }
            $redirect_url = $redirect['scheme'] . '://' . $redirect['host'] . $redirect['path'];
        }
        if ('wp-register.php' == basename($redirect['path'])) {
            if (is_multisite()) {
                /** This filter is documented in wp-login.php */
                $redirect_url = apply_filters('wp_signup_location', network_site_url('wp-signup.php'));
            } else {
                $redirect_url = wp_registration_url();
            }
            wp_redirect($redirect_url, 301);
            die;
        }
    }
    // tack on any additional query vars
    $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    if ($redirect_url && !empty($redirect['query'])) {
        parse_str($redirect['query'], $_parsed_query);
        $redirect = @parse_url($redirect_url);
        if (!empty($_parsed_query['name']) && !empty($redirect['query'])) {
            parse_str($redirect['query'], $_parsed_redirect_query);
            if (empty($_parsed_redirect_query['name'])) {
                unset($_parsed_query['name']);
            }
        }
        $_parsed_query = rawurlencode_deep($_parsed_query);
        $redirect_url = add_query_arg($_parsed_query, $redirect_url);
    }
    if ($redirect_url) {
        $redirect = @parse_url($redirect_url);
    }
    // www.example.com vs example.com
    $user_home = @parse_url(home_url());
    if (!empty($user_home['host'])) {
        $redirect['host'] = $user_home['host'];
    }
    if (empty($user_home['path'])) {
        $user_home['path'] = '/';
    }
    // Handle ports
    if (!empty($user_home['port'])) {
        $redirect['port'] = $user_home['port'];
    } else {
        unset($redirect['port']);
    }
    // trailing /index.php
    $redirect['path'] = preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/*?$|', '/', $redirect['path']);
    // Remove trailing spaces from the path
    $redirect['path'] = preg_replace('#(%20| )+$#', '', $redirect['path']);
    if (!empty($redirect['query'])) {
        // Remove trailing spaces from certain terminating query string args
        $redirect['query'] = preg_replace('#((p|page_id|cat|tag)=[^&]*?)(%20| )+$#', '$1', $redirect['query']);
        // Clean up empty query strings
        $redirect['query'] = trim(preg_replace('#(^|&)(p|page_id|cat|tag)=?(&|$)#', '&', $redirect['query']), '&');
        // Redirect obsolete feeds
        $redirect['query'] = preg_replace('#(^|&)feed=rss(&|$)#', '$1feed=rss2$2', $redirect['query']);
        // Remove redundant leading ampersands
        $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    }
    // strip /index.php/ when we're not using PATHINFO permalinks
    if (!$wp_rewrite->using_index_permalinks()) {
        $redirect['path'] = str_replace('/' . $wp_rewrite->index . '/', '/', $redirect['path']);
    }
    // trailing slashes
    if (is_object($wp_rewrite) && $wp_rewrite->using_permalinks() && !is_404() && (!is_front_page() || is_front_page() && get_query_var('paged') > 1)) {
        $user_ts_type = '';
        if (get_query_var('paged') > 0) {
            $user_ts_type = 'paged';
        } else {
            foreach (array('single', 'category', 'page', 'day', 'month', 'year', 'home') as $type) {
                $func = 'is_' . $type;
                if (call_user_func($func)) {
                    $user_ts_type = $type;
                    break;
                }
            }
        }
        $redirect['path'] = user_trailingslashit($redirect['path'], $user_ts_type);
    } elseif (is_front_page()) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Strip multiple slashes out of the URL
    if (strpos($redirect['path'], '//') > -1) {
        $redirect['path'] = preg_replace('|/+|', '/', $redirect['path']);
    }
    // Always trailing slash the Front Page URL
    if (trailingslashit($redirect['path']) == trailingslashit($user_home['path'])) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Ignore differences in host capitalization, as this can lead to infinite redirects
    // Only redirect no-www <=> yes-www
    if (strtolower($original['host']) == strtolower($redirect['host']) || strtolower($original['host']) != 'www.' . strtolower($redirect['host']) && 'www.' . strtolower($original['host']) != strtolower($redirect['host'])) {
        $redirect['host'] = $original['host'];
    }
    $compare_original = array($original['host'], $original['path']);
    if (!empty($original['port'])) {
        $compare_original[] = $original['port'];
    }
    if (!empty($original['query'])) {
        $compare_original[] = $original['query'];
    }
    $compare_redirect = array($redirect['host'], $redirect['path']);
    if (!empty($redirect['port'])) {
        $compare_redirect[] = $redirect['port'];
    }
    if (!empty($redirect['query'])) {
        $compare_redirect[] = $redirect['query'];
    }
    if ($compare_original !== $compare_redirect) {
        $redirect_url = $redirect['scheme'] . '://' . $redirect['host'];
        if (!empty($redirect['port'])) {
            $redirect_url .= ':' . $redirect['port'];
        }
        $redirect_url .= $redirect['path'];
        if (!empty($redirect['query'])) {
            $redirect_url .= '?' . $redirect['query'];
        }
    }
    if (!$redirect_url || $redirect_url == $requested_url) {
        return;
    }
    // Hex encoded octets are case-insensitive.
    if (false !== strpos($requested_url, '%')) {
        if (!function_exists('lowercase_octets')) {
            /**
             * Converts the first hex-encoded octet match to lowercase.
             *
             * @since 3.1.0
             * @ignore
             *
             * @param array $matches Hex-encoded octet matches for the requested URL.
             * @return string Lowercased version of the first match.
             */
            function lowercase_octets($matches)
            {
                return strtolower($matches[0]);
            }
        }
        $requested_url = preg_replace_callback('|%[a-fA-F0-9][a-fA-F0-9]|', 'lowercase_octets', $requested_url);
    }
    /**
     * Filters the canonical redirect URL.
     *
     * Returning false to this filter will cancel the redirect.
     *
     * @since 2.3.0
     *
     * @param string $redirect_url  The redirect URL.
     * @param string $requested_url The requested URL.
     */
    $redirect_url = apply_filters('redirect_canonical', $redirect_url, $requested_url);
    // yes, again -- in case the filter aborted the request
    if (!$redirect_url || strip_fragment_from_url($redirect_url) == strip_fragment_from_url($requested_url)) {
        return;
    }
    if ($do_redirect) {
        // protect against chained redirects
        if (!redirect_canonical($redirect_url, false)) {
            wp_redirect($redirect_url, 301);
            exit;
        } else {
            // Debug
            // die("1: $redirect_url<br />2: " . redirect_canonical( $redirect_url, false ) );
            return;
        }
    } else {
        return $redirect_url;
    }
}

WordPress Version: 4.5

/**
 * Canonical API to handle WordPress Redirecting
 *
 * Based on "Permalink Redirect" from Scott Yang and "Enforce www. Preference"
 * by Mark Jaquith
 *
 * @package WordPress
 * @since 2.3.0
 */
/**
 * Redirects incoming links to the proper URL based on the site url.
 *
 * Search engines consider www.somedomain.com and somedomain.com to be two
 * different URLs when they both go to the same location. This SEO enhancement
 * prevents penalty for duplicate content by redirecting all incoming links to
 * one or the other.
 *
 * Prevents redirection for feeds, trackbacks, searches, and
 * admin URLs. Does not redirect on non-pretty-permalink-supporting IIS 7+,
 * page/post previews, WP admin, Trackbacks, robots.txt, searches, or on POST
 * requests.
 *
 * Will also attempt to find the correct link when a user enters a URL that does
 * not exist based on exact WordPress query. Will instead try to parse the URL
 * or query in an attempt to figure the correct page to go to.
 *
 * @since 2.3.0
 *
 * @global WP_Rewrite $wp_rewrite
 * @global bool $is_IIS
 * @global WP_Query $wp_query
 * @global wpdb $wpdb WordPress database abstraction object.
 *
 * @param string $requested_url Optional. The URL that was requested, used to
 *		figure if redirect is needed.
 * @param bool $do_redirect Optional. Redirect to the new URL.
 * @return string|void The string of the URL, if redirect needed.
 */
function redirect_canonical($requested_url = null, $do_redirect = true)
{
    global $wp_rewrite, $is_IIS, $wp_query, $wpdb, $wp;
    if (isset($_SERVER['REQUEST_METHOD']) && !in_array(strtoupper($_SERVER['REQUEST_METHOD']), array('GET', 'HEAD'))) {
        return;
    }
    // If we're not in wp-admin and the post has been published and preview nonce
    // is non-existent or invalid then no need for preview in query
    if (is_preview() && get_query_var('p') && 'publish' == get_post_status(get_query_var('p'))) {
        if (!isset($_GET['preview_id']) || !isset($_GET['preview_nonce']) || !wp_verify_nonce($_GET['preview_nonce'], 'post_preview_' . (int) $_GET['preview_id'])) {
            $wp_query->is_preview = false;
        }
    }
    if (is_trackback() || is_search() || is_admin() || is_preview() || is_robots() || $is_IIS && !iis7_supports_permalinks()) {
        return;
    }
    if (!$requested_url && isset($_SERVER['HTTP_HOST'])) {
        // build the URL in the address bar
        $requested_url = is_ssl() ? 'https://' : 'http://';
        $requested_url .= $_SERVER['HTTP_HOST'];
        $requested_url .= $_SERVER['REQUEST_URI'];
    }
    $original = @parse_url($requested_url);
    if (false === $original) {
        return;
    }
    $redirect = $original;
    $redirect_url = false;
    // Notice fixing
    if (!isset($redirect['path'])) {
        $redirect['path'] = '';
    }
    if (!isset($redirect['query'])) {
        $redirect['query'] = '';
    }
    // If the original URL ended with non-breaking spaces, they were almost
    // certainly inserted by accident. Let's remove them, so the reader doesn't
    // see a 404 error with no obvious cause.
    $redirect['path'] = preg_replace('|(%C2%A0)+$|i', '', $redirect['path']);
    // It's not a preview, so remove it from URL
    if (get_query_var('preview')) {
        $redirect['query'] = remove_query_arg('preview', $redirect['query']);
    }
    if (is_feed() && $id = get_query_var('p')) {
        if ($redirect_url = get_post_comments_feed_link($id, get_query_var('feed'))) {
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type', 'feed'), $redirect_url);
            $redirect['path'] = parse_url($redirect_url, PHP_URL_PATH);
        }
    }
    if (is_singular() && 1 > $wp_query->post_count && $id = get_query_var('p')) {
        $vars = $wpdb->get_results($wpdb->prepare("SELECT post_type, post_parent FROM {$wpdb->posts} WHERE ID = %d", $id));
        if (isset($vars[0]) && $vars = $vars[0]) {
            if ('revision' == $vars->post_type && $vars->post_parent > 0) {
                $id = $vars->post_parent;
            }
            if ($redirect_url = get_permalink($id)) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    }
    // These tests give us a WP-generated permalink
    if (is_404()) {
        // Redirect ?page_id, ?p=, ?attachment_id= to their respective url's
        $id = max(get_query_var('p'), get_query_var('page_id'), get_query_var('attachment_id'));
        if ($id && $redirect_post = get_post($id)) {
            $post_type_obj = get_post_type_object($redirect_post->post_type);
            if ($post_type_obj->public && 'auto-draft' != $redirect_post->post_status) {
                $redirect_url = get_permalink($redirect_post);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
        if (get_query_var('day') && get_query_var('monthnum') && get_query_var('year')) {
            $year = get_query_var('year');
            $month = get_query_var('monthnum');
            $day = get_query_var('day');
            $date = sprintf('%04d-%02d-%02d', $year, $month, $day);
            if (!wp_checkdate($month, $day, $year, $date)) {
                $redirect_url = get_month_link($year, $month);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum', 'day'), $redirect_url);
            }
        } elseif (get_query_var('monthnum') && get_query_var('year') && 12 < get_query_var('monthnum')) {
            $redirect_url = get_year_link(get_query_var('year'));
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum'), $redirect_url);
        }
        if (!$redirect_url) {
            if ($redirect_url = redirect_guess_404_permalink()) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('page', 'feed', 'p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
        if (get_query_var('page') && $wp_query->post && false !== strpos($wp_query->post->post_content, '<!--nextpage-->')) {
            $redirect['path'] = rtrim($redirect['path'], (int) get_query_var('page') . '/');
            $redirect['query'] = remove_query_arg('page', $redirect['query']);
            $redirect_url = get_permalink($wp_query->post->ID);
        }
    } elseif (is_object($wp_rewrite) && $wp_rewrite->using_permalinks()) {
        // rewriting of old ?p=X, ?m=2004, ?m=200401, ?m=20040101
        if (is_attachment() && !array_diff(array_keys($wp->query_vars), array('attachment', 'attachment_id')) && !$redirect_url) {
            if (!empty($_GET['attachment_id'])) {
                $redirect_url = get_attachment_link(get_query_var('attachment_id'));
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('attachment_id', $redirect['query']);
                }
            } else {
                $redirect_url = get_attachment_link();
            }
        } elseif (is_single() && !empty($_GET['p']) && !$redirect_url) {
            if ($redirect_url = get_permalink(get_query_var('p'))) {
                $redirect['query'] = remove_query_arg(array('p', 'post_type'), $redirect['query']);
            }
        } elseif (is_single() && !empty($_GET['name']) && !$redirect_url) {
            if ($redirect_url = get_permalink($wp_query->get_queried_object_id())) {
                $redirect['query'] = remove_query_arg('name', $redirect['query']);
            }
        } elseif (is_page() && !empty($_GET['page_id']) && !$redirect_url) {
            if ($redirect_url = get_permalink(get_query_var('page_id'))) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (is_page() && !is_feed() && 'page' == get_option('show_on_front') && get_queried_object_id() == get_option('page_on_front') && !$redirect_url) {
            $redirect_url = home_url('/');
        } elseif (is_home() && !empty($_GET['page_id']) && 'page' == get_option('show_on_front') && get_query_var('page_id') == get_option('page_for_posts') && !$redirect_url) {
            if ($redirect_url = get_permalink(get_option('page_for_posts'))) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (!empty($_GET['m']) && (is_year() || is_month() || is_day())) {
            $m = get_query_var('m');
            switch (strlen($m)) {
                case 4:
                    // Yearly
                    $redirect_url = get_year_link($m);
                    break;
                case 6:
                    // Monthly
                    $redirect_url = get_month_link(substr($m, 0, 4), substr($m, 4, 2));
                    break;
                case 8:
                    // Daily
                    $redirect_url = get_day_link(substr($m, 0, 4), substr($m, 4, 2), substr($m, 6, 2));
                    break;
            }
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('m', $redirect['query']);
            }
            // now moving on to non ?m=X year/month/day links
        } elseif (is_day() && get_query_var('year') && get_query_var('monthnum') && !empty($_GET['day'])) {
            if ($redirect_url = get_day_link(get_query_var('year'), get_query_var('monthnum'), get_query_var('day'))) {
                $redirect['query'] = remove_query_arg(array('year', 'monthnum', 'day'), $redirect['query']);
            }
        } elseif (is_month() && get_query_var('year') && !empty($_GET['monthnum'])) {
            if ($redirect_url = get_month_link(get_query_var('year'), get_query_var('monthnum'))) {
                $redirect['query'] = remove_query_arg(array('year', 'monthnum'), $redirect['query']);
            }
        } elseif (is_year() && !empty($_GET['year'])) {
            if ($redirect_url = get_year_link(get_query_var('year'))) {
                $redirect['query'] = remove_query_arg('year', $redirect['query']);
            }
        } elseif (is_author() && !empty($_GET['author']) && preg_match('|^[0-9]+$|', $_GET['author'])) {
            $author = get_userdata(get_query_var('author'));
            if (false !== $author && $wpdb->get_var($wpdb->prepare("SELECT ID FROM {$wpdb->posts} WHERE {$wpdb->posts}.post_author = %d AND {$wpdb->posts}.post_status = 'publish' LIMIT 1", $author->ID))) {
                if ($redirect_url = get_author_posts_url($author->ID, $author->user_nicename)) {
                    $redirect['query'] = remove_query_arg('author', $redirect['query']);
                }
            }
        } elseif (is_category() || is_tag() || is_tax()) {
            // Terms (Tags/categories)
            $term_count = 0;
            foreach ($wp_query->tax_query->queried_terms as $tax_query) {
                $term_count += count($tax_query['terms']);
            }
            $obj = $wp_query->get_queried_object();
            if ($term_count <= 1 && !empty($obj->term_id) && ($tax_url = get_term_link((int) $obj->term_id, $obj->taxonomy)) && !is_wp_error($tax_url)) {
                if (!empty($redirect['query'])) {
                    // Strip taxonomy query vars off the url.
                    $qv_remove = array('term', 'taxonomy');
                    if (is_category()) {
                        $qv_remove[] = 'category_name';
                        $qv_remove[] = 'cat';
                    } elseif (is_tag()) {
                        $qv_remove[] = 'tag';
                        $qv_remove[] = 'tag_id';
                    } else {
                        // Custom taxonomies will have a custom query var, remove those too:
                        $tax_obj = get_taxonomy($obj->taxonomy);
                        if (false !== $tax_obj->query_var) {
                            $qv_remove[] = $tax_obj->query_var;
                        }
                    }
                    $rewrite_vars = array_diff(array_keys($wp_query->query), array_keys($_GET));
                    if (!array_diff($rewrite_vars, array_keys($_GET))) {
                        // Check to see if all the Query vars are coming from the rewrite, none are set via $_GET
                        $redirect['query'] = remove_query_arg($qv_remove, $redirect['query']);
                        //Remove all of the per-tax qv's
                        // Create the destination url for this taxonomy
                        $tax_url = parse_url($tax_url);
                        if (!empty($tax_url['query'])) {
                            // Taxonomy accessible via ?taxonomy=..&term=.. or any custom qv..
                            parse_str($tax_url['query'], $query_vars);
                            $redirect['query'] = add_query_arg($query_vars, $redirect['query']);
                        } else {
                            // Taxonomy is accessible via a "pretty-URL"
                            $redirect['path'] = $tax_url['path'];
                        }
                    } else {
                        // Some query vars are set via $_GET. Unset those from $_GET that exist via the rewrite
                        foreach ($qv_remove as $_qv) {
                            if (isset($rewrite_vars[$_qv])) {
                                $redirect['query'] = remove_query_arg($_qv, $redirect['query']);
                            }
                        }
                    }
                }
            }
        } elseif (is_single() && strpos($wp_rewrite->permalink_structure, '%category%') !== false && $cat = get_query_var('category_name')) {
            $category = get_category_by_path($cat);
            $post_terms = wp_get_object_terms($wp_query->get_queried_object_id(), 'category', array('fields' => 'tt_ids'));
            if (!$category || is_wp_error($category) || !is_wp_error($post_terms) && !empty($post_terms) && !in_array($category->term_taxonomy_id, $post_terms)) {
                $redirect_url = get_permalink($wp_query->get_queried_object_id());
            }
        }
        // Post Paging
        if (is_singular() && get_query_var('page')) {
            if (!$redirect_url) {
                $redirect_url = get_permalink(get_queried_object_id());
            }
            $page = get_query_var('page');
            if ($page > 1) {
                if (is_front_page()) {
                    $redirect_url = trailingslashit($redirect_url) . user_trailingslashit("{$wp_rewrite->pagination_base}/{$page}", 'paged');
                } else {
                    $redirect_url = trailingslashit($redirect_url) . user_trailingslashit($page, 'single_paged');
                }
            }
            $redirect['query'] = remove_query_arg('page', $redirect['query']);
        }
        // paging and feeds
        if (get_query_var('paged') || is_feed() || get_query_var('cpage')) {
            while (preg_match("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", $redirect['path']) || preg_match('#/(comments/?)?(feed|rss|rdf|atom|rss2)(/+)?$#', $redirect['path']) || preg_match("#/{$wp_rewrite->comments_pagination_base}-[0-9]+(/+)?\$#", $redirect['path'])) {
                // Strip off paging and feed
                $redirect['path'] = preg_replace("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", '/', $redirect['path']);
                // strip off any existing paging
                $redirect['path'] = preg_replace('#/(comments/?)?(feed|rss2?|rdf|atom)(/+|$)#', '/', $redirect['path']);
                // strip off feed endings
                $redirect['path'] = preg_replace("#/{$wp_rewrite->comments_pagination_base}-[0-9]+?(/+)?\$#", '/', $redirect['path']);
                // strip off any existing comment paging
            }
            $addl_path = '';
            if (is_feed() && in_array(get_query_var('feed'), $wp_rewrite->feeds)) {
                $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                if (!is_singular() && get_query_var('withcomments')) {
                    $addl_path .= 'comments/';
                }
                if ('rss' == get_default_feed() && 'feed' == get_query_var('feed') || 'rss' == get_query_var('feed')) {
                    $addl_path .= user_trailingslashit('feed/' . ((get_default_feed() == 'rss2') ? '' : 'rss2'), 'feed');
                } else {
                    $addl_path .= user_trailingslashit('feed/' . ((get_default_feed() == get_query_var('feed') || 'feed' == get_query_var('feed')) ? '' : get_query_var('feed')), 'feed');
                }
                $redirect['query'] = remove_query_arg('feed', $redirect['query']);
            } elseif (is_feed() && 'old' == get_query_var('feed')) {
                $old_feed_files = array('wp-atom.php' => 'atom', 'wp-commentsrss2.php' => 'comments_rss2', 'wp-feed.php' => get_default_feed(), 'wp-rdf.php' => 'rdf', 'wp-rss.php' => 'rss2', 'wp-rss2.php' => 'rss2');
                if (isset($old_feed_files[basename($redirect['path'])])) {
                    $redirect_url = get_feed_link($old_feed_files[basename($redirect['path'])]);
                    wp_redirect($redirect_url, 301);
                    die;
                }
            }
            if (get_query_var('paged') > 0) {
                $paged = get_query_var('paged');
                $redirect['query'] = remove_query_arg('paged', $redirect['query']);
                if (!is_feed()) {
                    if ($paged > 1 && !is_single()) {
                        $addl_path = ((!empty($addl_path)) ? trailingslashit($addl_path) : '') . user_trailingslashit("{$wp_rewrite->pagination_base}/{$paged}", 'paged');
                    } elseif (!is_single()) {
                        $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                    }
                } elseif ($paged > 1) {
                    $redirect['query'] = add_query_arg('paged', $paged, $redirect['query']);
                }
            }
            if (get_option('page_comments') && ('newest' == get_option('default_comments_page') && get_query_var('cpage') > 0 || 'newest' != get_option('default_comments_page') && get_query_var('cpage') > 1)) {
                $addl_path = ((!empty($addl_path)) ? trailingslashit($addl_path) : '') . user_trailingslashit($wp_rewrite->comments_pagination_base . '-' . get_query_var('cpage'), 'commentpaged');
                $redirect['query'] = remove_query_arg('cpage', $redirect['query']);
            }
            $redirect['path'] = user_trailingslashit(preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/?$|', '/', $redirect['path']));
            // strip off trailing /index.php/
            if (!empty($addl_path) && $wp_rewrite->using_index_permalinks() && strpos($redirect['path'], '/' . $wp_rewrite->index . '/') === false) {
                $redirect['path'] = trailingslashit($redirect['path']) . $wp_rewrite->index . '/';
            }
            if (!empty($addl_path)) {
                $redirect['path'] = trailingslashit($redirect['path']) . $addl_path;
            }
            $redirect_url = $redirect['scheme'] . '://' . $redirect['host'] . $redirect['path'];
        }
        if ('wp-register.php' == basename($redirect['path'])) {
            if (is_multisite()) {
                /** This filter is documented in wp-login.php */
                $redirect_url = apply_filters('wp_signup_location', network_site_url('wp-signup.php'));
            } else {
                $redirect_url = wp_registration_url();
            }
            wp_redirect($redirect_url, 301);
            die;
        }
    }
    // tack on any additional query vars
    $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    if ($redirect_url && !empty($redirect['query'])) {
        parse_str($redirect['query'], $_parsed_query);
        $redirect = @parse_url($redirect_url);
        if (!empty($_parsed_query['name']) && !empty($redirect['query'])) {
            parse_str($redirect['query'], $_parsed_redirect_query);
            if (empty($_parsed_redirect_query['name'])) {
                unset($_parsed_query['name']);
            }
        }
        $_parsed_query = rawurlencode_deep($_parsed_query);
        $redirect_url = add_query_arg($_parsed_query, $redirect_url);
    }
    if ($redirect_url) {
        $redirect = @parse_url($redirect_url);
    }
    // www.example.com vs example.com
    $user_home = @parse_url(home_url());
    if (!empty($user_home['host'])) {
        $redirect['host'] = $user_home['host'];
    }
    if (empty($user_home['path'])) {
        $user_home['path'] = '/';
    }
    // Handle ports
    if (!empty($user_home['port'])) {
        $redirect['port'] = $user_home['port'];
    } else {
        unset($redirect['port']);
    }
    // trailing /index.php
    $redirect['path'] = preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/*?$|', '/', $redirect['path']);
    // Remove trailing spaces from the path
    $redirect['path'] = preg_replace('#(%20| )+$#', '', $redirect['path']);
    if (!empty($redirect['query'])) {
        // Remove trailing spaces from certain terminating query string args
        $redirect['query'] = preg_replace('#((p|page_id|cat|tag)=[^&]*?)(%20| )+$#', '$1', $redirect['query']);
        // Clean up empty query strings
        $redirect['query'] = trim(preg_replace('#(^|&)(p|page_id|cat|tag)=?(&|$)#', '&', $redirect['query']), '&');
        // Redirect obsolete feeds
        $redirect['query'] = preg_replace('#(^|&)feed=rss(&|$)#', '$1feed=rss2$2', $redirect['query']);
        // Remove redundant leading ampersands
        $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    }
    // strip /index.php/ when we're not using PATHINFO permalinks
    if (!$wp_rewrite->using_index_permalinks()) {
        $redirect['path'] = str_replace('/' . $wp_rewrite->index . '/', '/', $redirect['path']);
    }
    // trailing slashes
    if (is_object($wp_rewrite) && $wp_rewrite->using_permalinks() && !is_404() && (!is_front_page() || is_front_page() && get_query_var('paged') > 1)) {
        $user_ts_type = '';
        if (get_query_var('paged') > 0) {
            $user_ts_type = 'paged';
        } else {
            foreach (array('single', 'category', 'page', 'day', 'month', 'year', 'home') as $type) {
                $func = 'is_' . $type;
                if (call_user_func($func)) {
                    $user_ts_type = $type;
                    break;
                }
            }
        }
        $redirect['path'] = user_trailingslashit($redirect['path'], $user_ts_type);
    } elseif (is_front_page()) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Strip multiple slashes out of the URL
    if (strpos($redirect['path'], '//') > -1) {
        $redirect['path'] = preg_replace('|/+|', '/', $redirect['path']);
    }
    // Always trailing slash the Front Page URL
    if (trailingslashit($redirect['path']) == trailingslashit($user_home['path'])) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Ignore differences in host capitalization, as this can lead to infinite redirects
    // Only redirect no-www <=> yes-www
    if (strtolower($original['host']) == strtolower($redirect['host']) || strtolower($original['host']) != 'www.' . strtolower($redirect['host']) && 'www.' . strtolower($original['host']) != strtolower($redirect['host'])) {
        $redirect['host'] = $original['host'];
    }
    $compare_original = array($original['host'], $original['path']);
    if (!empty($original['port'])) {
        $compare_original[] = $original['port'];
    }
    if (!empty($original['query'])) {
        $compare_original[] = $original['query'];
    }
    $compare_redirect = array($redirect['host'], $redirect['path']);
    if (!empty($redirect['port'])) {
        $compare_redirect[] = $redirect['port'];
    }
    if (!empty($redirect['query'])) {
        $compare_redirect[] = $redirect['query'];
    }
    if ($compare_original !== $compare_redirect) {
        $redirect_url = $redirect['scheme'] . '://' . $redirect['host'];
        if (!empty($redirect['port'])) {
            $redirect_url .= ':' . $redirect['port'];
        }
        $redirect_url .= $redirect['path'];
        if (!empty($redirect['query'])) {
            $redirect_url .= '?' . $redirect['query'];
        }
    }
    if (!$redirect_url || $redirect_url == $requested_url) {
        return;
    }
    // Hex encoded octets are case-insensitive.
    if (false !== strpos($requested_url, '%')) {
        if (!function_exists('lowercase_octets')) {
            function lowercase_octets($matches)
            {
                return strtolower($matches[0]);
            }
        }
        $requested_url = preg_replace_callback('|%[a-fA-F0-9][a-fA-F0-9]|', 'lowercase_octets', $requested_url);
    }
    /**
     * Filter the canonical redirect URL.
     *
     * Returning false to this filter will cancel the redirect.
     *
     * @since 2.3.0
     *
     * @param string $redirect_url  The redirect URL.
     * @param string $requested_url The requested URL.
     */
    $redirect_url = apply_filters('redirect_canonical', $redirect_url, $requested_url);
    // yes, again -- in case the filter aborted the request
    if (!$redirect_url || strip_fragment_from_url($redirect_url) == strip_fragment_from_url($requested_url)) {
        return;
    }
    if ($do_redirect) {
        // protect against chained redirects
        if (!redirect_canonical($redirect_url, false)) {
            wp_redirect($redirect_url, 301);
            exit;
        } else {
            // Debug
            // die("1: $redirect_url<br />2: " . redirect_canonical( $redirect_url, false ) );
            return;
        }
    } else {
        return $redirect_url;
    }
}

WordPress Version: 4.4

/**
 * Canonical API to handle WordPress Redirecting
 *
 * Based on "Permalink Redirect" from Scott Yang and "Enforce www. Preference"
 * by Mark Jaquith
 *
 * @package WordPress
 * @since 2.3.0
 */
/**
 * Redirects incoming links to the proper URL based on the site url.
 *
 * Search engines consider www.somedomain.com and somedomain.com to be two
 * different URLs when they both go to the same location. This SEO enhancement
 * prevents penalty for duplicate content by redirecting all incoming links to
 * one or the other.
 *
 * Prevents redirection for feeds, trackbacks, searches, comment popup, and
 * admin URLs. Does not redirect on non-pretty-permalink-supporting IIS 7+,
 * page/post previews, WP admin, Trackbacks, robots.txt, searches, or on POST
 * requests.
 *
 * Will also attempt to find the correct link when a user enters a URL that does
 * not exist based on exact WordPress query. Will instead try to parse the URL
 * or query in an attempt to figure the correct page to go to.
 *
 * @since 2.3.0
 *
 * @global WP_Rewrite $wp_rewrite
 * @global bool $is_IIS
 * @global WP_Query $wp_query
 * @global wpdb $wpdb WordPress database abstraction object.
 *
 * @param string $requested_url Optional. The URL that was requested, used to
 *		figure if redirect is needed.
 * @param bool $do_redirect Optional. Redirect to the new URL.
 * @return string|void The string of the URL, if redirect needed.
 */
function redirect_canonical($requested_url = null, $do_redirect = true)
{
    global $wp_rewrite, $is_IIS, $wp_query, $wpdb, $wp;
    if (isset($_SERVER['REQUEST_METHOD']) && !in_array(strtoupper($_SERVER['REQUEST_METHOD']), array('GET', 'HEAD'))) {
        return;
    }
    // If we're not in wp-admin and the post has been published and preview nonce
    // is non-existent or invalid then no need for preview in query
    if (is_preview() && get_query_var('p') && 'publish' == get_post_status(get_query_var('p'))) {
        if (!isset($_GET['preview_id']) || !isset($_GET['preview_nonce']) || !wp_verify_nonce($_GET['preview_nonce'], 'post_preview_' . (int) $_GET['preview_id'])) {
            $wp_query->is_preview = false;
        }
    }
    if (is_trackback() || is_search() || is_comments_popup() || is_admin() || is_preview() || is_robots() || $is_IIS && !iis7_supports_permalinks()) {
        return;
    }
    if (!$requested_url && isset($_SERVER['HTTP_HOST'])) {
        // build the URL in the address bar
        $requested_url = is_ssl() ? 'https://' : 'http://';
        $requested_url .= $_SERVER['HTTP_HOST'];
        $requested_url .= $_SERVER['REQUEST_URI'];
    }
    $original = @parse_url($requested_url);
    if (false === $original) {
        return;
    }
    $redirect = $original;
    $redirect_url = false;
    // Notice fixing
    if (!isset($redirect['path'])) {
        $redirect['path'] = '';
    }
    if (!isset($redirect['query'])) {
        $redirect['query'] = '';
    }
    // If the original URL ended with non-breaking spaces, they were almost
    // certainly inserted by accident. Let's remove them, so the reader doesn't
    // see a 404 error with no obvious cause.
    $redirect['path'] = preg_replace('|(%C2%A0)+$|i', '', $redirect['path']);
    // It's not a preview, so remove it from URL
    if (get_query_var('preview')) {
        $redirect['query'] = remove_query_arg('preview', $redirect['query']);
    }
    if (is_feed() && $id = get_query_var('p')) {
        if ($redirect_url = get_post_comments_feed_link($id, get_query_var('feed'))) {
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type', 'feed'), $redirect_url);
            $redirect['path'] = parse_url($redirect_url, PHP_URL_PATH);
        }
    }
    if (is_singular() && 1 > $wp_query->post_count && $id = get_query_var('p')) {
        $vars = $wpdb->get_results($wpdb->prepare("SELECT post_type, post_parent FROM {$wpdb->posts} WHERE ID = %d", $id));
        if (isset($vars[0]) && $vars = $vars[0]) {
            if ('revision' == $vars->post_type && $vars->post_parent > 0) {
                $id = $vars->post_parent;
            }
            if ($redirect_url = get_permalink($id)) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    }
    // These tests give us a WP-generated permalink
    if (is_404()) {
        // Redirect ?page_id, ?p=, ?attachment_id= to their respective url's
        $id = max(get_query_var('p'), get_query_var('page_id'), get_query_var('attachment_id'));
        if ($id && $redirect_post = get_post($id)) {
            $post_type_obj = get_post_type_object($redirect_post->post_type);
            if ($post_type_obj->public && 'auto-draft' != $redirect_post->post_status) {
                $redirect_url = get_permalink($redirect_post);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
        if (get_query_var('day') && get_query_var('monthnum') && get_query_var('year')) {
            $year = get_query_var('year');
            $month = get_query_var('monthnum');
            $day = get_query_var('day');
            $date = sprintf('%04d-%02d-%02d', $year, $month, $day);
            if (!wp_checkdate($month, $day, $year, $date)) {
                $redirect_url = get_month_link($year, $month);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum', 'day'), $redirect_url);
            }
        } elseif (get_query_var('monthnum') && get_query_var('year') && 12 < get_query_var('monthnum')) {
            $redirect_url = get_year_link(get_query_var('year'));
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum'), $redirect_url);
        }
        if (!$redirect_url) {
            if ($redirect_url = redirect_guess_404_permalink()) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('page', 'feed', 'p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
        if (get_query_var('page') && $wp_query->post && false !== strpos($wp_query->post->post_content, '<!--nextpage-->')) {
            $redirect['path'] = rtrim($redirect['path'], (int) get_query_var('page') . '/');
            $redirect['query'] = remove_query_arg('page', $redirect['query']);
            $redirect_url = get_permalink($wp_query->post->ID);
        }
    } elseif (is_object($wp_rewrite) && $wp_rewrite->using_permalinks()) {
        // rewriting of old ?p=X, ?m=2004, ?m=200401, ?m=20040101
        if (is_attachment() && !array_diff(array_keys($wp->query_vars), array('attachment', 'attachment_id')) && !$redirect_url) {
            if (!empty($_GET['attachment_id'])) {
                $redirect_url = get_attachment_link(get_query_var('attachment_id'));
                if ($redirect_url) {
                    $redirect['query'] = remove_query_arg('attachment_id', $redirect['query']);
                }
            } else {
                $redirect_url = get_attachment_link();
            }
        } elseif (is_single() && !empty($_GET['p']) && !$redirect_url) {
            if ($redirect_url = get_permalink(get_query_var('p'))) {
                $redirect['query'] = remove_query_arg(array('p', 'post_type'), $redirect['query']);
            }
        } elseif (is_single() && !empty($_GET['name']) && !$redirect_url) {
            if ($redirect_url = get_permalink($wp_query->get_queried_object_id())) {
                $redirect['query'] = remove_query_arg('name', $redirect['query']);
            }
        } elseif (is_page() && !empty($_GET['page_id']) && !$redirect_url) {
            if ($redirect_url = get_permalink(get_query_var('page_id'))) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (is_page() && !is_feed() && isset($wp_query->queried_object) && 'page' == get_option('show_on_front') && $wp_query->queried_object->ID == get_option('page_on_front') && !$redirect_url) {
            $redirect_url = home_url('/');
        } elseif (is_home() && !empty($_GET['page_id']) && 'page' == get_option('show_on_front') && get_query_var('page_id') == get_option('page_for_posts') && !$redirect_url) {
            if ($redirect_url = get_permalink(get_option('page_for_posts'))) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (!empty($_GET['m']) && (is_year() || is_month() || is_day())) {
            $m = get_query_var('m');
            switch (strlen($m)) {
                case 4:
                    // Yearly
                    $redirect_url = get_year_link($m);
                    break;
                case 6:
                    // Monthly
                    $redirect_url = get_month_link(substr($m, 0, 4), substr($m, 4, 2));
                    break;
                case 8:
                    // Daily
                    $redirect_url = get_day_link(substr($m, 0, 4), substr($m, 4, 2), substr($m, 6, 2));
                    break;
            }
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('m', $redirect['query']);
            }
            // now moving on to non ?m=X year/month/day links
        } elseif (is_day() && get_query_var('year') && get_query_var('monthnum') && !empty($_GET['day'])) {
            if ($redirect_url = get_day_link(get_query_var('year'), get_query_var('monthnum'), get_query_var('day'))) {
                $redirect['query'] = remove_query_arg(array('year', 'monthnum', 'day'), $redirect['query']);
            }
        } elseif (is_month() && get_query_var('year') && !empty($_GET['monthnum'])) {
            if ($redirect_url = get_month_link(get_query_var('year'), get_query_var('monthnum'))) {
                $redirect['query'] = remove_query_arg(array('year', 'monthnum'), $redirect['query']);
            }
        } elseif (is_year() && !empty($_GET['year'])) {
            if ($redirect_url = get_year_link(get_query_var('year'))) {
                $redirect['query'] = remove_query_arg('year', $redirect['query']);
            }
        } elseif (is_author() && !empty($_GET['author']) && preg_match('|^[0-9]+$|', $_GET['author'])) {
            $author = get_userdata(get_query_var('author'));
            if (false !== $author && $wpdb->get_var($wpdb->prepare("SELECT ID FROM {$wpdb->posts} WHERE {$wpdb->posts}.post_author = %d AND {$wpdb->posts}.post_status = 'publish' LIMIT 1", $author->ID))) {
                if ($redirect_url = get_author_posts_url($author->ID, $author->user_nicename)) {
                    $redirect['query'] = remove_query_arg('author', $redirect['query']);
                }
            }
        } elseif (is_category() || is_tag() || is_tax()) {
            // Terms (Tags/categories)
            $term_count = 0;
            foreach ($wp_query->tax_query->queried_terms as $tax_query) {
                $term_count += count($tax_query['terms']);
            }
            $obj = $wp_query->get_queried_object();
            if ($term_count <= 1 && !empty($obj->term_id) && ($tax_url = get_term_link((int) $obj->term_id, $obj->taxonomy)) && !is_wp_error($tax_url)) {
                if (!empty($redirect['query'])) {
                    // Strip taxonomy query vars off the url.
                    $qv_remove = array('term', 'taxonomy');
                    if (is_category()) {
                        $qv_remove[] = 'category_name';
                        $qv_remove[] = 'cat';
                    } elseif (is_tag()) {
                        $qv_remove[] = 'tag';
                        $qv_remove[] = 'tag_id';
                    } else {
                        // Custom taxonomies will have a custom query var, remove those too:
                        $tax_obj = get_taxonomy($obj->taxonomy);
                        if (false !== $tax_obj->query_var) {
                            $qv_remove[] = $tax_obj->query_var;
                        }
                    }
                    $rewrite_vars = array_diff(array_keys($wp_query->query), array_keys($_GET));
                    if (!array_diff($rewrite_vars, array_keys($_GET))) {
                        // Check to see if all the Query vars are coming from the rewrite, none are set via $_GET
                        $redirect['query'] = remove_query_arg($qv_remove, $redirect['query']);
                        //Remove all of the per-tax qv's
                        // Create the destination url for this taxonomy
                        $tax_url = parse_url($tax_url);
                        if (!empty($tax_url['query'])) {
                            // Taxonomy accessible via ?taxonomy=..&term=.. or any custom qv..
                            parse_str($tax_url['query'], $query_vars);
                            $redirect['query'] = add_query_arg($query_vars, $redirect['query']);
                        } else {
                            // Taxonomy is accessible via a "pretty-URL"
                            $redirect['path'] = $tax_url['path'];
                        }
                    } else {
                        // Some query vars are set via $_GET. Unset those from $_GET that exist via the rewrite
                        foreach ($qv_remove as $_qv) {
                            if (isset($rewrite_vars[$_qv])) {
                                $redirect['query'] = remove_query_arg($_qv, $redirect['query']);
                            }
                        }
                    }
                }
            }
        } elseif (is_single() && strpos($wp_rewrite->permalink_structure, '%category%') !== false && $cat = get_query_var('category_name')) {
            $category = get_category_by_path($cat);
            $post_terms = wp_get_object_terms($wp_query->get_queried_object_id(), 'category', array('fields' => 'tt_ids'));
            if (!$category || is_wp_error($category) || !is_wp_error($post_terms) && !empty($post_terms) && !in_array($category->term_taxonomy_id, $post_terms)) {
                $redirect_url = get_permalink($wp_query->get_queried_object_id());
            }
        }
        // Post Paging
        if (is_singular() && !is_front_page() && get_query_var('page')) {
            if (!$redirect_url) {
                $redirect_url = get_permalink(get_queried_object_id());
            }
            $redirect_url = trailingslashit($redirect_url) . user_trailingslashit(get_query_var('page'), 'single_paged');
            $redirect['query'] = remove_query_arg('page', $redirect['query']);
        }
        // paging and feeds
        if (get_query_var('paged') || is_feed() || get_query_var('cpage')) {
            while (preg_match("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", $redirect['path']) || preg_match('#/(comments/?)?(feed|rss|rdf|atom|rss2)(/+)?$#', $redirect['path']) || preg_match("#/{$wp_rewrite->comments_pagination_base}-[0-9]+(/+)?\$#", $redirect['path'])) {
                // Strip off paging and feed
                $redirect['path'] = preg_replace("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", '/', $redirect['path']);
                // strip off any existing paging
                $redirect['path'] = preg_replace('#/(comments/?)?(feed|rss2?|rdf|atom)(/+|$)#', '/', $redirect['path']);
                // strip off feed endings
                $redirect['path'] = preg_replace("#/{$wp_rewrite->comments_pagination_base}-[0-9]+?(/+)?\$#", '/', $redirect['path']);
                // strip off any existing comment paging
            }
            $addl_path = '';
            if (is_feed() && in_array(get_query_var('feed'), $wp_rewrite->feeds)) {
                $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                if (!is_singular() && get_query_var('withcomments')) {
                    $addl_path .= 'comments/';
                }
                if ('rss' == get_default_feed() && 'feed' == get_query_var('feed') || 'rss' == get_query_var('feed')) {
                    $addl_path .= user_trailingslashit('feed/' . ((get_default_feed() == 'rss2') ? '' : 'rss2'), 'feed');
                } else {
                    $addl_path .= user_trailingslashit('feed/' . ((get_default_feed() == get_query_var('feed') || 'feed' == get_query_var('feed')) ? '' : get_query_var('feed')), 'feed');
                }
                $redirect['query'] = remove_query_arg('feed', $redirect['query']);
            } elseif (is_feed() && 'old' == get_query_var('feed')) {
                $old_feed_files = array('wp-atom.php' => 'atom', 'wp-commentsrss2.php' => 'comments_rss2', 'wp-feed.php' => get_default_feed(), 'wp-rdf.php' => 'rdf', 'wp-rss.php' => 'rss2', 'wp-rss2.php' => 'rss2');
                if (isset($old_feed_files[basename($redirect['path'])])) {
                    $redirect_url = get_feed_link($old_feed_files[basename($redirect['path'])]);
                    wp_redirect($redirect_url, 301);
                    die;
                }
            }
            if (get_query_var('paged') > 0) {
                $paged = get_query_var('paged');
                $redirect['query'] = remove_query_arg('paged', $redirect['query']);
                if (!is_feed()) {
                    if ($paged > 1 && !is_single()) {
                        $addl_path = ((!empty($addl_path)) ? trailingslashit($addl_path) : '') . user_trailingslashit("{$wp_rewrite->pagination_base}/{$paged}", 'paged');
                    } elseif (!is_single()) {
                        $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                    }
                } elseif ($paged > 1) {
                    $redirect['query'] = add_query_arg('paged', $paged, $redirect['query']);
                }
            }
            if (get_option('page_comments') && ('newest' == get_option('default_comments_page') && get_query_var('cpage') > 0 || 'newest' != get_option('default_comments_page') && get_query_var('cpage') > 1)) {
                $addl_path = ((!empty($addl_path)) ? trailingslashit($addl_path) : '') . user_trailingslashit($wp_rewrite->comments_pagination_base . '-' . get_query_var('cpage'), 'commentpaged');
                $redirect['query'] = remove_query_arg('cpage', $redirect['query']);
            }
            $redirect['path'] = user_trailingslashit(preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/?$|', '/', $redirect['path']));
            // strip off trailing /index.php/
            if (!empty($addl_path) && $wp_rewrite->using_index_permalinks() && strpos($redirect['path'], '/' . $wp_rewrite->index . '/') === false) {
                $redirect['path'] = trailingslashit($redirect['path']) . $wp_rewrite->index . '/';
            }
            if (!empty($addl_path)) {
                $redirect['path'] = trailingslashit($redirect['path']) . $addl_path;
            }
            $redirect_url = $redirect['scheme'] . '://' . $redirect['host'] . $redirect['path'];
        }
        if ('wp-register.php' == basename($redirect['path'])) {
            if (is_multisite()) {
                /** This filter is documented in wp-login.php */
                $redirect_url = apply_filters('wp_signup_location', network_site_url('wp-signup.php'));
            } else {
                $redirect_url = wp_registration_url();
            }
            wp_redirect($redirect_url, 301);
            die;
        }
    }
    // tack on any additional query vars
    $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    if ($redirect_url && !empty($redirect['query'])) {
        parse_str($redirect['query'], $_parsed_query);
        $redirect = @parse_url($redirect_url);
        if (!empty($_parsed_query['name']) && !empty($redirect['query'])) {
            parse_str($redirect['query'], $_parsed_redirect_query);
            if (empty($_parsed_redirect_query['name'])) {
                unset($_parsed_query['name']);
            }
        }
        $_parsed_query = rawurlencode_deep($_parsed_query);
        $redirect_url = add_query_arg($_parsed_query, $redirect_url);
    }
    if ($redirect_url) {
        $redirect = @parse_url($redirect_url);
    }
    // www.example.com vs example.com
    $user_home = @parse_url(home_url());
    if (!empty($user_home['host'])) {
        $redirect['host'] = $user_home['host'];
    }
    if (empty($user_home['path'])) {
        $user_home['path'] = '/';
    }
    // Handle ports
    if (!empty($user_home['port'])) {
        $redirect['port'] = $user_home['port'];
    } else {
        unset($redirect['port']);
    }
    // trailing /index.php
    $redirect['path'] = preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/*?$|', '/', $redirect['path']);
    // Remove trailing spaces from the path
    $redirect['path'] = preg_replace('#(%20| )+$#', '', $redirect['path']);
    if (!empty($redirect['query'])) {
        // Remove trailing spaces from certain terminating query string args
        $redirect['query'] = preg_replace('#((p|page_id|cat|tag)=[^&]*?)(%20| )+$#', '$1', $redirect['query']);
        // Clean up empty query strings
        $redirect['query'] = trim(preg_replace('#(^|&)(p|page_id|cat|tag)=?(&|$)#', '&', $redirect['query']), '&');
        // Redirect obsolete feeds
        $redirect['query'] = preg_replace('#(^|&)feed=rss(&|$)#', '$1feed=rss2$2', $redirect['query']);
        // Remove redundant leading ampersands
        $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    }
    // strip /index.php/ when we're not using PATHINFO permalinks
    if (!$wp_rewrite->using_index_permalinks()) {
        $redirect['path'] = str_replace('/' . $wp_rewrite->index . '/', '/', $redirect['path']);
    }
    // trailing slashes
    if (is_object($wp_rewrite) && $wp_rewrite->using_permalinks() && !is_404() && (!is_front_page() || is_front_page() && get_query_var('paged') > 1)) {
        $user_ts_type = '';
        if (get_query_var('paged') > 0) {
            $user_ts_type = 'paged';
        } else {
            foreach (array('single', 'category', 'page', 'day', 'month', 'year', 'home') as $type) {
                $func = 'is_' . $type;
                if (call_user_func($func)) {
                    $user_ts_type = $type;
                    break;
                }
            }
        }
        $redirect['path'] = user_trailingslashit($redirect['path'], $user_ts_type);
    } elseif (is_front_page()) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Strip multiple slashes out of the URL
    if (strpos($redirect['path'], '//') > -1) {
        $redirect['path'] = preg_replace('|/+|', '/', $redirect['path']);
    }
    // Always trailing slash the Front Page URL
    if (trailingslashit($redirect['path']) == trailingslashit($user_home['path'])) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Ignore differences in host capitalization, as this can lead to infinite redirects
    // Only redirect no-www <=> yes-www
    if (strtolower($original['host']) == strtolower($redirect['host']) || strtolower($original['host']) != 'www.' . strtolower($redirect['host']) && 'www.' . strtolower($original['host']) != strtolower($redirect['host'])) {
        $redirect['host'] = $original['host'];
    }
    $compare_original = array($original['host'], $original['path']);
    if (!empty($original['port'])) {
        $compare_original[] = $original['port'];
    }
    if (!empty($original['query'])) {
        $compare_original[] = $original['query'];
    }
    $compare_redirect = array($redirect['host'], $redirect['path']);
    if (!empty($redirect['port'])) {
        $compare_redirect[] = $redirect['port'];
    }
    if (!empty($redirect['query'])) {
        $compare_redirect[] = $redirect['query'];
    }
    if ($compare_original !== $compare_redirect) {
        $redirect_url = $redirect['scheme'] . '://' . $redirect['host'];
        if (!empty($redirect['port'])) {
            $redirect_url .= ':' . $redirect['port'];
        }
        $redirect_url .= $redirect['path'];
        if (!empty($redirect['query'])) {
            $redirect_url .= '?' . $redirect['query'];
        }
    }
    if (!$redirect_url || $redirect_url == $requested_url) {
        return;
    }
    // Hex encoded octets are case-insensitive.
    if (false !== strpos($requested_url, '%')) {
        if (!function_exists('lowercase_octets')) {
            function lowercase_octets($matches)
            {
                return strtolower($matches[0]);
            }
        }
        $requested_url = preg_replace_callback('|%[a-fA-F0-9][a-fA-F0-9]|', 'lowercase_octets', $requested_url);
    }
    /**
     * Filter the canonical redirect URL.
     *
     * Returning false to this filter will cancel the redirect.
     *
     * @since 2.3.0
     *
     * @param string $redirect_url  The redirect URL.
     * @param string $requested_url The requested URL.
     */
    $redirect_url = apply_filters('redirect_canonical', $redirect_url, $requested_url);
    // yes, again -- in case the filter aborted the request
    if (!$redirect_url || strip_fragment_from_url($redirect_url) == strip_fragment_from_url($requested_url)) {
        return;
    }
    if ($do_redirect) {
        // protect against chained redirects
        if (!redirect_canonical($redirect_url, false)) {
            wp_redirect($redirect_url, 301);
            exit;
        } else {
            // Debug
            // die("1: $redirect_url<br />2: " . redirect_canonical( $redirect_url, false ) );
            return;
        }
    } else {
        return $redirect_url;
    }
}

WordPress Version: 4.3

/**
 * Canonical API to handle WordPress Redirecting
 *
 * Based on "Permalink Redirect" from Scott Yang and "Enforce www. Preference"
 * by Mark Jaquith
 *
 * @package WordPress
 * @since 2.3.0
 */
/**
 * Redirects incoming links to the proper URL based on the site url.
 *
 * Search engines consider www.somedomain.com and somedomain.com to be two
 * different URLs when they both go to the same location. This SEO enhancement
 * prevents penalty for duplicate content by redirecting all incoming links to
 * one or the other.
 *
 * Prevents redirection for feeds, trackbacks, searches, comment popup, and
 * admin URLs. Does not redirect on non-pretty-permalink-supporting IIS 7+,
 * page/post previews, WP admin, Trackbacks, robots.txt, searches, or on POST
 * requests.
 *
 * Will also attempt to find the correct link when a user enters a URL that does
 * not exist based on exact WordPress query. Will instead try to parse the URL
 * or query in an attempt to figure the correct page to go to.
 *
 * @since 2.3.0
 *
 * @global WP_Rewrite $wp_rewrite
 * @global bool $is_IIS
 * @global WP_Query $wp_query
 * @global wpdb $wpdb
 *
 * @param string $requested_url Optional. The URL that was requested, used to
 *		figure if redirect is needed.
 * @param bool $do_redirect Optional. Redirect to the new URL.
 * @return string|void The string of the URL, if redirect needed.
 */
function redirect_canonical($requested_url = null, $do_redirect = true)
{
    global $wp_rewrite, $is_IIS, $wp_query, $wpdb;
    if (isset($_SERVER['REQUEST_METHOD']) && !in_array(strtoupper($_SERVER['REQUEST_METHOD']), array('GET', 'HEAD'))) {
        return;
    }
    // If we're not in wp-admin and the post has been published and preview nonce
    // is non-existent or invalid then no need for preview in query
    if (is_preview() && get_query_var('p') && 'publish' == get_post_status(get_query_var('p'))) {
        if (!isset($_GET['preview_id']) || !isset($_GET['preview_nonce']) || !wp_verify_nonce($_GET['preview_nonce'], 'post_preview_' . (int) $_GET['preview_id'])) {
            $wp_query->is_preview = false;
        }
    }
    if (is_trackback() || is_search() || is_comments_popup() || is_admin() || is_preview() || is_robots() || $is_IIS && !iis7_supports_permalinks()) {
        return;
    }
    if (!$requested_url) {
        // build the URL in the address bar
        $requested_url = is_ssl() ? 'https://' : 'http://';
        $requested_url .= $_SERVER['HTTP_HOST'];
        $requested_url .= $_SERVER['REQUEST_URI'];
    }
    $original = @parse_url($requested_url);
    if (false === $original) {
        return;
    }
    // Some PHP setups turn requests for / into /index.php in REQUEST_URI
    // See: https://core.trac.wordpress.org/ticket/5017
    // See: https://core.trac.wordpress.org/ticket/7173
    // Disabled, for now:
    // $original['path'] = preg_replace('|/index\.php$|', '/', $original['path']);
    $redirect = $original;
    $redirect_url = false;
    // Notice fixing
    if (!isset($redirect['path'])) {
        $redirect['path'] = '';
    }
    if (!isset($redirect['query'])) {
        $redirect['query'] = '';
    }
    // If the original URL ended with non-breaking spaces, they were almost
    // certainly inserted by accident. Let's remove them, so the reader doesn't
    // see a 404 error with no obvious cause.
    $redirect['path'] = preg_replace('|(%C2%A0)+$|i', '', $redirect['path']);
    // It's not a preview, so remove it from URL
    if (get_query_var('preview')) {
        $redirect['query'] = remove_query_arg('preview', $redirect['query']);
    }
    if (is_feed() && $id = get_query_var('p')) {
        if ($redirect_url = get_post_comments_feed_link($id, get_query_var('feed'))) {
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type', 'feed'), $redirect_url);
            $redirect['path'] = parse_url($redirect_url, PHP_URL_PATH);
        }
    }
    if (is_singular() && 1 > $wp_query->post_count && $id = get_query_var('p')) {
        $vars = $wpdb->get_results($wpdb->prepare("SELECT post_type, post_parent FROM {$wpdb->posts} WHERE ID = %d", $id));
        if (isset($vars[0]) && $vars = $vars[0]) {
            if ('revision' == $vars->post_type && $vars->post_parent > 0) {
                $id = $vars->post_parent;
            }
            if ($redirect_url = get_permalink($id)) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    }
    // These tests give us a WP-generated permalink
    if (is_404()) {
        // Redirect ?page_id, ?p=, ?attachment_id= to their respective url's
        $id = max(get_query_var('p'), get_query_var('page_id'), get_query_var('attachment_id'));
        if ($id && $redirect_post = get_post($id)) {
            $post_type_obj = get_post_type_object($redirect_post->post_type);
            if ($post_type_obj->public) {
                $redirect_url = get_permalink($redirect_post);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
        if (get_query_var('day') && get_query_var('monthnum') && get_query_var('year')) {
            $year = get_query_var('year');
            $month = get_query_var('monthnum');
            $day = get_query_var('day');
            $date = sprintf('%04d-%02d-%02d', $year, $month, $day);
            if (!wp_checkdate($month, $day, $year, $date)) {
                $redirect_url = get_month_link($year, $month);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum', 'day'), $redirect_url);
            }
        } elseif (get_query_var('monthnum') && get_query_var('year') && 12 < get_query_var('monthnum')) {
            $redirect_url = get_year_link(get_query_var('year'));
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum'), $redirect_url);
        }
        if (!$redirect_url) {
            if ($redirect_url = redirect_guess_404_permalink()) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('page', 'feed', 'p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    } elseif (is_object($wp_rewrite) && $wp_rewrite->using_permalinks()) {
        // rewriting of old ?p=X, ?m=2004, ?m=200401, ?m=20040101
        if (is_attachment() && !empty($_GET['attachment_id']) && !$redirect_url) {
            if ($redirect_url = get_attachment_link(get_query_var('attachment_id'))) {
                $redirect['query'] = remove_query_arg('attachment_id', $redirect['query']);
            }
        } elseif (is_single() && !empty($_GET['p']) && !$redirect_url) {
            if ($redirect_url = get_permalink(get_query_var('p'))) {
                $redirect['query'] = remove_query_arg(array('p', 'post_type'), $redirect['query']);
            }
        } elseif (is_single() && !empty($_GET['name']) && !$redirect_url) {
            if ($redirect_url = get_permalink($wp_query->get_queried_object_id())) {
                $redirect['query'] = remove_query_arg('name', $redirect['query']);
            }
        } elseif (is_page() && !empty($_GET['page_id']) && !$redirect_url) {
            if ($redirect_url = get_permalink(get_query_var('page_id'))) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (is_page() && !is_feed() && isset($wp_query->queried_object) && 'page' == get_option('show_on_front') && $wp_query->queried_object->ID == get_option('page_on_front') && !$redirect_url) {
            $redirect_url = home_url('/');
        } elseif (is_home() && !empty($_GET['page_id']) && 'page' == get_option('show_on_front') && get_query_var('page_id') == get_option('page_for_posts') && !$redirect_url) {
            if ($redirect_url = get_permalink(get_option('page_for_posts'))) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (!empty($_GET['m']) && (is_year() || is_month() || is_day())) {
            $m = get_query_var('m');
            switch (strlen($m)) {
                case 4:
                    // Yearly
                    $redirect_url = get_year_link($m);
                    break;
                case 6:
                    // Monthly
                    $redirect_url = get_month_link(substr($m, 0, 4), substr($m, 4, 2));
                    break;
                case 8:
                    // Daily
                    $redirect_url = get_day_link(substr($m, 0, 4), substr($m, 4, 2), substr($m, 6, 2));
                    break;
            }
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('m', $redirect['query']);
            }
            // now moving on to non ?m=X year/month/day links
        } elseif (is_day() && get_query_var('year') && get_query_var('monthnum') && !empty($_GET['day'])) {
            if ($redirect_url = get_day_link(get_query_var('year'), get_query_var('monthnum'), get_query_var('day'))) {
                $redirect['query'] = remove_query_arg(array('year', 'monthnum', 'day'), $redirect['query']);
            }
        } elseif (is_month() && get_query_var('year') && !empty($_GET['monthnum'])) {
            if ($redirect_url = get_month_link(get_query_var('year'), get_query_var('monthnum'))) {
                $redirect['query'] = remove_query_arg(array('year', 'monthnum'), $redirect['query']);
            }
        } elseif (is_year() && !empty($_GET['year'])) {
            if ($redirect_url = get_year_link(get_query_var('year'))) {
                $redirect['query'] = remove_query_arg('year', $redirect['query']);
            }
        } elseif (is_author() && !empty($_GET['author']) && preg_match('|^[0-9]+$|', $_GET['author'])) {
            $author = get_userdata(get_query_var('author'));
            if (false !== $author && $wpdb->get_var($wpdb->prepare("SELECT ID FROM {$wpdb->posts} WHERE {$wpdb->posts}.post_author = %d AND {$wpdb->posts}.post_status = 'publish' LIMIT 1", $author->ID))) {
                if ($redirect_url = get_author_posts_url($author->ID, $author->user_nicename)) {
                    $redirect['query'] = remove_query_arg('author', $redirect['query']);
                }
            }
        } elseif (is_category() || is_tag() || is_tax()) {
            // Terms (Tags/categories)
            $term_count = 0;
            foreach ($wp_query->tax_query->queried_terms as $tax_query) {
                $term_count += count($tax_query['terms']);
            }
            $obj = $wp_query->get_queried_object();
            if ($term_count <= 1 && !empty($obj->term_id) && ($tax_url = get_term_link((int) $obj->term_id, $obj->taxonomy)) && !is_wp_error($tax_url)) {
                if (!empty($redirect['query'])) {
                    // Strip taxonomy query vars off the url.
                    $qv_remove = array('term', 'taxonomy');
                    if (is_category()) {
                        $qv_remove[] = 'category_name';
                        $qv_remove[] = 'cat';
                    } elseif (is_tag()) {
                        $qv_remove[] = 'tag';
                        $qv_remove[] = 'tag_id';
                    } else {
                        // Custom taxonomies will have a custom query var, remove those too:
                        $tax_obj = get_taxonomy($obj->taxonomy);
                        if (false !== $tax_obj->query_var) {
                            $qv_remove[] = $tax_obj->query_var;
                        }
                    }
                    $rewrite_vars = array_diff(array_keys($wp_query->query), array_keys($_GET));
                    if (!array_diff($rewrite_vars, array_keys($_GET))) {
                        // Check to see if all the Query vars are coming from the rewrite, none are set via $_GET
                        $redirect['query'] = remove_query_arg($qv_remove, $redirect['query']);
                        //Remove all of the per-tax qv's
                        // Create the destination url for this taxonomy
                        $tax_url = parse_url($tax_url);
                        if (!empty($tax_url['query'])) {
                            // Taxonomy accessible via ?taxonomy=..&term=.. or any custom qv..
                            parse_str($tax_url['query'], $query_vars);
                            $redirect['query'] = add_query_arg($query_vars, $redirect['query']);
                        } else {
                            // Taxonomy is accessible via a "pretty-URL"
                            $redirect['path'] = $tax_url['path'];
                        }
                    } else {
                        // Some query vars are set via $_GET. Unset those from $_GET that exist via the rewrite
                        foreach ($qv_remove as $_qv) {
                            if (isset($rewrite_vars[$_qv])) {
                                $redirect['query'] = remove_query_arg($_qv, $redirect['query']);
                            }
                        }
                    }
                }
            }
        } elseif (is_single() && strpos($wp_rewrite->permalink_structure, '%category%') !== false && $cat = get_query_var('category_name')) {
            $category = get_category_by_path($cat);
            $post_terms = wp_get_object_terms($wp_query->get_queried_object_id(), 'category', array('fields' => 'tt_ids'));
            if (!$category || is_wp_error($category) || !is_wp_error($post_terms) && !empty($post_terms) && !in_array($category->term_taxonomy_id, $post_terms)) {
                $redirect_url = get_permalink($wp_query->get_queried_object_id());
            }
        }
        // Post Paging
        if (is_singular() && !is_front_page() && get_query_var('page')) {
            if (!$redirect_url) {
                $redirect_url = get_permalink(get_queried_object_id());
            }
            $redirect_url = trailingslashit($redirect_url) . user_trailingslashit(get_query_var('page'), 'single_paged');
            $redirect['query'] = remove_query_arg('page', $redirect['query']);
        }
        // paging and feeds
        if (get_query_var('paged') || is_feed() || get_query_var('cpage')) {
            while (preg_match("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", $redirect['path']) || preg_match('#/(comments/?)?(feed|rss|rdf|atom|rss2)(/+)?$#', $redirect['path']) || preg_match("#/{$wp_rewrite->comments_pagination_base}-[0-9]+(/+)?\$#", $redirect['path'])) {
                // Strip off paging and feed
                $redirect['path'] = preg_replace("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", '/', $redirect['path']);
                // strip off any existing paging
                $redirect['path'] = preg_replace('#/(comments/?)?(feed|rss2?|rdf|atom)(/+|$)#', '/', $redirect['path']);
                // strip off feed endings
                $redirect['path'] = preg_replace("#/{$wp_rewrite->comments_pagination_base}-[0-9]+?(/+)?\$#", '/', $redirect['path']);
                // strip off any existing comment paging
            }
            $addl_path = '';
            if (is_feed() && in_array(get_query_var('feed'), $wp_rewrite->feeds)) {
                $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                if (!is_singular() && get_query_var('withcomments')) {
                    $addl_path .= 'comments/';
                }
                if ('rss' == get_default_feed() && 'feed' == get_query_var('feed') || 'rss' == get_query_var('feed')) {
                    $addl_path .= user_trailingslashit('feed/' . ((get_default_feed() == 'rss2') ? '' : 'rss2'), 'feed');
                } else {
                    $addl_path .= user_trailingslashit('feed/' . ((get_default_feed() == get_query_var('feed') || 'feed' == get_query_var('feed')) ? '' : get_query_var('feed')), 'feed');
                }
                $redirect['query'] = remove_query_arg('feed', $redirect['query']);
            } elseif (is_feed() && 'old' == get_query_var('feed')) {
                $old_feed_files = array('wp-atom.php' => 'atom', 'wp-commentsrss2.php' => 'comments_rss2', 'wp-feed.php' => get_default_feed(), 'wp-rdf.php' => 'rdf', 'wp-rss.php' => 'rss2', 'wp-rss2.php' => 'rss2');
                if (isset($old_feed_files[basename($redirect['path'])])) {
                    $redirect_url = get_feed_link($old_feed_files[basename($redirect['path'])]);
                    wp_redirect($redirect_url, 301);
                    die;
                }
            }
            if (get_query_var('paged') > 0) {
                $paged = get_query_var('paged');
                $redirect['query'] = remove_query_arg('paged', $redirect['query']);
                if (!is_feed()) {
                    if ($paged > 1 && !is_single()) {
                        $addl_path = ((!empty($addl_path)) ? trailingslashit($addl_path) : '') . user_trailingslashit("{$wp_rewrite->pagination_base}/{$paged}", 'paged');
                    } elseif (!is_single()) {
                        $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                    }
                } elseif ($paged > 1) {
                    $redirect['query'] = add_query_arg('paged', $paged, $redirect['query']);
                }
            }
            if (get_option('page_comments') && ('newest' == get_option('default_comments_page') && get_query_var('cpage') > 0 || 'newest' != get_option('default_comments_page') && get_query_var('cpage') > 1)) {
                $addl_path = ((!empty($addl_path)) ? trailingslashit($addl_path) : '') . user_trailingslashit($wp_rewrite->comments_pagination_base . '-' . get_query_var('cpage'), 'commentpaged');
                $redirect['query'] = remove_query_arg('cpage', $redirect['query']);
            }
            $redirect['path'] = user_trailingslashit(preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/?$|', '/', $redirect['path']));
            // strip off trailing /index.php/
            if (!empty($addl_path) && $wp_rewrite->using_index_permalinks() && strpos($redirect['path'], '/' . $wp_rewrite->index . '/') === false) {
                $redirect['path'] = trailingslashit($redirect['path']) . $wp_rewrite->index . '/';
            }
            if (!empty($addl_path)) {
                $redirect['path'] = trailingslashit($redirect['path']) . $addl_path;
            }
            $redirect_url = $redirect['scheme'] . '://' . $redirect['host'] . $redirect['path'];
        }
        if ('wp-register.php' == basename($redirect['path'])) {
            if (is_multisite()) {
                /** This filter is documented in wp-login.php */
                $redirect_url = apply_filters('wp_signup_location', network_site_url('wp-signup.php'));
            } else {
                $redirect_url = site_url('wp-login.php?action=register');
            }
            wp_redirect($redirect_url, 301);
            die;
        }
    }
    // tack on any additional query vars
    $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    if ($redirect_url && !empty($redirect['query'])) {
        parse_str($redirect['query'], $_parsed_query);
        $redirect = @parse_url($redirect_url);
        if (!empty($_parsed_query['name']) && !empty($redirect['query'])) {
            parse_str($redirect['query'], $_parsed_redirect_query);
            if (empty($_parsed_redirect_query['name'])) {
                unset($_parsed_query['name']);
            }
        }
        $_parsed_query = rawurlencode_deep($_parsed_query);
        $redirect_url = add_query_arg($_parsed_query, $redirect_url);
    }
    if ($redirect_url) {
        $redirect = @parse_url($redirect_url);
    }
    // www.example.com vs example.com
    $user_home = @parse_url(home_url());
    if (!empty($user_home['host'])) {
        $redirect['host'] = $user_home['host'];
    }
    if (empty($user_home['path'])) {
        $user_home['path'] = '/';
    }
    // Handle ports
    if (!empty($user_home['port'])) {
        $redirect['port'] = $user_home['port'];
    } else {
        unset($redirect['port']);
    }
    // trailing /index.php
    $redirect['path'] = preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/*?$|', '/', $redirect['path']);
    // Remove trailing spaces from the path
    $redirect['path'] = preg_replace('#(%20| )+$#', '', $redirect['path']);
    if (!empty($redirect['query'])) {
        // Remove trailing spaces from certain terminating query string args
        $redirect['query'] = preg_replace('#((p|page_id|cat|tag)=[^&]*?)(%20| )+$#', '$1', $redirect['query']);
        // Clean up empty query strings
        $redirect['query'] = trim(preg_replace('#(^|&)(p|page_id|cat|tag)=?(&|$)#', '&', $redirect['query']), '&');
        // Redirect obsolete feeds
        $redirect['query'] = preg_replace('#(^|&)feed=rss(&|$)#', '$1feed=rss2$2', $redirect['query']);
        // Remove redundant leading ampersands
        $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    }
    // strip /index.php/ when we're not using PATHINFO permalinks
    if (!$wp_rewrite->using_index_permalinks()) {
        $redirect['path'] = str_replace('/' . $wp_rewrite->index . '/', '/', $redirect['path']);
    }
    // trailing slashes
    if (is_object($wp_rewrite) && $wp_rewrite->using_permalinks() && !is_404() && (!is_front_page() || is_front_page() && get_query_var('paged') > 1)) {
        $user_ts_type = '';
        if (get_query_var('paged') > 0) {
            $user_ts_type = 'paged';
        } else {
            foreach (array('single', 'category', 'page', 'day', 'month', 'year', 'home') as $type) {
                $func = 'is_' . $type;
                if (call_user_func($func)) {
                    $user_ts_type = $type;
                    break;
                }
            }
        }
        $redirect['path'] = user_trailingslashit($redirect['path'], $user_ts_type);
    } elseif (is_front_page()) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Strip multiple slashes out of the URL
    if (strpos($redirect['path'], '//') > -1) {
        $redirect['path'] = preg_replace('|/+|', '/', $redirect['path']);
    }
    // Always trailing slash the Front Page URL
    if (trailingslashit($redirect['path']) == trailingslashit($user_home['path'])) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Ignore differences in host capitalization, as this can lead to infinite redirects
    // Only redirect no-www <=> yes-www
    if (strtolower($original['host']) == strtolower($redirect['host']) || strtolower($original['host']) != 'www.' . strtolower($redirect['host']) && 'www.' . strtolower($original['host']) != strtolower($redirect['host'])) {
        $redirect['host'] = $original['host'];
    }
    $compare_original = array($original['host'], $original['path']);
    if (!empty($original['port'])) {
        $compare_original[] = $original['port'];
    }
    if (!empty($original['query'])) {
        $compare_original[] = $original['query'];
    }
    $compare_redirect = array($redirect['host'], $redirect['path']);
    if (!empty($redirect['port'])) {
        $compare_redirect[] = $redirect['port'];
    }
    if (!empty($redirect['query'])) {
        $compare_redirect[] = $redirect['query'];
    }
    if ($compare_original !== $compare_redirect) {
        $redirect_url = $redirect['scheme'] . '://' . $redirect['host'];
        if (!empty($redirect['port'])) {
            $redirect_url .= ':' . $redirect['port'];
        }
        $redirect_url .= $redirect['path'];
        if (!empty($redirect['query'])) {
            $redirect_url .= '?' . $redirect['query'];
        }
    }
    if (!$redirect_url || $redirect_url == $requested_url) {
        return;
    }
    // Hex encoded octets are case-insensitive.
    if (false !== strpos($requested_url, '%')) {
        if (!function_exists('lowercase_octets')) {
            function lowercase_octets($matches)
            {
                return strtolower($matches[0]);
            }
        }
        $requested_url = preg_replace_callback('|%[a-fA-F0-9][a-fA-F0-9]|', 'lowercase_octets', $requested_url);
    }
    /**
     * Filter the canonical redirect URL.
     *
     * Returning false to this filter will cancel the redirect.
     *
     * @since 2.3.0
     *
     * @param string $redirect_url  The redirect URL.
     * @param string $requested_url The requested URL.
     */
    $redirect_url = apply_filters('redirect_canonical', $redirect_url, $requested_url);
    // yes, again -- in case the filter aborted the request
    if (!$redirect_url || $redirect_url == $requested_url) {
        return;
    }
    if ($do_redirect) {
        // protect against chained redirects
        if (!redirect_canonical($redirect_url, false)) {
            wp_redirect($redirect_url, 301);
            exit;
        } else {
            // Debug
            // die("1: $redirect_url<br />2: " . redirect_canonical( $redirect_url, false ) );
            return;
        }
    } else {
        return $redirect_url;
    }
}

WordPress Version: 4.2

/**
 * Canonical API to handle WordPress Redirecting
 *
 * Based on "Permalink Redirect" from Scott Yang and "Enforce www. Preference"
 * by Mark Jaquith
 *
 * @package WordPress
 * @since 2.3.0
 */
/**
 * Redirects incoming links to the proper URL based on the site url.
 *
 * Search engines consider www.somedomain.com and somedomain.com to be two
 * different URLs when they both go to the same location. This SEO enhancement
 * prevents penalty for duplicate content by redirecting all incoming links to
 * one or the other.
 *
 * Prevents redirection for feeds, trackbacks, searches, comment popup, and
 * admin URLs. Does not redirect on non-pretty-permalink-supporting IIS 7+,
 * page/post previews, WP admin, Trackbacks, robots.txt, searches, or on POST
 * requests.
 *
 * Will also attempt to find the correct link when a user enters a URL that does
 * not exist based on exact WordPress query. Will instead try to parse the URL
 * or query in an attempt to figure the correct page to go to.
 *
 * @since 2.3.0
 * @uses $wp_rewrite
 * @uses $is_IIS
 *
 * @param string $requested_url Optional. The URL that was requested, used to
 *		figure if redirect is needed.
 * @param bool $do_redirect Optional. Redirect to the new URL.
 * @return null|false|string Null, if redirect not needed. False, if redirect
 *		not needed or the string of the URL
 */
function redirect_canonical($requested_url = null, $do_redirect = true)
{
    global $wp_rewrite, $is_IIS, $wp_query, $wpdb;
    if (isset($_SERVER['REQUEST_METHOD']) && !in_array(strtoupper($_SERVER['REQUEST_METHOD']), array('GET', 'HEAD'))) {
        return;
    }
    // If we're not in wp-admin and the post has been published and preview nonce
    // is non-existent or invalid then no need for preview in query
    if (is_preview() && get_query_var('p') && 'publish' == get_post_status(get_query_var('p'))) {
        if (!isset($_GET['preview_id']) || !isset($_GET['preview_nonce']) || !wp_verify_nonce($_GET['preview_nonce'], 'post_preview_' . (int) $_GET['preview_id'])) {
            $wp_query->is_preview = false;
        }
    }
    if (is_trackback() || is_search() || is_comments_popup() || is_admin() || is_preview() || is_robots() || $is_IIS && !iis7_supports_permalinks()) {
        return;
    }
    if (!$requested_url) {
        // build the URL in the address bar
        $requested_url = is_ssl() ? 'https://' : 'http://';
        $requested_url .= $_SERVER['HTTP_HOST'];
        $requested_url .= $_SERVER['REQUEST_URI'];
    }
    $original = @parse_url($requested_url);
    if (false === $original) {
        return;
    }
    // Some PHP setups turn requests for / into /index.php in REQUEST_URI
    // See: https://core.trac.wordpress.org/ticket/5017
    // See: https://core.trac.wordpress.org/ticket/7173
    // Disabled, for now:
    // $original['path'] = preg_replace('|/index\.php$|', '/', $original['path']);
    $redirect = $original;
    $redirect_url = false;
    // Notice fixing
    if (!isset($redirect['path'])) {
        $redirect['path'] = '';
    }
    if (!isset($redirect['query'])) {
        $redirect['query'] = '';
    }
    // If the original URL ended with non-breaking spaces, they were almost
    // certainly inserted by accident. Let's remove them, so the reader doesn't
    // see a 404 error with no obvious cause.
    $redirect['path'] = preg_replace('|(%C2%A0)+$|i', '', $redirect['path']);
    // It's not a preview, so remove it from URL
    if (get_query_var('preview')) {
        $redirect['query'] = remove_query_arg('preview', $redirect['query']);
    }
    if (is_feed() && $id = get_query_var('p')) {
        if ($redirect_url = get_post_comments_feed_link($id, get_query_var('feed'))) {
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type', 'feed'), $redirect_url);
            $redirect['path'] = parse_url($redirect_url, PHP_URL_PATH);
        }
    }
    if (is_singular() && 1 > $wp_query->post_count && $id = get_query_var('p')) {
        $vars = $wpdb->get_results($wpdb->prepare("SELECT post_type, post_parent FROM {$wpdb->posts} WHERE ID = %d", $id));
        if (isset($vars[0]) && $vars = $vars[0]) {
            if ('revision' == $vars->post_type && $vars->post_parent > 0) {
                $id = $vars->post_parent;
            }
            if ($redirect_url = get_permalink($id)) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    }
    // These tests give us a WP-generated permalink
    if (is_404()) {
        // Redirect ?page_id, ?p=, ?attachment_id= to their respective url's
        $id = max(get_query_var('p'), get_query_var('page_id'), get_query_var('attachment_id'));
        if ($id && $redirect_post = get_post($id)) {
            $post_type_obj = get_post_type_object($redirect_post->post_type);
            if ($post_type_obj->public) {
                $redirect_url = get_permalink($redirect_post);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
        if (get_query_var('day') && get_query_var('monthnum') && get_query_var('year')) {
            $year = get_query_var('year');
            $month = get_query_var('monthnum');
            $day = get_query_var('day');
            $date = sprintf('%04d-%02d-%02d', $year, $month, $day);
            if (!wp_checkdate($month, $day, $year, $date)) {
                $redirect_url = get_month_link($year, $month);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum', 'day'), $redirect_url);
            }
        } elseif (get_query_var('monthnum') && get_query_var('year') && 12 < get_query_var('monthnum')) {
            $redirect_url = get_year_link(get_query_var('year'));
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum'), $redirect_url);
        }
        if (!$redirect_url) {
            if ($redirect_url = redirect_guess_404_permalink()) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('page', 'feed', 'p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    } elseif (is_object($wp_rewrite) && $wp_rewrite->using_permalinks()) {
        // rewriting of old ?p=X, ?m=2004, ?m=200401, ?m=20040101
        if (is_attachment() && !empty($_GET['attachment_id']) && !$redirect_url) {
            if ($redirect_url = get_attachment_link(get_query_var('attachment_id'))) {
                $redirect['query'] = remove_query_arg('attachment_id', $redirect['query']);
            }
        } elseif (is_single() && !empty($_GET['p']) && !$redirect_url) {
            if ($redirect_url = get_permalink(get_query_var('p'))) {
                $redirect['query'] = remove_query_arg(array('p', 'post_type'), $redirect['query']);
            }
        } elseif (is_single() && !empty($_GET['name']) && !$redirect_url) {
            if ($redirect_url = get_permalink($wp_query->get_queried_object_id())) {
                $redirect['query'] = remove_query_arg('name', $redirect['query']);
            }
        } elseif (is_page() && !empty($_GET['page_id']) && !$redirect_url) {
            if ($redirect_url = get_permalink(get_query_var('page_id'))) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (is_page() && !is_feed() && isset($wp_query->queried_object) && 'page' == get_option('show_on_front') && $wp_query->queried_object->ID == get_option('page_on_front') && !$redirect_url) {
            $redirect_url = home_url('/');
        } elseif (is_home() && !empty($_GET['page_id']) && 'page' == get_option('show_on_front') && get_query_var('page_id') == get_option('page_for_posts') && !$redirect_url) {
            if ($redirect_url = get_permalink(get_option('page_for_posts'))) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (!empty($_GET['m']) && (is_year() || is_month() || is_day())) {
            $m = get_query_var('m');
            switch (strlen($m)) {
                case 4:
                    // Yearly
                    $redirect_url = get_year_link($m);
                    break;
                case 6:
                    // Monthly
                    $redirect_url = get_month_link(substr($m, 0, 4), substr($m, 4, 2));
                    break;
                case 8:
                    // Daily
                    $redirect_url = get_day_link(substr($m, 0, 4), substr($m, 4, 2), substr($m, 6, 2));
                    break;
            }
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('m', $redirect['query']);
            }
            // now moving on to non ?m=X year/month/day links
        } elseif (is_day() && get_query_var('year') && get_query_var('monthnum') && !empty($_GET['day'])) {
            if ($redirect_url = get_day_link(get_query_var('year'), get_query_var('monthnum'), get_query_var('day'))) {
                $redirect['query'] = remove_query_arg(array('year', 'monthnum', 'day'), $redirect['query']);
            }
        } elseif (is_month() && get_query_var('year') && !empty($_GET['monthnum'])) {
            if ($redirect_url = get_month_link(get_query_var('year'), get_query_var('monthnum'))) {
                $redirect['query'] = remove_query_arg(array('year', 'monthnum'), $redirect['query']);
            }
        } elseif (is_year() && !empty($_GET['year'])) {
            if ($redirect_url = get_year_link(get_query_var('year'))) {
                $redirect['query'] = remove_query_arg('year', $redirect['query']);
            }
        } elseif (is_author() && !empty($_GET['author']) && preg_match('|^[0-9]+$|', $_GET['author'])) {
            $author = get_userdata(get_query_var('author'));
            if (false !== $author && $wpdb->get_var($wpdb->prepare("SELECT ID FROM {$wpdb->posts} WHERE {$wpdb->posts}.post_author = %d AND {$wpdb->posts}.post_status = 'publish' LIMIT 1", $author->ID))) {
                if ($redirect_url = get_author_posts_url($author->ID, $author->user_nicename)) {
                    $redirect['query'] = remove_query_arg('author', $redirect['query']);
                }
            }
        } elseif (is_category() || is_tag() || is_tax()) {
            // Terms (Tags/categories)
            $term_count = 0;
            foreach ($wp_query->tax_query->queried_terms as $tax_query) {
                $term_count += count($tax_query['terms']);
            }
            $obj = $wp_query->get_queried_object();
            if ($term_count <= 1 && !empty($obj->term_id) && ($tax_url = get_term_link((int) $obj->term_id, $obj->taxonomy)) && !is_wp_error($tax_url)) {
                if (!empty($redirect['query'])) {
                    // Strip taxonomy query vars off the url.
                    $qv_remove = array('term', 'taxonomy');
                    if (is_category()) {
                        $qv_remove[] = 'category_name';
                        $qv_remove[] = 'cat';
                    } elseif (is_tag()) {
                        $qv_remove[] = 'tag';
                        $qv_remove[] = 'tag_id';
                    } else {
                        // Custom taxonomies will have a custom query var, remove those too:
                        $tax_obj = get_taxonomy($obj->taxonomy);
                        if (false !== $tax_obj->query_var) {
                            $qv_remove[] = $tax_obj->query_var;
                        }
                    }
                    $rewrite_vars = array_diff(array_keys($wp_query->query), array_keys($_GET));
                    if (!array_diff($rewrite_vars, array_keys($_GET))) {
                        // Check to see if all the Query vars are coming from the rewrite, none are set via $_GET
                        $redirect['query'] = remove_query_arg($qv_remove, $redirect['query']);
                        //Remove all of the per-tax qv's
                        // Create the destination url for this taxonomy
                        $tax_url = parse_url($tax_url);
                        if (!empty($tax_url['query'])) {
                            // Taxonomy accessible via ?taxonomy=..&term=.. or any custom qv..
                            parse_str($tax_url['query'], $query_vars);
                            $redirect['query'] = add_query_arg($query_vars, $redirect['query']);
                        } else {
                            // Taxonomy is accessible via a "pretty-URL"
                            $redirect['path'] = $tax_url['path'];
                        }
                    } else {
                        // Some query vars are set via $_GET. Unset those from $_GET that exist via the rewrite
                        foreach ($qv_remove as $_qv) {
                            if (isset($rewrite_vars[$_qv])) {
                                $redirect['query'] = remove_query_arg($_qv, $redirect['query']);
                            }
                        }
                    }
                }
            }
        } elseif (is_single() && strpos($wp_rewrite->permalink_structure, '%category%') !== false && $cat = get_query_var('category_name')) {
            $category = get_category_by_path($cat);
            $post_terms = wp_get_object_terms($wp_query->get_queried_object_id(), 'category', array('fields' => 'tt_ids'));
            if (!$category || is_wp_error($category) || !is_wp_error($post_terms) && !empty($post_terms) && !in_array($category->term_taxonomy_id, $post_terms)) {
                $redirect_url = get_permalink($wp_query->get_queried_object_id());
            }
        }
        // Post Paging
        if (is_singular() && !is_front_page() && get_query_var('page')) {
            if (!$redirect_url) {
                $redirect_url = get_permalink(get_queried_object_id());
            }
            $redirect_url = trailingslashit($redirect_url) . user_trailingslashit(get_query_var('page'), 'single_paged');
            $redirect['query'] = remove_query_arg('page', $redirect['query']);
        }
        // paging and feeds
        if (get_query_var('paged') || is_feed() || get_query_var('cpage')) {
            while (preg_match("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", $redirect['path']) || preg_match('#/(comments/?)?(feed|rss|rdf|atom|rss2)(/+)?$#', $redirect['path']) || preg_match("#/{$wp_rewrite->comments_pagination_base}-[0-9]+(/+)?\$#", $redirect['path'])) {
                // Strip off paging and feed
                $redirect['path'] = preg_replace("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", '/', $redirect['path']);
                // strip off any existing paging
                $redirect['path'] = preg_replace('#/(comments/?)?(feed|rss2?|rdf|atom)(/+|$)#', '/', $redirect['path']);
                // strip off feed endings
                $redirect['path'] = preg_replace("#/{$wp_rewrite->comments_pagination_base}-[0-9]+?(/+)?\$#", '/', $redirect['path']);
                // strip off any existing comment paging
            }
            $addl_path = '';
            if (is_feed() && in_array(get_query_var('feed'), $wp_rewrite->feeds)) {
                $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                if (!is_singular() && get_query_var('withcomments')) {
                    $addl_path .= 'comments/';
                }
                if ('rss' == get_default_feed() && 'feed' == get_query_var('feed') || 'rss' == get_query_var('feed')) {
                    $addl_path .= user_trailingslashit('feed/' . ((get_default_feed() == 'rss2') ? '' : 'rss2'), 'feed');
                } else {
                    $addl_path .= user_trailingslashit('feed/' . ((get_default_feed() == get_query_var('feed') || 'feed' == get_query_var('feed')) ? '' : get_query_var('feed')), 'feed');
                }
                $redirect['query'] = remove_query_arg('feed', $redirect['query']);
            } elseif (is_feed() && 'old' == get_query_var('feed')) {
                $old_feed_files = array('wp-atom.php' => 'atom', 'wp-commentsrss2.php' => 'comments_rss2', 'wp-feed.php' => get_default_feed(), 'wp-rdf.php' => 'rdf', 'wp-rss.php' => 'rss2', 'wp-rss2.php' => 'rss2');
                if (isset($old_feed_files[basename($redirect['path'])])) {
                    $redirect_url = get_feed_link($old_feed_files[basename($redirect['path'])]);
                    wp_redirect($redirect_url, 301);
                    die;
                }
            }
            if (get_query_var('paged') > 0) {
                $paged = get_query_var('paged');
                $redirect['query'] = remove_query_arg('paged', $redirect['query']);
                if (!is_feed()) {
                    if ($paged > 1 && !is_single()) {
                        $addl_path = ((!empty($addl_path)) ? trailingslashit($addl_path) : '') . user_trailingslashit("{$wp_rewrite->pagination_base}/{$paged}", 'paged');
                    } elseif (!is_single()) {
                        $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                    }
                } elseif ($paged > 1) {
                    $redirect['query'] = add_query_arg('paged', $paged, $redirect['query']);
                }
            }
            if (get_option('page_comments') && ('newest' == get_option('default_comments_page') && get_query_var('cpage') > 0 || 'newest' != get_option('default_comments_page') && get_query_var('cpage') > 1)) {
                $addl_path = ((!empty($addl_path)) ? trailingslashit($addl_path) : '') . user_trailingslashit($wp_rewrite->comments_pagination_base . '-' . get_query_var('cpage'), 'commentpaged');
                $redirect['query'] = remove_query_arg('cpage', $redirect['query']);
            }
            $redirect['path'] = user_trailingslashit(preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/?$|', '/', $redirect['path']));
            // strip off trailing /index.php/
            if (!empty($addl_path) && $wp_rewrite->using_index_permalinks() && strpos($redirect['path'], '/' . $wp_rewrite->index . '/') === false) {
                $redirect['path'] = trailingslashit($redirect['path']) . $wp_rewrite->index . '/';
            }
            if (!empty($addl_path)) {
                $redirect['path'] = trailingslashit($redirect['path']) . $addl_path;
            }
            $redirect_url = $redirect['scheme'] . '://' . $redirect['host'] . $redirect['path'];
        }
        if ('wp-register.php' == basename($redirect['path'])) {
            if (is_multisite()) {
                /** This filter is documented in wp-login.php */
                $redirect_url = apply_filters('wp_signup_location', network_site_url('wp-signup.php'));
            } else {
                $redirect_url = site_url('wp-login.php?action=register');
            }
            wp_redirect($redirect_url, 301);
            die;
        }
    }
    // tack on any additional query vars
    $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    if ($redirect_url && !empty($redirect['query'])) {
        parse_str($redirect['query'], $_parsed_query);
        $redirect = @parse_url($redirect_url);
        if (!empty($_parsed_query['name']) && !empty($redirect['query'])) {
            parse_str($redirect['query'], $_parsed_redirect_query);
            if (empty($_parsed_redirect_query['name'])) {
                unset($_parsed_query['name']);
            }
        }
        $_parsed_query = rawurlencode_deep($_parsed_query);
        $redirect_url = add_query_arg($_parsed_query, $redirect_url);
    }
    if ($redirect_url) {
        $redirect = @parse_url($redirect_url);
    }
    // www.example.com vs example.com
    $user_home = @parse_url(home_url());
    if (!empty($user_home['host'])) {
        $redirect['host'] = $user_home['host'];
    }
    if (empty($user_home['path'])) {
        $user_home['path'] = '/';
    }
    // Handle ports
    if (!empty($user_home['port'])) {
        $redirect['port'] = $user_home['port'];
    } else {
        unset($redirect['port']);
    }
    // trailing /index.php
    $redirect['path'] = preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/*?$|', '/', $redirect['path']);
    // Remove trailing spaces from the path
    $redirect['path'] = preg_replace('#(%20| )+$#', '', $redirect['path']);
    if (!empty($redirect['query'])) {
        // Remove trailing spaces from certain terminating query string args
        $redirect['query'] = preg_replace('#((p|page_id|cat|tag)=[^&]*?)(%20| )+$#', '$1', $redirect['query']);
        // Clean up empty query strings
        $redirect['query'] = trim(preg_replace('#(^|&)(p|page_id|cat|tag)=?(&|$)#', '&', $redirect['query']), '&');
        // Redirect obsolete feeds
        $redirect['query'] = preg_replace('#(^|&)feed=rss(&|$)#', '$1feed=rss2$2', $redirect['query']);
        // Remove redundant leading ampersands
        $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    }
    // strip /index.php/ when we're not using PATHINFO permalinks
    if (!$wp_rewrite->using_index_permalinks()) {
        $redirect['path'] = str_replace('/' . $wp_rewrite->index . '/', '/', $redirect['path']);
    }
    // trailing slashes
    if (is_object($wp_rewrite) && $wp_rewrite->using_permalinks() && !is_404() && (!is_front_page() || is_front_page() && get_query_var('paged') > 1)) {
        $user_ts_type = '';
        if (get_query_var('paged') > 0) {
            $user_ts_type = 'paged';
        } else {
            foreach (array('single', 'category', 'page', 'day', 'month', 'year', 'home') as $type) {
                $func = 'is_' . $type;
                if (call_user_func($func)) {
                    $user_ts_type = $type;
                    break;
                }
            }
        }
        $redirect['path'] = user_trailingslashit($redirect['path'], $user_ts_type);
    } elseif (is_front_page()) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Strip multiple slashes out of the URL
    if (strpos($redirect['path'], '//') > -1) {
        $redirect['path'] = preg_replace('|/+|', '/', $redirect['path']);
    }
    // Always trailing slash the Front Page URL
    if (trailingslashit($redirect['path']) == trailingslashit($user_home['path'])) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Ignore differences in host capitalization, as this can lead to infinite redirects
    // Only redirect no-www <=> yes-www
    if (strtolower($original['host']) == strtolower($redirect['host']) || strtolower($original['host']) != 'www.' . strtolower($redirect['host']) && 'www.' . strtolower($original['host']) != strtolower($redirect['host'])) {
        $redirect['host'] = $original['host'];
    }
    $compare_original = array($original['host'], $original['path']);
    if (!empty($original['port'])) {
        $compare_original[] = $original['port'];
    }
    if (!empty($original['query'])) {
        $compare_original[] = $original['query'];
    }
    $compare_redirect = array($redirect['host'], $redirect['path']);
    if (!empty($redirect['port'])) {
        $compare_redirect[] = $redirect['port'];
    }
    if (!empty($redirect['query'])) {
        $compare_redirect[] = $redirect['query'];
    }
    if ($compare_original !== $compare_redirect) {
        $redirect_url = $redirect['scheme'] . '://' . $redirect['host'];
        if (!empty($redirect['port'])) {
            $redirect_url .= ':' . $redirect['port'];
        }
        $redirect_url .= $redirect['path'];
        if (!empty($redirect['query'])) {
            $redirect_url .= '?' . $redirect['query'];
        }
    }
    if (!$redirect_url || $redirect_url == $requested_url) {
        return false;
    }
    // Hex encoded octets are case-insensitive.
    if (false !== strpos($requested_url, '%')) {
        if (!function_exists('lowercase_octets')) {
            function lowercase_octets($matches)
            {
                return strtolower($matches[0]);
            }
        }
        $requested_url = preg_replace_callback('|%[a-fA-F0-9][a-fA-F0-9]|', 'lowercase_octets', $requested_url);
    }
    /**
     * Filter the canonical redirect URL.
     *
     * Returning false to this filter will cancel the redirect.
     *
     * @since 2.3.0
     *
     * @param string $redirect_url  The redirect URL.
     * @param string $requested_url The requested URL.
     */
    $redirect_url = apply_filters('redirect_canonical', $redirect_url, $requested_url);
    if (!$redirect_url || $redirect_url == $requested_url) {
        // yes, again -- in case the filter aborted the request
        return false;
    }
    if ($do_redirect) {
        // protect against chained redirects
        if (!redirect_canonical($redirect_url, false)) {
            wp_redirect($redirect_url, 301);
            exit;
        } else {
            // Debug
            // die("1: $redirect_url<br />2: " . redirect_canonical( $redirect_url, false ) );
            return false;
        }
    } else {
        return $redirect_url;
    }
}

WordPress Version: 4.1

/**
 * Canonical API to handle WordPress Redirecting
 *
 * Based on "Permalink Redirect" from Scott Yang and "Enforce www. Preference"
 * by Mark Jaquith
 *
 * @package WordPress
 * @since 2.3.0
 */
/**
 * Redirects incoming links to the proper URL based on the site url.
 *
 * Search engines consider www.somedomain.com and somedomain.com to be two
 * different URLs when they both go to the same location. This SEO enhancement
 * prevents penalty for duplicate content by redirecting all incoming links to
 * one or the other.
 *
 * Prevents redirection for feeds, trackbacks, searches, comment popup, and
 * admin URLs. Does not redirect on non-pretty-permalink-supporting IIS 7+,
 * page/post previews, WP admin, Trackbacks, robots.txt, searches, or on POST
 * requests.
 *
 * Will also attempt to find the correct link when a user enters a URL that does
 * not exist based on exact WordPress query. Will instead try to parse the URL
 * or query in an attempt to figure the correct page to go to.
 *
 * @since 2.3.0
 * @uses $wp_rewrite
 * @uses $is_IIS
 *
 * @param string $requested_url Optional. The URL that was requested, used to
 *		figure if redirect is needed.
 * @param bool $do_redirect Optional. Redirect to the new URL.
 * @return null|false|string Null, if redirect not needed. False, if redirect
 *		not needed or the string of the URL
 */
function redirect_canonical($requested_url = null, $do_redirect = true)
{
    global $wp_rewrite, $is_IIS, $wp_query, $wpdb;
    if (isset($_SERVER['REQUEST_METHOD']) && !in_array(strtoupper($_SERVER['REQUEST_METHOD']), array('GET', 'HEAD'))) {
        return;
    }
    // If we're not in wp-admin and the post has been published and preview nonce
    // is non-existent or invalid then no need for preview in query
    if (is_preview() && get_query_var('p') && 'publish' == get_post_status(get_query_var('p'))) {
        if (!isset($_GET['preview_id']) || !isset($_GET['preview_nonce']) || !wp_verify_nonce($_GET['preview_nonce'], 'post_preview_' . (int) $_GET['preview_id'])) {
            $wp_query->is_preview = false;
        }
    }
    if (is_trackback() || is_search() || is_comments_popup() || is_admin() || is_preview() || is_robots() || $is_IIS && !iis7_supports_permalinks()) {
        return;
    }
    if (!$requested_url) {
        // build the URL in the address bar
        $requested_url = is_ssl() ? 'https://' : 'http://';
        $requested_url .= $_SERVER['HTTP_HOST'];
        $requested_url .= $_SERVER['REQUEST_URI'];
    }
    $original = @parse_url($requested_url);
    if (false === $original) {
        return;
    }
    // Some PHP setups turn requests for / into /index.php in REQUEST_URI
    // See: https://core.trac.wordpress.org/ticket/5017
    // See: https://core.trac.wordpress.org/ticket/7173
    // Disabled, for now:
    // $original['path'] = preg_replace('|/index\.php$|', '/', $original['path']);
    $redirect = $original;
    $redirect_url = false;
    // Notice fixing
    if (!isset($redirect['path'])) {
        $redirect['path'] = '';
    }
    if (!isset($redirect['query'])) {
        $redirect['query'] = '';
    }
    // It's not a preview, so remove it from URL
    if (get_query_var('preview')) {
        $redirect['query'] = remove_query_arg('preview', $redirect['query']);
    }
    if (is_feed() && $id = get_query_var('p')) {
        if ($redirect_url = get_post_comments_feed_link($id, get_query_var('feed'))) {
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type', 'feed'), $redirect_url);
            $redirect['path'] = parse_url($redirect_url, PHP_URL_PATH);
        }
    }
    if (is_singular() && 1 > $wp_query->post_count && $id = get_query_var('p')) {
        $vars = $wpdb->get_results($wpdb->prepare("SELECT post_type, post_parent FROM {$wpdb->posts} WHERE ID = %d", $id));
        if (isset($vars[0]) && $vars = $vars[0]) {
            if ('revision' == $vars->post_type && $vars->post_parent > 0) {
                $id = $vars->post_parent;
            }
            if ($redirect_url = get_permalink($id)) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    }
    // These tests give us a WP-generated permalink
    if (is_404()) {
        // Redirect ?page_id, ?p=, ?attachment_id= to their respective url's
        $id = max(get_query_var('p'), get_query_var('page_id'), get_query_var('attachment_id'));
        if ($id && $redirect_post = get_post($id)) {
            $post_type_obj = get_post_type_object($redirect_post->post_type);
            if ($post_type_obj->public) {
                $redirect_url = get_permalink($redirect_post);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
        if (get_query_var('day') && get_query_var('monthnum') && get_query_var('year')) {
            $year = get_query_var('year');
            $month = get_query_var('monthnum');
            $day = get_query_var('day');
            $date = sprintf('%04d-%02d-%02d', $year, $month, $day);
            if (!wp_checkdate($month, $day, $year, $date)) {
                $redirect_url = get_month_link($year, $month);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum', 'day'), $redirect_url);
            }
        } elseif (get_query_var('monthnum') && get_query_var('year') && 12 < get_query_var('monthnum')) {
            $redirect_url = get_year_link(get_query_var('year'));
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum'), $redirect_url);
        }
        if (!$redirect_url) {
            if ($redirect_url = redirect_guess_404_permalink()) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('page', 'feed', 'p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    } elseif (is_object($wp_rewrite) && $wp_rewrite->using_permalinks()) {
        // rewriting of old ?p=X, ?m=2004, ?m=200401, ?m=20040101
        if (is_attachment() && !empty($_GET['attachment_id']) && !$redirect_url) {
            if ($redirect_url = get_attachment_link(get_query_var('attachment_id'))) {
                $redirect['query'] = remove_query_arg('attachment_id', $redirect['query']);
            }
        } elseif (is_single() && !empty($_GET['p']) && !$redirect_url) {
            if ($redirect_url = get_permalink(get_query_var('p'))) {
                $redirect['query'] = remove_query_arg(array('p', 'post_type'), $redirect['query']);
            }
        } elseif (is_single() && !empty($_GET['name']) && !$redirect_url) {
            if ($redirect_url = get_permalink($wp_query->get_queried_object_id())) {
                $redirect['query'] = remove_query_arg('name', $redirect['query']);
            }
        } elseif (is_page() && !empty($_GET['page_id']) && !$redirect_url) {
            if ($redirect_url = get_permalink(get_query_var('page_id'))) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (is_page() && !is_feed() && isset($wp_query->queried_object) && 'page' == get_option('show_on_front') && $wp_query->queried_object->ID == get_option('page_on_front') && !$redirect_url) {
            $redirect_url = home_url('/');
        } elseif (is_home() && !empty($_GET['page_id']) && 'page' == get_option('show_on_front') && get_query_var('page_id') == get_option('page_for_posts') && !$redirect_url) {
            if ($redirect_url = get_permalink(get_option('page_for_posts'))) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (!empty($_GET['m']) && (is_year() || is_month() || is_day())) {
            $m = get_query_var('m');
            switch (strlen($m)) {
                case 4:
                    // Yearly
                    $redirect_url = get_year_link($m);
                    break;
                case 6:
                    // Monthly
                    $redirect_url = get_month_link(substr($m, 0, 4), substr($m, 4, 2));
                    break;
                case 8:
                    // Daily
                    $redirect_url = get_day_link(substr($m, 0, 4), substr($m, 4, 2), substr($m, 6, 2));
                    break;
            }
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('m', $redirect['query']);
            }
            // now moving on to non ?m=X year/month/day links
        } elseif (is_day() && get_query_var('year') && get_query_var('monthnum') && !empty($_GET['day'])) {
            if ($redirect_url = get_day_link(get_query_var('year'), get_query_var('monthnum'), get_query_var('day'))) {
                $redirect['query'] = remove_query_arg(array('year', 'monthnum', 'day'), $redirect['query']);
            }
        } elseif (is_month() && get_query_var('year') && !empty($_GET['monthnum'])) {
            if ($redirect_url = get_month_link(get_query_var('year'), get_query_var('monthnum'))) {
                $redirect['query'] = remove_query_arg(array('year', 'monthnum'), $redirect['query']);
            }
        } elseif (is_year() && !empty($_GET['year'])) {
            if ($redirect_url = get_year_link(get_query_var('year'))) {
                $redirect['query'] = remove_query_arg('year', $redirect['query']);
            }
        } elseif (is_author() && !empty($_GET['author']) && preg_match('|^[0-9]+$|', $_GET['author'])) {
            $author = get_userdata(get_query_var('author'));
            if (false !== $author && $wpdb->get_var($wpdb->prepare("SELECT ID FROM {$wpdb->posts} WHERE {$wpdb->posts}.post_author = %d AND {$wpdb->posts}.post_status = 'publish' LIMIT 1", $author->ID))) {
                if ($redirect_url = get_author_posts_url($author->ID, $author->user_nicename)) {
                    $redirect['query'] = remove_query_arg('author', $redirect['query']);
                }
            }
        } elseif (is_category() || is_tag() || is_tax()) {
            // Terms (Tags/categories)
            $term_count = 0;
            foreach ($wp_query->tax_query->queried_terms as $tax_query) {
                $term_count += count($tax_query['terms']);
            }
            $obj = $wp_query->get_queried_object();
            if ($term_count <= 1 && !empty($obj->term_id) && ($tax_url = get_term_link((int) $obj->term_id, $obj->taxonomy)) && !is_wp_error($tax_url)) {
                if (!empty($redirect['query'])) {
                    // Strip taxonomy query vars off the url.
                    $qv_remove = array('term', 'taxonomy');
                    if (is_category()) {
                        $qv_remove[] = 'category_name';
                        $qv_remove[] = 'cat';
                    } elseif (is_tag()) {
                        $qv_remove[] = 'tag';
                        $qv_remove[] = 'tag_id';
                    } else {
                        // Custom taxonomies will have a custom query var, remove those too:
                        $tax_obj = get_taxonomy($obj->taxonomy);
                        if (false !== $tax_obj->query_var) {
                            $qv_remove[] = $tax_obj->query_var;
                        }
                    }
                    $rewrite_vars = array_diff(array_keys($wp_query->query), array_keys($_GET));
                    if (!array_diff($rewrite_vars, array_keys($_GET))) {
                        // Check to see if all the Query vars are coming from the rewrite, none are set via $_GET
                        $redirect['query'] = remove_query_arg($qv_remove, $redirect['query']);
                        //Remove all of the per-tax qv's
                        // Create the destination url for this taxonomy
                        $tax_url = parse_url($tax_url);
                        if (!empty($tax_url['query'])) {
                            // Taxonomy accessible via ?taxonomy=..&term=.. or any custom qv..
                            parse_str($tax_url['query'], $query_vars);
                            $redirect['query'] = add_query_arg($query_vars, $redirect['query']);
                        } else {
                            // Taxonomy is accessible via a "pretty-URL"
                            $redirect['path'] = $tax_url['path'];
                        }
                    } else {
                        // Some query vars are set via $_GET. Unset those from $_GET that exist via the rewrite
                        foreach ($qv_remove as $_qv) {
                            if (isset($rewrite_vars[$_qv])) {
                                $redirect['query'] = remove_query_arg($_qv, $redirect['query']);
                            }
                        }
                    }
                }
            }
        } elseif (is_single() && strpos($wp_rewrite->permalink_structure, '%category%') !== false && $cat = get_query_var('category_name')) {
            $category = get_category_by_path($cat);
            $post_terms = wp_get_object_terms($wp_query->get_queried_object_id(), 'category', array('fields' => 'tt_ids'));
            if (!$category || is_wp_error($category) || !is_wp_error($post_terms) && !empty($post_terms) && !in_array($category->term_taxonomy_id, $post_terms)) {
                $redirect_url = get_permalink($wp_query->get_queried_object_id());
            }
        }
        // Post Paging
        if (is_singular() && !is_front_page() && get_query_var('page')) {
            if (!$redirect_url) {
                $redirect_url = get_permalink(get_queried_object_id());
            }
            $redirect_url = trailingslashit($redirect_url) . user_trailingslashit(get_query_var('page'), 'single_paged');
            $redirect['query'] = remove_query_arg('page', $redirect['query']);
        }
        // paging and feeds
        if (get_query_var('paged') || is_feed() || get_query_var('cpage')) {
            while (preg_match("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", $redirect['path']) || preg_match('#/(comments/?)?(feed|rss|rdf|atom|rss2)(/+)?$#', $redirect['path']) || preg_match('#/comment-page-[0-9]+(/+)?$#', $redirect['path'])) {
                // Strip off paging and feed
                $redirect['path'] = preg_replace("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", '/', $redirect['path']);
                // strip off any existing paging
                $redirect['path'] = preg_replace('#/(comments/?)?(feed|rss2?|rdf|atom)(/+|$)#', '/', $redirect['path']);
                // strip off feed endings
                $redirect['path'] = preg_replace('#/comment-page-[0-9]+?(/+)?$#', '/', $redirect['path']);
                // strip off any existing comment paging
            }
            $addl_path = '';
            if (is_feed() && in_array(get_query_var('feed'), $wp_rewrite->feeds)) {
                $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                if (!is_singular() && get_query_var('withcomments')) {
                    $addl_path .= 'comments/';
                }
                if ('rss' == get_default_feed() && 'feed' == get_query_var('feed') || 'rss' == get_query_var('feed')) {
                    $addl_path .= user_trailingslashit('feed/' . ((get_default_feed() == 'rss2') ? '' : 'rss2'), 'feed');
                } else {
                    $addl_path .= user_trailingslashit('feed/' . ((get_default_feed() == get_query_var('feed') || 'feed' == get_query_var('feed')) ? '' : get_query_var('feed')), 'feed');
                }
                $redirect['query'] = remove_query_arg('feed', $redirect['query']);
            } elseif (is_feed() && 'old' == get_query_var('feed')) {
                $old_feed_files = array('wp-atom.php' => 'atom', 'wp-commentsrss2.php' => 'comments_rss2', 'wp-feed.php' => get_default_feed(), 'wp-rdf.php' => 'rdf', 'wp-rss.php' => 'rss2', 'wp-rss2.php' => 'rss2');
                if (isset($old_feed_files[basename($redirect['path'])])) {
                    $redirect_url = get_feed_link($old_feed_files[basename($redirect['path'])]);
                    wp_redirect($redirect_url, 301);
                    die;
                }
            }
            if (get_query_var('paged') > 0) {
                $paged = get_query_var('paged');
                $redirect['query'] = remove_query_arg('paged', $redirect['query']);
                if (!is_feed()) {
                    if ($paged > 1 && !is_single()) {
                        $addl_path = ((!empty($addl_path)) ? trailingslashit($addl_path) : '') . user_trailingslashit("{$wp_rewrite->pagination_base}/{$paged}", 'paged');
                    } elseif (!is_single()) {
                        $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                    }
                } elseif ($paged > 1) {
                    $redirect['query'] = add_query_arg('paged', $paged, $redirect['query']);
                }
            }
            if (get_option('page_comments') && ('newest' == get_option('default_comments_page') && get_query_var('cpage') > 0 || 'newest' != get_option('default_comments_page') && get_query_var('cpage') > 1)) {
                $addl_path = ((!empty($addl_path)) ? trailingslashit($addl_path) : '') . user_trailingslashit('comment-page-' . get_query_var('cpage'), 'commentpaged');
                $redirect['query'] = remove_query_arg('cpage', $redirect['query']);
            }
            $redirect['path'] = user_trailingslashit(preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/?$|', '/', $redirect['path']));
            // strip off trailing /index.php/
            if (!empty($addl_path) && $wp_rewrite->using_index_permalinks() && strpos($redirect['path'], '/' . $wp_rewrite->index . '/') === false) {
                $redirect['path'] = trailingslashit($redirect['path']) . $wp_rewrite->index . '/';
            }
            if (!empty($addl_path)) {
                $redirect['path'] = trailingslashit($redirect['path']) . $addl_path;
            }
            $redirect_url = $redirect['scheme'] . '://' . $redirect['host'] . $redirect['path'];
        }
        if ('wp-register.php' == basename($redirect['path'])) {
            if (is_multisite()) {
                /** This filter is documented in wp-login.php */
                $redirect_url = apply_filters('wp_signup_location', network_site_url('wp-signup.php'));
            } else {
                $redirect_url = site_url('wp-login.php?action=register');
            }
            wp_redirect($redirect_url, 301);
            die;
        }
    }
    // tack on any additional query vars
    $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    if ($redirect_url && !empty($redirect['query'])) {
        parse_str($redirect['query'], $_parsed_query);
        $redirect = @parse_url($redirect_url);
        if (!empty($_parsed_query['name']) && !empty($redirect['query'])) {
            parse_str($redirect['query'], $_parsed_redirect_query);
            if (empty($_parsed_redirect_query['name'])) {
                unset($_parsed_query['name']);
            }
        }
        $_parsed_query = rawurlencode_deep($_parsed_query);
        $redirect_url = add_query_arg($_parsed_query, $redirect_url);
    }
    if ($redirect_url) {
        $redirect = @parse_url($redirect_url);
    }
    // www.example.com vs example.com
    $user_home = @parse_url(home_url());
    if (!empty($user_home['host'])) {
        $redirect['host'] = $user_home['host'];
    }
    if (empty($user_home['path'])) {
        $user_home['path'] = '/';
    }
    // Handle ports
    if (!empty($user_home['port'])) {
        $redirect['port'] = $user_home['port'];
    } else {
        unset($redirect['port']);
    }
    // trailing /index.php
    $redirect['path'] = preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/*?$|', '/', $redirect['path']);
    // Remove trailing spaces from the path
    $redirect['path'] = preg_replace('#(%20| )+$#', '', $redirect['path']);
    if (!empty($redirect['query'])) {
        // Remove trailing spaces from certain terminating query string args
        $redirect['query'] = preg_replace('#((p|page_id|cat|tag)=[^&]*?)(%20| )+$#', '$1', $redirect['query']);
        // Clean up empty query strings
        $redirect['query'] = trim(preg_replace('#(^|&)(p|page_id|cat|tag)=?(&|$)#', '&', $redirect['query']), '&');
        // Redirect obsolete feeds
        $redirect['query'] = preg_replace('#(^|&)feed=rss(&|$)#', '$1feed=rss2$2', $redirect['query']);
        // Remove redundant leading ampersands
        $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    }
    // strip /index.php/ when we're not using PATHINFO permalinks
    if (!$wp_rewrite->using_index_permalinks()) {
        $redirect['path'] = str_replace('/' . $wp_rewrite->index . '/', '/', $redirect['path']);
    }
    // trailing slashes
    if (is_object($wp_rewrite) && $wp_rewrite->using_permalinks() && !is_404() && (!is_front_page() || is_front_page() && get_query_var('paged') > 1)) {
        $user_ts_type = '';
        if (get_query_var('paged') > 0) {
            $user_ts_type = 'paged';
        } else {
            foreach (array('single', 'category', 'page', 'day', 'month', 'year', 'home') as $type) {
                $func = 'is_' . $type;
                if (call_user_func($func)) {
                    $user_ts_type = $type;
                    break;
                }
            }
        }
        $redirect['path'] = user_trailingslashit($redirect['path'], $user_ts_type);
    } elseif (is_front_page()) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Strip multiple slashes out of the URL
    if (strpos($redirect['path'], '//') > -1) {
        $redirect['path'] = preg_replace('|/+|', '/', $redirect['path']);
    }
    // Always trailing slash the Front Page URL
    if (trailingslashit($redirect['path']) == trailingslashit($user_home['path'])) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Ignore differences in host capitalization, as this can lead to infinite redirects
    // Only redirect no-www <=> yes-www
    if (strtolower($original['host']) == strtolower($redirect['host']) || strtolower($original['host']) != 'www.' . strtolower($redirect['host']) && 'www.' . strtolower($original['host']) != strtolower($redirect['host'])) {
        $redirect['host'] = $original['host'];
    }
    $compare_original = array($original['host'], $original['path']);
    if (!empty($original['port'])) {
        $compare_original[] = $original['port'];
    }
    if (!empty($original['query'])) {
        $compare_original[] = $original['query'];
    }
    $compare_redirect = array($redirect['host'], $redirect['path']);
    if (!empty($redirect['port'])) {
        $compare_redirect[] = $redirect['port'];
    }
    if (!empty($redirect['query'])) {
        $compare_redirect[] = $redirect['query'];
    }
    if ($compare_original !== $compare_redirect) {
        $redirect_url = $redirect['scheme'] . '://' . $redirect['host'];
        if (!empty($redirect['port'])) {
            $redirect_url .= ':' . $redirect['port'];
        }
        $redirect_url .= $redirect['path'];
        if (!empty($redirect['query'])) {
            $redirect_url .= '?' . $redirect['query'];
        }
    }
    if (!$redirect_url || $redirect_url == $requested_url) {
        return false;
    }
    // Hex encoded octets are case-insensitive.
    if (false !== strpos($requested_url, '%')) {
        if (!function_exists('lowercase_octets')) {
            function lowercase_octets($matches)
            {
                return strtolower($matches[0]);
            }
        }
        $requested_url = preg_replace_callback('|%[a-fA-F0-9][a-fA-F0-9]|', 'lowercase_octets', $requested_url);
    }
    /**
     * Filter the canonical redirect URL.
     *
     * Returning false to this filter will cancel the redirect.
     *
     * @since 2.3.0
     *
     * @param string $redirect_url  The redirect URL.
     * @param string $requested_url The requested URL.
     */
    $redirect_url = apply_filters('redirect_canonical', $redirect_url, $requested_url);
    if (!$redirect_url || $redirect_url == $requested_url) {
        // yes, again -- in case the filter aborted the request
        return false;
    }
    if ($do_redirect) {
        // protect against chained redirects
        if (!redirect_canonical($redirect_url, false)) {
            wp_redirect($redirect_url, 301);
            exit;
        } else {
            // Debug
            // die("1: $redirect_url<br />2: " . redirect_canonical( $redirect_url, false ) );
            return false;
        }
    } else {
        return $redirect_url;
    }
}

WordPress Version: 0.1

/**
 * Canonical API to handle WordPress Redirecting
 *
 * Based on "Permalink Redirect" from Scott Yang and "Enforce www. Preference"
 * by Mark Jaquith
 *
 * @package WordPress
 * @since 2.3.0
 */
/**
 * Redirects incoming links to the proper URL based on the site url.
 *
 * Search engines consider www.somedomain.com and somedomain.com to be two
 * different URLs when they both go to the same location. This SEO enhancement
 * prevents penalty for duplicate content by redirecting all incoming links to
 * one or the other.
 *
 * Prevents redirection for feeds, trackbacks, searches, comment popup, and
 * admin URLs. Does not redirect on non-pretty-permalink-supporting IIS 7+,
 * page/post previews, WP admin, Trackbacks, robots.txt, searches, or on POST
 * requests.
 *
 * Will also attempt to find the correct link when a user enters a URL that does
 * not exist based on exact WordPress query. Will instead try to parse the URL
 * or query in an attempt to figure the correct page to go to.
 *
 * @since 2.3.0
 * @uses $wp_rewrite
 * @uses $is_IIS
 *
 * @param string $requested_url Optional. The URL that was requested, used to
 *		figure if redirect is needed.
 * @param bool $do_redirect Optional. Redirect to the new URL.
 * @return null|false|string Null, if redirect not needed. False, if redirect
 *		not needed or the string of the URL
 */
function redirect_canonical($requested_url = null, $do_redirect = true)
{
    global $wp_rewrite, $is_IIS, $wp_query, $wpdb;
    if (isset($_SERVER['REQUEST_METHOD']) && !in_array(strtoupper($_SERVER['REQUEST_METHOD']), array('GET', 'HEAD'))) {
        return;
    }
    // If we're not in wp-admin and the post has been published and preview nonce
    // is non-existent or invalid then no need for preview in query
    if (is_preview() && get_query_var('p') && 'publish' == get_post_status(get_query_var('p'))) {
        if (!isset($_GET['preview_id']) || !isset($_GET['preview_nonce']) || !wp_verify_nonce($_GET['preview_nonce'], 'post_preview_' . (int) $_GET['preview_id'])) {
            $wp_query->is_preview = false;
        }
    }
    if (is_trackback() || is_search() || is_comments_popup() || is_admin() || is_preview() || is_robots() || $is_IIS && !iis7_supports_permalinks()) {
        return;
    }
    if (!$requested_url) {
        // build the URL in the address bar
        $requested_url = is_ssl() ? 'https://' : 'http://';
        $requested_url .= $_SERVER['HTTP_HOST'];
        $requested_url .= $_SERVER['REQUEST_URI'];
    }
    $original = @parse_url($requested_url);
    if (false === $original) {
        return;
    }
    // Some PHP setups turn requests for / into /index.php in REQUEST_URI
    // See: http://trac.wordpress.org/ticket/5017
    // See: http://trac.wordpress.org/ticket/7173
    // Disabled, for now:
    // $original['path'] = preg_replace('|/index\.php$|', '/', $original['path']);
    $redirect = $original;
    $redirect_url = false;
    // Notice fixing
    if (!isset($redirect['path'])) {
        $redirect['path'] = '';
    }
    if (!isset($redirect['query'])) {
        $redirect['query'] = '';
    }
    // It's not a preview, so remove it from URL
    if (get_query_var('preview')) {
        $redirect['query'] = remove_query_arg('preview', $redirect['query']);
    }
    if (is_feed() && $id = get_query_var('p')) {
        if ($redirect_url = get_post_comments_feed_link($id, get_query_var('feed'))) {
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type', 'feed'), $redirect_url);
            $redirect['path'] = parse_url($redirect_url, PHP_URL_PATH);
        }
    }
    if (is_singular() && 1 > $wp_query->post_count && $id = get_query_var('p')) {
        $vars = $wpdb->get_results($wpdb->prepare("SELECT post_type, post_parent FROM {$wpdb->posts} WHERE ID = %d", $id));
        if (isset($vars[0]) && $vars = $vars[0]) {
            if ('revision' == $vars->post_type && $vars->post_parent > 0) {
                $id = $vars->post_parent;
            }
            if ($redirect_url = get_permalink($id)) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    }
    // These tests give us a WP-generated permalink
    if (is_404()) {
        // Redirect ?page_id, ?p=, ?attachment_id= to their respective url's
        $id = max(get_query_var('p'), get_query_var('page_id'), get_query_var('attachment_id'));
        if ($id && $redirect_post = get_post($id)) {
            $post_type_obj = get_post_type_object($redirect_post->post_type);
            if ($post_type_obj->public) {
                $redirect_url = get_permalink($redirect_post);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
        if (get_query_var('day') && get_query_var('monthnum') && get_query_var('year')) {
            $year = get_query_var('year');
            $month = get_query_var('monthnum');
            $day = get_query_var('day');
            $date = sprintf('%04d-%02d-%02d', $year, $month, $day);
            if (!wp_checkdate($month, $day, $year, $date)) {
                $redirect_url = get_month_link($year, $month);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum', 'day'), $redirect_url);
            }
        } elseif (get_query_var('monthnum') && get_query_var('year') && 12 < get_query_var('monthnum')) {
            $redirect_url = get_year_link(get_query_var('year'));
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum'), $redirect_url);
        }
        if (!$redirect_url) {
            if ($redirect_url = redirect_guess_404_permalink()) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('page', 'feed', 'p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    } elseif (is_object($wp_rewrite) && $wp_rewrite->using_permalinks()) {
        // rewriting of old ?p=X, ?m=2004, ?m=200401, ?m=20040101
        if (is_attachment() && !empty($_GET['attachment_id']) && !$redirect_url) {
            if ($redirect_url = get_attachment_link(get_query_var('attachment_id'))) {
                $redirect['query'] = remove_query_arg('attachment_id', $redirect['query']);
            }
        } elseif (is_single() && !empty($_GET['p']) && !$redirect_url) {
            if ($redirect_url = get_permalink(get_query_var('p'))) {
                $redirect['query'] = remove_query_arg(array('p', 'post_type'), $redirect['query']);
            }
        } elseif (is_single() && !empty($_GET['name']) && !$redirect_url) {
            if ($redirect_url = get_permalink($wp_query->get_queried_object_id())) {
                $redirect['query'] = remove_query_arg('name', $redirect['query']);
            }
        } elseif (is_page() && !empty($_GET['page_id']) && !$redirect_url) {
            if ($redirect_url = get_permalink(get_query_var('page_id'))) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (is_page() && !is_feed() && isset($wp_query->queried_object) && 'page' == get_option('show_on_front') && $wp_query->queried_object->ID == get_option('page_on_front') && !$redirect_url) {
            $redirect_url = home_url('/');
        } elseif (is_home() && !empty($_GET['page_id']) && 'page' == get_option('show_on_front') && get_query_var('page_id') == get_option('page_for_posts') && !$redirect_url) {
            if ($redirect_url = get_permalink(get_option('page_for_posts'))) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (!empty($_GET['m']) && (is_year() || is_month() || is_day())) {
            $m = get_query_var('m');
            switch (strlen($m)) {
                case 4:
                    // Yearly
                    $redirect_url = get_year_link($m);
                    break;
                case 6:
                    // Monthly
                    $redirect_url = get_month_link(substr($m, 0, 4), substr($m, 4, 2));
                    break;
                case 8:
                    // Daily
                    $redirect_url = get_day_link(substr($m, 0, 4), substr($m, 4, 2), substr($m, 6, 2));
                    break;
            }
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('m', $redirect['query']);
            }
            // now moving on to non ?m=X year/month/day links
        } elseif (is_day() && get_query_var('year') && get_query_var('monthnum') && !empty($_GET['day'])) {
            if ($redirect_url = get_day_link(get_query_var('year'), get_query_var('monthnum'), get_query_var('day'))) {
                $redirect['query'] = remove_query_arg(array('year', 'monthnum', 'day'), $redirect['query']);
            }
        } elseif (is_month() && get_query_var('year') && !empty($_GET['monthnum'])) {
            if ($redirect_url = get_month_link(get_query_var('year'), get_query_var('monthnum'))) {
                $redirect['query'] = remove_query_arg(array('year', 'monthnum'), $redirect['query']);
            }
        } elseif (is_year() && !empty($_GET['year'])) {
            if ($redirect_url = get_year_link(get_query_var('year'))) {
                $redirect['query'] = remove_query_arg('year', $redirect['query']);
            }
        } elseif (is_author() && !empty($_GET['author']) && preg_match('|^[0-9]+$|', $_GET['author'])) {
            $author = get_userdata(get_query_var('author'));
            if (false !== $author && $wpdb->get_var($wpdb->prepare("SELECT ID FROM {$wpdb->posts} WHERE {$wpdb->posts}.post_author = %d AND {$wpdb->posts}.post_status = 'publish' LIMIT 1", $author->ID))) {
                if ($redirect_url = get_author_posts_url($author->ID, $author->user_nicename)) {
                    $redirect['query'] = remove_query_arg('author', $redirect['query']);
                }
            }
        } elseif (is_category() || is_tag() || is_tax()) {
            // Terms (Tags/categories)
            $term_count = 0;
            foreach ($wp_query->tax_query->queries as $tax_query) {
                $term_count += count($tax_query['terms']);
            }
            $obj = $wp_query->get_queried_object();
            if ($term_count <= 1 && !empty($obj->term_id) && ($tax_url = get_term_link((int) $obj->term_id, $obj->taxonomy)) && !is_wp_error($tax_url)) {
                if (!empty($redirect['query'])) {
                    // Strip taxonomy query vars off the url.
                    $qv_remove = array('term', 'taxonomy');
                    if (is_category()) {
                        $qv_remove[] = 'category_name';
                        $qv_remove[] = 'cat';
                    } elseif (is_tag()) {
                        $qv_remove[] = 'tag';
                        $qv_remove[] = 'tag_id';
                    } else {
                        // Custom taxonomies will have a custom query var, remove those too:
                        $tax_obj = get_taxonomy($obj->taxonomy);
                        if (false !== $tax_obj->query_var) {
                            $qv_remove[] = $tax_obj->query_var;
                        }
                    }
                    $rewrite_vars = array_diff(array_keys($wp_query->query), array_keys($_GET));
                    if (!array_diff($rewrite_vars, array_keys($_GET))) {
                        // Check to see if all the Query vars are coming from the rewrite, none are set via $_GET
                        $redirect['query'] = remove_query_arg($qv_remove, $redirect['query']);
                        //Remove all of the per-tax qv's
                        // Create the destination url for this taxonomy
                        $tax_url = parse_url($tax_url);
                        if (!empty($tax_url['query'])) {
                            // Taxonomy accessible via ?taxonomy=..&term=.. or any custom qv..
                            parse_str($tax_url['query'], $query_vars);
                            $redirect['query'] = add_query_arg($query_vars, $redirect['query']);
                        } else {
                            // Taxonomy is accessible via a "pretty-URL"
                            $redirect['path'] = $tax_url['path'];
                        }
                    } else {
                        // Some query vars are set via $_GET. Unset those from $_GET that exist via the rewrite
                        foreach ($qv_remove as $_qv) {
                            if (isset($rewrite_vars[$_qv])) {
                                $redirect['query'] = remove_query_arg($_qv, $redirect['query']);
                            }
                        }
                    }
                }
            }
        } elseif (is_single() && strpos($wp_rewrite->permalink_structure, '%category%') !== false && $cat = get_query_var('category_name')) {
            $category = get_category_by_path($cat);
            $post_terms = wp_get_object_terms($wp_query->get_queried_object_id(), 'category', array('fields' => 'tt_ids'));
            if (!$category || is_wp_error($category) || !is_wp_error($post_terms) && !empty($post_terms) && !in_array($category->term_taxonomy_id, $post_terms)) {
                $redirect_url = get_permalink($wp_query->get_queried_object_id());
            }
        }
        // Post Paging
        if (is_singular() && !is_front_page() && get_query_var('page')) {
            if (!$redirect_url) {
                $redirect_url = get_permalink(get_queried_object_id());
            }
            $redirect_url = trailingslashit($redirect_url) . user_trailingslashit(get_query_var('page'), 'single_paged');
            $redirect['query'] = remove_query_arg('page', $redirect['query']);
        }
        // paging and feeds
        if (get_query_var('paged') || is_feed() || get_query_var('cpage')) {
            while (preg_match("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", $redirect['path']) || preg_match('#/(comments/?)?(feed|rss|rdf|atom|rss2)(/+)?$#', $redirect['path']) || preg_match('#/comment-page-[0-9]+(/+)?$#', $redirect['path'])) {
                // Strip off paging and feed
                $redirect['path'] = preg_replace("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", '/', $redirect['path']);
                // strip off any existing paging
                $redirect['path'] = preg_replace('#/(comments/?)?(feed|rss2?|rdf|atom)(/+|$)#', '/', $redirect['path']);
                // strip off feed endings
                $redirect['path'] = preg_replace('#/comment-page-[0-9]+?(/+)?$#', '/', $redirect['path']);
                // strip off any existing comment paging
            }
            $addl_path = '';
            if (is_feed() && in_array(get_query_var('feed'), $wp_rewrite->feeds)) {
                $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                if (!is_singular() && get_query_var('withcomments')) {
                    $addl_path .= 'comments/';
                }
                if ('rss' == get_default_feed() && 'feed' == get_query_var('feed') || 'rss' == get_query_var('feed')) {
                    $addl_path .= user_trailingslashit('feed/' . ((get_default_feed() == 'rss2') ? '' : 'rss2'), 'feed');
                } else {
                    $addl_path .= user_trailingslashit('feed/' . ((get_default_feed() == get_query_var('feed') || 'feed' == get_query_var('feed')) ? '' : get_query_var('feed')), 'feed');
                }
                $redirect['query'] = remove_query_arg('feed', $redirect['query']);
            } elseif (is_feed() && 'old' == get_query_var('feed')) {
                $old_feed_files = array('wp-atom.php' => 'atom', 'wp-commentsrss2.php' => 'comments_rss2', 'wp-feed.php' => get_default_feed(), 'wp-rdf.php' => 'rdf', 'wp-rss.php' => 'rss2', 'wp-rss2.php' => 'rss2');
                if (isset($old_feed_files[basename($redirect['path'])])) {
                    $redirect_url = get_feed_link($old_feed_files[basename($redirect['path'])]);
                    wp_redirect($redirect_url, 301);
                    die;
                }
            }
            if (get_query_var('paged') > 0) {
                $paged = get_query_var('paged');
                $redirect['query'] = remove_query_arg('paged', $redirect['query']);
                if (!is_feed()) {
                    if ($paged > 1 && !is_single()) {
                        $addl_path = ((!empty($addl_path)) ? trailingslashit($addl_path) : '') . user_trailingslashit("{$wp_rewrite->pagination_base}/{$paged}", 'paged');
                    } elseif (!is_single()) {
                        $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                    }
                } elseif ($paged > 1) {
                    $redirect['query'] = add_query_arg('paged', $paged, $redirect['query']);
                }
            }
            if (get_option('page_comments') && ('newest' == get_option('default_comments_page') && get_query_var('cpage') > 0 || 'newest' != get_option('default_comments_page') && get_query_var('cpage') > 1)) {
                $addl_path = ((!empty($addl_path)) ? trailingslashit($addl_path) : '') . user_trailingslashit('comment-page-' . get_query_var('cpage'), 'commentpaged');
                $redirect['query'] = remove_query_arg('cpage', $redirect['query']);
            }
            $redirect['path'] = user_trailingslashit(preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/?$|', '/', $redirect['path']));
            // strip off trailing /index.php/
            if (!empty($addl_path) && $wp_rewrite->using_index_permalinks() && strpos($redirect['path'], '/' . $wp_rewrite->index . '/') === false) {
                $redirect['path'] = trailingslashit($redirect['path']) . $wp_rewrite->index . '/';
            }
            if (!empty($addl_path)) {
                $redirect['path'] = trailingslashit($redirect['path']) . $addl_path;
            }
            $redirect_url = $redirect['scheme'] . '://' . $redirect['host'] . $redirect['path'];
        }
        if ('wp-register.php' == basename($redirect['path'])) {
            if (is_multisite()) {
                /** This filter is documented in wp-login.php */
                $redirect_url = apply_filters('wp_signup_location', network_site_url('wp-signup.php'));
            } else {
                $redirect_url = site_url('wp-login.php?action=register');
            }
            wp_redirect($redirect_url, 301);
            die;
        }
    }
    // tack on any additional query vars
    $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    if ($redirect_url && !empty($redirect['query'])) {
        parse_str($redirect['query'], $_parsed_query);
        $redirect = @parse_url($redirect_url);
        if (!empty($_parsed_query['name']) && !empty($redirect['query'])) {
            parse_str($redirect['query'], $_parsed_redirect_query);
            if (empty($_parsed_redirect_query['name'])) {
                unset($_parsed_query['name']);
            }
        }
        $_parsed_query = rawurlencode_deep($_parsed_query);
        $redirect_url = add_query_arg($_parsed_query, $redirect_url);
    }
    if ($redirect_url) {
        $redirect = @parse_url($redirect_url);
    }
    // www.example.com vs example.com
    $user_home = @parse_url(home_url());
    if (!empty($user_home['host'])) {
        $redirect['host'] = $user_home['host'];
    }
    if (empty($user_home['path'])) {
        $user_home['path'] = '/';
    }
    // Handle ports
    if (!empty($user_home['port'])) {
        $redirect['port'] = $user_home['port'];
    } else {
        unset($redirect['port']);
    }
    // trailing /index.php
    $redirect['path'] = preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/*?$|', '/', $redirect['path']);
    // Remove trailing spaces from the path
    $redirect['path'] = preg_replace('#(%20| )+$#', '', $redirect['path']);
    if (!empty($redirect['query'])) {
        // Remove trailing spaces from certain terminating query string args
        $redirect['query'] = preg_replace('#((p|page_id|cat|tag)=[^&]*?)(%20| )+$#', '$1', $redirect['query']);
        // Clean up empty query strings
        $redirect['query'] = trim(preg_replace('#(^|&)(p|page_id|cat|tag)=?(&|$)#', '&', $redirect['query']), '&');
        // Redirect obsolete feeds
        $redirect['query'] = preg_replace('#(^|&)feed=rss(&|$)#', '$1feed=rss2$2', $redirect['query']);
        // Remove redundant leading ampersands
        $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    }
    // strip /index.php/ when we're not using PATHINFO permalinks
    if (!$wp_rewrite->using_index_permalinks()) {
        $redirect['path'] = str_replace('/' . $wp_rewrite->index . '/', '/', $redirect['path']);
    }
    // trailing slashes
    if (is_object($wp_rewrite) && $wp_rewrite->using_permalinks() && !is_404() && (!is_front_page() || is_front_page() && get_query_var('paged') > 1)) {
        $user_ts_type = '';
        if (get_query_var('paged') > 0) {
            $user_ts_type = 'paged';
        } else {
            foreach (array('single', 'category', 'page', 'day', 'month', 'year', 'home') as $type) {
                $func = 'is_' . $type;
                if (call_user_func($func)) {
                    $user_ts_type = $type;
                    break;
                }
            }
        }
        $redirect['path'] = user_trailingslashit($redirect['path'], $user_ts_type);
    } elseif (is_front_page()) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Strip multiple slashes out of the URL
    if (strpos($redirect['path'], '//') > -1) {
        $redirect['path'] = preg_replace('|/+|', '/', $redirect['path']);
    }
    // Always trailing slash the Front Page URL
    if (trailingslashit($redirect['path']) == trailingslashit($user_home['path'])) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Ignore differences in host capitalization, as this can lead to infinite redirects
    // Only redirect no-www <=> yes-www
    if (strtolower($original['host']) == strtolower($redirect['host']) || strtolower($original['host']) != 'www.' . strtolower($redirect['host']) && 'www.' . strtolower($original['host']) != strtolower($redirect['host'])) {
        $redirect['host'] = $original['host'];
    }
    $compare_original = array($original['host'], $original['path']);
    if (!empty($original['port'])) {
        $compare_original[] = $original['port'];
    }
    if (!empty($original['query'])) {
        $compare_original[] = $original['query'];
    }
    $compare_redirect = array($redirect['host'], $redirect['path']);
    if (!empty($redirect['port'])) {
        $compare_redirect[] = $redirect['port'];
    }
    if (!empty($redirect['query'])) {
        $compare_redirect[] = $redirect['query'];
    }
    if ($compare_original !== $compare_redirect) {
        $redirect_url = $redirect['scheme'] . '://' . $redirect['host'];
        if (!empty($redirect['port'])) {
            $redirect_url .= ':' . $redirect['port'];
        }
        $redirect_url .= $redirect['path'];
        if (!empty($redirect['query'])) {
            $redirect_url .= '?' . $redirect['query'];
        }
    }
    if (!$redirect_url || $redirect_url == $requested_url) {
        return false;
    }
    // Hex encoded octets are case-insensitive.
    if (false !== strpos($requested_url, '%')) {
        if (!function_exists('lowercase_octets')) {
            function lowercase_octets($matches)
            {
                return strtolower($matches[0]);
            }
        }
        $requested_url = preg_replace_callback('|%[a-fA-F0-9][a-fA-F0-9]|', 'lowercase_octets', $requested_url);
    }
    /**
     * Filter the canonical redirect URL.
     *
     * Returning false to this filter will cancel the redirect.
     *
     * @since 2.3.0
     *
     * @param string $redirect_url  The redirect URL.
     * @param string $requested_url The requested URL.
     */
    $redirect_url = apply_filters('redirect_canonical', $redirect_url, $requested_url);
    if (!$redirect_url || $redirect_url == $requested_url) {
        // yes, again -- in case the filter aborted the request
        return false;
    }
    if ($do_redirect) {
        // protect against chained redirects
        if (!redirect_canonical($redirect_url, false)) {
            wp_redirect($redirect_url, 301);
            exit;
        } else {
            // Debug
            // die("1: $redirect_url<br />2: " . redirect_canonical( $redirect_url, false ) );
            return false;
        }
    } else {
        return $redirect_url;
    }
}

WordPress Version: 4.0

/**
 * Canonical API to handle WordPress Redirecting
 *
 * Based on "Permalink Redirect" from Scott Yang and "Enforce www. Preference"
 * by Mark Jaquith
 *
 * @package WordPress
 * @since 2.3.0
 */
/**
 * Redirects incoming links to the proper URL based on the site url.
 *
 * Search engines consider www.somedomain.com and somedomain.com to be two
 * different URLs when they both go to the same location. This SEO enhancement
 * prevents penalty for duplicate content by redirecting all incoming links to
 * one or the other.
 *
 * Prevents redirection for feeds, trackbacks, searches, comment popup, and
 * admin URLs. Does not redirect on non-pretty-permalink-supporting IIS 7+,
 * page/post previews, WP admin, Trackbacks, robots.txt, searches, or on POST
 * requests.
 *
 * Will also attempt to find the correct link when a user enters a URL that does
 * not exist based on exact WordPress query. Will instead try to parse the URL
 * or query in an attempt to figure the correct page to go to.
 *
 * @since 2.3.0
 * @uses $wp_rewrite
 * @uses $is_IIS
 *
 * @param string $requested_url Optional. The URL that was requested, used to
 *		figure if redirect is needed.
 * @param bool $do_redirect Optional. Redirect to the new URL.
 * @return null|false|string Null, if redirect not needed. False, if redirect
 *		not needed or the string of the URL
 */
function redirect_canonical($requested_url = null, $do_redirect = true)
{
    global $wp_rewrite, $is_IIS, $wp_query, $wpdb;
    if (isset($_SERVER['REQUEST_METHOD']) && !in_array(strtoupper($_SERVER['REQUEST_METHOD']), array('GET', 'HEAD'))) {
        return;
    }
    // If we're not in wp-admin and the post has been published and preview nonce
    // is non-existent or invalid then no need for preview in query
    if (is_preview() && get_query_var('p') && 'publish' == get_post_status(get_query_var('p'))) {
        if (!isset($_GET['preview_id']) || !isset($_GET['preview_nonce']) || !wp_verify_nonce($_GET['preview_nonce'], 'post_preview_' . (int) $_GET['preview_id'])) {
            $wp_query->is_preview = false;
        }
    }
    if (is_trackback() || is_search() || is_comments_popup() || is_admin() || is_preview() || is_robots() || $is_IIS && !iis7_supports_permalinks()) {
        return;
    }
    if (!$requested_url) {
        // build the URL in the address bar
        $requested_url = is_ssl() ? 'https://' : 'http://';
        $requested_url .= $_SERVER['HTTP_HOST'];
        $requested_url .= $_SERVER['REQUEST_URI'];
    }
    $original = @parse_url($requested_url);
    if (false === $original) {
        return;
    }
    // Some PHP setups turn requests for / into /index.php in REQUEST_URI
    // See: http://trac.wordpress.org/ticket/5017
    // See: http://trac.wordpress.org/ticket/7173
    // Disabled, for now:
    // $original['path'] = preg_replace('|/index\.php$|', '/', $original['path']);
    $redirect = $original;
    $redirect_url = false;
    // Notice fixing
    if (!isset($redirect['path'])) {
        $redirect['path'] = '';
    }
    if (!isset($redirect['query'])) {
        $redirect['query'] = '';
    }
    // It's not a preview, so remove it from URL
    if (get_query_var('preview')) {
        $redirect['query'] = remove_query_arg('preview', $redirect['query']);
    }
    if (is_feed() && $id = get_query_var('p')) {
        if ($redirect_url = get_post_comments_feed_link($id, get_query_var('feed'))) {
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type', 'feed'), $redirect_url);
            $redirect['path'] = parse_url($redirect_url, PHP_URL_PATH);
        }
    }
    if (is_singular() && 1 > $wp_query->post_count && $id = get_query_var('p')) {
        $vars = $wpdb->get_results($wpdb->prepare("SELECT post_type, post_parent FROM {$wpdb->posts} WHERE ID = %d", $id));
        if (isset($vars[0]) && $vars = $vars[0]) {
            if ('revision' == $vars->post_type && $vars->post_parent > 0) {
                $id = $vars->post_parent;
            }
            if ($redirect_url = get_permalink($id)) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    }
    // These tests give us a WP-generated permalink
    if (is_404()) {
        // Redirect ?page_id, ?p=, ?attachment_id= to their respective url's
        $id = max(get_query_var('p'), get_query_var('page_id'), get_query_var('attachment_id'));
        if ($id && $redirect_post = get_post($id)) {
            $post_type_obj = get_post_type_object($redirect_post->post_type);
            if ($post_type_obj->public) {
                $redirect_url = get_permalink($redirect_post);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
        if (get_query_var('day') && get_query_var('monthnum') && get_query_var('year')) {
            $year = get_query_var('year');
            $month = get_query_var('monthnum');
            $day = get_query_var('day');
            $date = sprintf('%04d-%02d-%02d', $year, $month, $day);
            if (!wp_checkdate($month, $day, $year, $date)) {
                $redirect_url = get_month_link($year, $month);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum', 'day'), $redirect_url);
            }
        } elseif (get_query_var('monthnum') && get_query_var('year') && 12 < get_query_var('monthnum')) {
            $redirect_url = get_year_link(get_query_var('year'));
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum'), $redirect_url);
        }
        if (!$redirect_url) {
            if ($redirect_url = redirect_guess_404_permalink()) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('page', 'feed', 'p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    } elseif (is_object($wp_rewrite) && $wp_rewrite->using_permalinks()) {
        // rewriting of old ?p=X, ?m=2004, ?m=200401, ?m=20040101
        if (is_attachment() && !empty($_GET['attachment_id']) && !$redirect_url) {
            if ($redirect_url = get_attachment_link(get_query_var('attachment_id'))) {
                $redirect['query'] = remove_query_arg('attachment_id', $redirect['query']);
            }
        } elseif (is_single() && !empty($_GET['p']) && !$redirect_url) {
            if ($redirect_url = get_permalink(get_query_var('p'))) {
                $redirect['query'] = remove_query_arg(array('p', 'post_type'), $redirect['query']);
            }
        } elseif (is_single() && !empty($_GET['name']) && !$redirect_url) {
            if ($redirect_url = get_permalink($wp_query->get_queried_object_id())) {
                $redirect['query'] = remove_query_arg('name', $redirect['query']);
            }
        } elseif (is_page() && !empty($_GET['page_id']) && !$redirect_url) {
            if ($redirect_url = get_permalink(get_query_var('page_id'))) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (is_page() && !is_feed() && isset($wp_query->queried_object) && 'page' == get_option('show_on_front') && $wp_query->queried_object->ID == get_option('page_on_front') && !$redirect_url) {
            $redirect_url = home_url('/');
        } elseif (is_home() && !empty($_GET['page_id']) && 'page' == get_option('show_on_front') && get_query_var('page_id') == get_option('page_for_posts') && !$redirect_url) {
            if ($redirect_url = get_permalink(get_option('page_for_posts'))) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (!empty($_GET['m']) && (is_year() || is_month() || is_day())) {
            $m = get_query_var('m');
            switch (strlen($m)) {
                case 4:
                    // Yearly
                    $redirect_url = get_year_link($m);
                    break;
                case 6:
                    // Monthly
                    $redirect_url = get_month_link(substr($m, 0, 4), substr($m, 4, 2));
                    break;
                case 8:
                    // Daily
                    $redirect_url = get_day_link(substr($m, 0, 4), substr($m, 4, 2), substr($m, 6, 2));
                    break;
            }
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('m', $redirect['query']);
            }
            // now moving on to non ?m=X year/month/day links
        } elseif (is_day() && get_query_var('year') && get_query_var('monthnum') && !empty($_GET['day'])) {
            if ($redirect_url = get_day_link(get_query_var('year'), get_query_var('monthnum'), get_query_var('day'))) {
                $redirect['query'] = remove_query_arg(array('year', 'monthnum', 'day'), $redirect['query']);
            }
        } elseif (is_month() && get_query_var('year') && !empty($_GET['monthnum'])) {
            if ($redirect_url = get_month_link(get_query_var('year'), get_query_var('monthnum'))) {
                $redirect['query'] = remove_query_arg(array('year', 'monthnum'), $redirect['query']);
            }
        } elseif (is_year() && !empty($_GET['year'])) {
            if ($redirect_url = get_year_link(get_query_var('year'))) {
                $redirect['query'] = remove_query_arg('year', $redirect['query']);
            }
        } elseif (is_author() && !empty($_GET['author']) && preg_match('|^[0-9]+$|', $_GET['author'])) {
            $author = get_userdata(get_query_var('author'));
            if (false !== $author && $wpdb->get_var($wpdb->prepare("SELECT ID FROM {$wpdb->posts} WHERE {$wpdb->posts}.post_author = %d AND {$wpdb->posts}.post_status = 'publish' LIMIT 1", $author->ID))) {
                if ($redirect_url = get_author_posts_url($author->ID, $author->user_nicename)) {
                    $redirect['query'] = remove_query_arg('author', $redirect['query']);
                }
            }
        } elseif (is_category() || is_tag() || is_tax()) {
            // Terms (Tags/categories)
            $term_count = 0;
            foreach ($wp_query->tax_query->queries as $tax_query) {
                $term_count += count($tax_query['terms']);
            }
            $obj = $wp_query->get_queried_object();
            if ($term_count <= 1 && !empty($obj->term_id) && ($tax_url = get_term_link((int) $obj->term_id, $obj->taxonomy)) && !is_wp_error($tax_url)) {
                if (!empty($redirect['query'])) {
                    // Strip taxonomy query vars off the url.
                    $qv_remove = array('term', 'taxonomy');
                    if (is_category()) {
                        $qv_remove[] = 'category_name';
                        $qv_remove[] = 'cat';
                    } elseif (is_tag()) {
                        $qv_remove[] = 'tag';
                        $qv_remove[] = 'tag_id';
                    } else {
                        // Custom taxonomies will have a custom query var, remove those too:
                        $tax_obj = get_taxonomy($obj->taxonomy);
                        if (false !== $tax_obj->query_var) {
                            $qv_remove[] = $tax_obj->query_var;
                        }
                    }
                    $rewrite_vars = array_diff(array_keys($wp_query->query), array_keys($_GET));
                    if (!array_diff($rewrite_vars, array_keys($_GET))) {
                        // Check to see if all the Query vars are coming from the rewrite, none are set via $_GET
                        $redirect['query'] = remove_query_arg($qv_remove, $redirect['query']);
                        //Remove all of the per-tax qv's
                        // Create the destination url for this taxonomy
                        $tax_url = parse_url($tax_url);
                        if (!empty($tax_url['query'])) {
                            // Taxonomy accessible via ?taxonomy=..&term=.. or any custom qv..
                            parse_str($tax_url['query'], $query_vars);
                            $redirect['query'] = add_query_arg($query_vars, $redirect['query']);
                        } else {
                            // Taxonomy is accessible via a "pretty-URL"
                            $redirect['path'] = $tax_url['path'];
                        }
                    } else {
                        // Some query vars are set via $_GET. Unset those from $_GET that exist via the rewrite
                        foreach ($qv_remove as $_qv) {
                            if (isset($rewrite_vars[$_qv])) {
                                $redirect['query'] = remove_query_arg($_qv, $redirect['query']);
                            }
                        }
                    }
                }
            }
        } elseif (is_single() && strpos($wp_rewrite->permalink_structure, '%category%') !== false && $cat = get_query_var('category_name')) {
            $category = get_category_by_path($cat);
            $post_terms = wp_get_object_terms($wp_query->get_queried_object_id(), 'category', array('fields' => 'tt_ids'));
            if (!$category || is_wp_error($category) || !is_wp_error($post_terms) && !empty($post_terms) && !in_array($category->term_taxonomy_id, $post_terms)) {
                $redirect_url = get_permalink($wp_query->get_queried_object_id());
            }
        }
        // Post Paging
        if (is_singular() && !is_front_page() && get_query_var('page')) {
            if (!$redirect_url) {
                $redirect_url = get_permalink(get_queried_object_id());
            }
            $redirect_url = trailingslashit($redirect_url) . user_trailingslashit(get_query_var('page'), 'single_paged');
            $redirect['query'] = remove_query_arg('page', $redirect['query']);
        }
        // paging and feeds
        if (get_query_var('paged') || is_feed() || get_query_var('cpage')) {
            while (preg_match("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", $redirect['path']) || preg_match('#/(comments/?)?(feed|rss|rdf|atom|rss2)(/+)?$#', $redirect['path']) || preg_match('#/comment-page-[0-9]+(/+)?$#', $redirect['path'])) {
                // Strip off paging and feed
                $redirect['path'] = preg_replace("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", '/', $redirect['path']);
                // strip off any existing paging
                $redirect['path'] = preg_replace('#/(comments/?)?(feed|rss2?|rdf|atom)(/+|$)#', '/', $redirect['path']);
                // strip off feed endings
                $redirect['path'] = preg_replace('#/comment-page-[0-9]+?(/+)?$#', '/', $redirect['path']);
                // strip off any existing comment paging
            }
            $addl_path = '';
            if (is_feed() && in_array(get_query_var('feed'), $wp_rewrite->feeds)) {
                $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                if (!is_singular() && get_query_var('withcomments')) {
                    $addl_path .= 'comments/';
                }
                if ('rss' == get_default_feed() && 'feed' == get_query_var('feed') || 'rss' == get_query_var('feed')) {
                    $addl_path .= user_trailingslashit('feed/' . ((get_default_feed() == 'rss2') ? '' : 'rss2'), 'feed');
                } else {
                    $addl_path .= user_trailingslashit('feed/' . ((get_default_feed() == get_query_var('feed') || 'feed' == get_query_var('feed')) ? '' : get_query_var('feed')), 'feed');
                }
                $redirect['query'] = remove_query_arg('feed', $redirect['query']);
            } elseif (is_feed() && 'old' == get_query_var('feed')) {
                $old_feed_files = array('wp-atom.php' => 'atom', 'wp-commentsrss2.php' => 'comments_rss2', 'wp-feed.php' => get_default_feed(), 'wp-rdf.php' => 'rdf', 'wp-rss.php' => 'rss2', 'wp-rss2.php' => 'rss2');
                if (isset($old_feed_files[basename($redirect['path'])])) {
                    $redirect_url = get_feed_link($old_feed_files[basename($redirect['path'])]);
                    wp_redirect($redirect_url, 301);
                    die;
                }
            }
            if (get_query_var('paged') > 0) {
                $paged = get_query_var('paged');
                $redirect['query'] = remove_query_arg('paged', $redirect['query']);
                if (!is_feed()) {
                    if ($paged > 1 && !is_single()) {
                        $addl_path = ((!empty($addl_path)) ? trailingslashit($addl_path) : '') . user_trailingslashit("{$wp_rewrite->pagination_base}/{$paged}", 'paged');
                    } elseif (!is_single()) {
                        $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                    }
                } elseif ($paged > 1) {
                    $redirect['query'] = add_query_arg('paged', $paged, $redirect['query']);
                }
            }
            if (get_option('page_comments') && ('newest' == get_option('default_comments_page') && get_query_var('cpage') > 0 || 'newest' != get_option('default_comments_page') && get_query_var('cpage') > 1)) {
                $addl_path = ((!empty($addl_path)) ? trailingslashit($addl_path) : '') . user_trailingslashit('comment-page-' . get_query_var('cpage'), 'commentpaged');
                $redirect['query'] = remove_query_arg('cpage', $redirect['query']);
            }
            $redirect['path'] = user_trailingslashit(preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/?$|', '/', $redirect['path']));
            // strip off trailing /index.php/
            if (!empty($addl_path) && $wp_rewrite->using_index_permalinks() && strpos($redirect['path'], '/' . $wp_rewrite->index . '/') === false) {
                $redirect['path'] = trailingslashit($redirect['path']) . $wp_rewrite->index . '/';
            }
            if (!empty($addl_path)) {
                $redirect['path'] = trailingslashit($redirect['path']) . $addl_path;
            }
            $redirect_url = $redirect['scheme'] . '://' . $redirect['host'] . $redirect['path'];
        }
        if ('wp-register.php' == basename($redirect['path'])) {
            if (is_multisite()) {
                /** This filter is documented in wp-login.php */
                $redirect_url = apply_filters('wp_signup_location', network_site_url('wp-signup.php'));
            } else {
                $redirect_url = site_url('wp-login.php?action=register');
            }
            wp_redirect($redirect_url, 301);
            die;
        }
    }
    // tack on any additional query vars
    $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    if ($redirect_url && !empty($redirect['query'])) {
        parse_str($redirect['query'], $_parsed_query);
        $redirect = @parse_url($redirect_url);
        if (!empty($_parsed_query['name']) && !empty($redirect['query'])) {
            parse_str($redirect['query'], $_parsed_redirect_query);
            if (empty($_parsed_redirect_query['name'])) {
                unset($_parsed_query['name']);
            }
        }
        $_parsed_query = rawurlencode_deep($_parsed_query);
        $redirect_url = add_query_arg($_parsed_query, $redirect_url);
    }
    if ($redirect_url) {
        $redirect = @parse_url($redirect_url);
    }
    // www.example.com vs example.com
    $user_home = @parse_url(home_url());
    if (!empty($user_home['host'])) {
        $redirect['host'] = $user_home['host'];
    }
    if (empty($user_home['path'])) {
        $user_home['path'] = '/';
    }
    // Handle ports
    if (!empty($user_home['port'])) {
        $redirect['port'] = $user_home['port'];
    } else {
        unset($redirect['port']);
    }
    if (!empty($user_home['scheme']) && $user_home['scheme'] === 'https') {
        $redirect['scheme'] = 'https';
    }
    // trailing /index.php
    $redirect['path'] = preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/*?$|', '/', $redirect['path']);
    // Remove trailing spaces from the path
    $redirect['path'] = preg_replace('#(%20| )+$#', '', $redirect['path']);
    if (!empty($redirect['query'])) {
        // Remove trailing spaces from certain terminating query string args
        $redirect['query'] = preg_replace('#((p|page_id|cat|tag)=[^&]*?)(%20| )+$#', '$1', $redirect['query']);
        // Clean up empty query strings
        $redirect['query'] = trim(preg_replace('#(^|&)(p|page_id|cat|tag)=?(&|$)#', '&', $redirect['query']), '&');
        // Redirect obsolete feeds
        $redirect['query'] = preg_replace('#(^|&)feed=rss(&|$)#', '$1feed=rss2$2', $redirect['query']);
        // Remove redundant leading ampersands
        $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    }
    // strip /index.php/ when we're not using PATHINFO permalinks
    if (!$wp_rewrite->using_index_permalinks()) {
        $redirect['path'] = str_replace('/' . $wp_rewrite->index . '/', '/', $redirect['path']);
    }
    // trailing slashes
    if (is_object($wp_rewrite) && $wp_rewrite->using_permalinks() && !is_404() && (!is_front_page() || is_front_page() && get_query_var('paged') > 1)) {
        $user_ts_type = '';
        if (get_query_var('paged') > 0) {
            $user_ts_type = 'paged';
        } else {
            foreach (array('single', 'category', 'page', 'day', 'month', 'year', 'home') as $type) {
                $func = 'is_' . $type;
                if (call_user_func($func)) {
                    $user_ts_type = $type;
                    break;
                }
            }
        }
        $redirect['path'] = user_trailingslashit($redirect['path'], $user_ts_type);
    } elseif (is_front_page()) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Strip multiple slashes out of the URL
    if (strpos($redirect['path'], '//') > -1) {
        $redirect['path'] = preg_replace('|/+|', '/', $redirect['path']);
    }
    // Always trailing slash the Front Page URL
    if (trailingslashit($redirect['path']) == trailingslashit($user_home['path'])) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Ignore differences in host capitalization, as this can lead to infinite redirects
    // Only redirect no-www <=> yes-www
    if (strtolower($original['host']) == strtolower($redirect['host']) || strtolower($original['host']) != 'www.' . strtolower($redirect['host']) && 'www.' . strtolower($original['host']) != strtolower($redirect['host'])) {
        $redirect['host'] = $original['host'];
    }
    $compare_original = array($original['scheme'], $original['host'], $original['path']);
    if (!empty($original['port'])) {
        $compare_original[] = $original['port'];
    }
    if (!empty($original['query'])) {
        $compare_original[] = $original['query'];
    }
    $compare_redirect = array($redirect['scheme'], $redirect['host'], $redirect['path']);
    if (!empty($redirect['port'])) {
        $compare_redirect[] = $redirect['port'];
    }
    if (!empty($redirect['query'])) {
        $compare_redirect[] = $redirect['query'];
    }
    if ($compare_original !== $compare_redirect) {
        $redirect_url = $redirect['scheme'] . '://' . $redirect['host'];
        if (!empty($redirect['port'])) {
            $redirect_url .= ':' . $redirect['port'];
        }
        $redirect_url .= $redirect['path'];
        if (!empty($redirect['query'])) {
            $redirect_url .= '?' . $redirect['query'];
        }
    }
    if (!$redirect_url || $redirect_url == $requested_url) {
        return false;
    }
    // Hex encoded octets are case-insensitive.
    if (false !== strpos($requested_url, '%')) {
        if (!function_exists('lowercase_octets')) {
            function lowercase_octets($matches)
            {
                return strtolower($matches[0]);
            }
        }
        $requested_url = preg_replace_callback('|%[a-fA-F0-9][a-fA-F0-9]|', 'lowercase_octets', $requested_url);
    }
    /**
     * Filter the canonical redirect URL.
     *
     * Returning false to this filter will cancel the redirect.
     *
     * @since 2.3.0
     *
     * @param string $redirect_url  The redirect URL.
     * @param string $requested_url The requested URL.
     */
    $redirect_url = apply_filters('redirect_canonical', $redirect_url, $requested_url);
    if (!$redirect_url || $redirect_url == $requested_url) {
        // yes, again -- in case the filter aborted the request
        return false;
    }
    if ($do_redirect) {
        // protect against chained redirects
        if (!redirect_canonical($redirect_url, false)) {
            wp_redirect($redirect_url, 301);
            exit;
        } else {
            // Debug
            // die("1: $redirect_url<br />2: " . redirect_canonical( $redirect_url, false ) );
            return false;
        }
    } else {
        return $redirect_url;
    }
}

WordPress Version: 3.7

/**
 * Canonical API to handle WordPress Redirecting
 *
 * Based on "Permalink Redirect" from Scott Yang and "Enforce www. Preference"
 * by Mark Jaquith
 *
 * @package WordPress
 * @since 2.3.0
 */
/**
 * Redirects incoming links to the proper URL based on the site url.
 *
 * Search engines consider www.somedomain.com and somedomain.com to be two
 * different URLs when they both go to the same location. This SEO enhancement
 * prevents penalty for duplicate content by redirecting all incoming links to
 * one or the other.
 *
 * Prevents redirection for feeds, trackbacks, searches, comment popup, and
 * admin URLs. Does not redirect on non-pretty-permalink-supporting IIS 7+,
 * page/post previews, WP admin, Trackbacks, robots.txt, searches, or on POST
 * requests.
 *
 * Will also attempt to find the correct link when a user enters a URL that does
 * not exist based on exact WordPress query. Will instead try to parse the URL
 * or query in an attempt to figure the correct page to go to.
 *
 * @since 2.3.0
 * @uses $wp_rewrite
 * @uses $is_IIS
 *
 * @param string $requested_url Optional. The URL that was requested, used to
 *		figure if redirect is needed.
 * @param bool $do_redirect Optional. Redirect to the new URL.
 * @return null|false|string Null, if redirect not needed. False, if redirect
 *		not needed or the string of the URL
 */
function redirect_canonical($requested_url = null, $do_redirect = true)
{
    global $wp_rewrite, $is_IIS, $wp_query, $wpdb;
    if (is_trackback() || is_search() || is_comments_popup() || is_admin() || !empty($_POST) || is_preview() || is_robots() || $is_IIS && !iis7_supports_permalinks()) {
        return;
    }
    if (!$requested_url) {
        // build the URL in the address bar
        $requested_url = is_ssl() ? 'https://' : 'http://';
        $requested_url .= $_SERVER['HTTP_HOST'];
        $requested_url .= $_SERVER['REQUEST_URI'];
    }
    $original = @parse_url($requested_url);
    if (false === $original) {
        return;
    }
    // Some PHP setups turn requests for / into /index.php in REQUEST_URI
    // See: http://trac.wordpress.org/ticket/5017
    // See: http://trac.wordpress.org/ticket/7173
    // Disabled, for now:
    // $original['path'] = preg_replace('|/index\.php$|', '/', $original['path']);
    $redirect = $original;
    $redirect_url = false;
    // Notice fixing
    if (!isset($redirect['path'])) {
        $redirect['path'] = '';
    }
    if (!isset($redirect['query'])) {
        $redirect['query'] = '';
    }
    if (is_feed() && $id = get_query_var('p')) {
        if ($redirect_url = get_post_comments_feed_link($id, get_query_var('feed'))) {
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type', 'feed'), $redirect_url);
            $redirect['path'] = parse_url($redirect_url, PHP_URL_PATH);
        }
    }
    if (is_singular() && 1 > $wp_query->post_count && $id = get_query_var('p')) {
        $vars = $wpdb->get_results($wpdb->prepare("SELECT post_type, post_parent FROM {$wpdb->posts} WHERE ID = %d", $id));
        if (isset($vars[0]) && $vars = $vars[0]) {
            if ('revision' == $vars->post_type && $vars->post_parent > 0) {
                $id = $vars->post_parent;
            }
            if ($redirect_url = get_permalink($id)) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    }
    // These tests give us a WP-generated permalink
    if (is_404()) {
        // Redirect ?page_id, ?p=, ?attachment_id= to their respective url's
        $id = max(get_query_var('p'), get_query_var('page_id'), get_query_var('attachment_id'));
        if ($id && $redirect_post = get_post($id)) {
            $post_type_obj = get_post_type_object($redirect_post->post_type);
            if ($post_type_obj->public) {
                $redirect_url = get_permalink($redirect_post);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
        if (get_query_var('day') && get_query_var('monthnum') && get_query_var('year')) {
            $year = get_query_var('year');
            $month = get_query_var('monthnum');
            $day = get_query_var('day');
            $date = sprintf('%04d-%02d-%02d', $year, $month, $day);
            if (!wp_checkdate($month, $day, $year, $date)) {
                $redirect_url = get_month_link($year, $month);
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum', 'day'), $redirect_url);
            }
        } elseif (get_query_var('monthnum') && get_query_var('year') && 12 < get_query_var('monthnum')) {
            $redirect_url = get_year_link(get_query_var('year'));
            $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('year', 'monthnum'), $redirect_url);
        }
        if (!$redirect_url) {
            if ($redirect_url = redirect_guess_404_permalink()) {
                $redirect['query'] = _remove_qs_args_if_not_in_url($redirect['query'], array('page', 'feed', 'p', 'page_id', 'attachment_id', 'pagename', 'name', 'post_type'), $redirect_url);
            }
        }
    } elseif (is_object($wp_rewrite) && $wp_rewrite->using_permalinks()) {
        // rewriting of old ?p=X, ?m=2004, ?m=200401, ?m=20040101
        if (is_attachment() && !empty($_GET['attachment_id']) && !$redirect_url) {
            if ($redirect_url = get_attachment_link(get_query_var('attachment_id'))) {
                $redirect['query'] = remove_query_arg('attachment_id', $redirect['query']);
            }
        } elseif (is_single() && !empty($_GET['p']) && !$redirect_url) {
            if ($redirect_url = get_permalink(get_query_var('p'))) {
                $redirect['query'] = remove_query_arg(array('p', 'post_type'), $redirect['query']);
            }
        } elseif (is_single() && !empty($_GET['name']) && !$redirect_url) {
            if ($redirect_url = get_permalink($wp_query->get_queried_object_id())) {
                $redirect['query'] = remove_query_arg('name', $redirect['query']);
            }
        } elseif (is_page() && !empty($_GET['page_id']) && !$redirect_url) {
            if ($redirect_url = get_permalink(get_query_var('page_id'))) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (is_page() && !is_feed() && isset($wp_query->queried_object) && 'page' == get_option('show_on_front') && $wp_query->queried_object->ID == get_option('page_on_front') && !$redirect_url) {
            $redirect_url = home_url('/');
        } elseif (is_home() && !empty($_GET['page_id']) && 'page' == get_option('show_on_front') && get_query_var('page_id') == get_option('page_for_posts') && !$redirect_url) {
            if ($redirect_url = get_permalink(get_option('page_for_posts'))) {
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
            }
        } elseif (!empty($_GET['m']) && (is_year() || is_month() || is_day())) {
            $m = get_query_var('m');
            switch (strlen($m)) {
                case 4:
                    // Yearly
                    $redirect_url = get_year_link($m);
                    break;
                case 6:
                    // Monthly
                    $redirect_url = get_month_link(substr($m, 0, 4), substr($m, 4, 2));
                    break;
                case 8:
                    // Daily
                    $redirect_url = get_day_link(substr($m, 0, 4), substr($m, 4, 2), substr($m, 6, 2));
                    break;
            }
            if ($redirect_url) {
                $redirect['query'] = remove_query_arg('m', $redirect['query']);
            }
            // now moving on to non ?m=X year/month/day links
        } elseif (is_day() && get_query_var('year') && get_query_var('monthnum') && !empty($_GET['day'])) {
            if ($redirect_url = get_day_link(get_query_var('year'), get_query_var('monthnum'), get_query_var('day'))) {
                $redirect['query'] = remove_query_arg(array('year', 'monthnum', 'day'), $redirect['query']);
            }
        } elseif (is_month() && get_query_var('year') && !empty($_GET['monthnum'])) {
            if ($redirect_url = get_month_link(get_query_var('year'), get_query_var('monthnum'))) {
                $redirect['query'] = remove_query_arg(array('year', 'monthnum'), $redirect['query']);
            }
        } elseif (is_year() && !empty($_GET['year'])) {
            if ($redirect_url = get_year_link(get_query_var('year'))) {
                $redirect['query'] = remove_query_arg('year', $redirect['query']);
            }
        } elseif (is_author() && !empty($_GET['author']) && preg_match('|^[0-9]+$|', $_GET['author'])) {
            $author = get_userdata(get_query_var('author'));
            if (false !== $author && $wpdb->get_var($wpdb->prepare("SELECT ID FROM {$wpdb->posts} WHERE {$wpdb->posts}.post_author = %d AND {$wpdb->posts}.post_status = 'publish' LIMIT 1", $author->ID))) {
                if ($redirect_url = get_author_posts_url($author->ID, $author->user_nicename)) {
                    $redirect['query'] = remove_query_arg('author', $redirect['query']);
                }
            }
        } elseif (is_category() || is_tag() || is_tax()) {
            // Terms (Tags/categories)
            $term_count = 0;
            foreach ($wp_query->tax_query->queries as $tax_query) {
                $term_count += count($tax_query['terms']);
            }
            $obj = $wp_query->get_queried_object();
            if ($term_count <= 1 && !empty($obj->term_id) && ($tax_url = get_term_link((int) $obj->term_id, $obj->taxonomy)) && !is_wp_error($tax_url)) {
                if (!empty($redirect['query'])) {
                    // Strip taxonomy query vars off the url.
                    $qv_remove = array('term', 'taxonomy');
                    if (is_category()) {
                        $qv_remove[] = 'category_name';
                        $qv_remove[] = 'cat';
                    } elseif (is_tag()) {
                        $qv_remove[] = 'tag';
                        $qv_remove[] = 'tag_id';
                    } else {
                        // Custom taxonomies will have a custom query var, remove those too:
                        $tax_obj = get_taxonomy($obj->taxonomy);
                        if (false !== $tax_obj->query_var) {
                            $qv_remove[] = $tax_obj->query_var;
                        }
                    }
                    $rewrite_vars = array_diff(array_keys($wp_query->query), array_keys($_GET));
                    if (!array_diff($rewrite_vars, array_keys($_GET))) {
                        // Check to see if all the Query vars are coming from the rewrite, none are set via $_GET
                        $redirect['query'] = remove_query_arg($qv_remove, $redirect['query']);
                        //Remove all of the per-tax qv's
                        // Create the destination url for this taxonomy
                        $tax_url = parse_url($tax_url);
                        if (!empty($tax_url['query'])) {
                            // Taxonomy accessible via ?taxonomy=..&term=.. or any custom qv..
                            parse_str($tax_url['query'], $query_vars);
                            $redirect['query'] = add_query_arg($query_vars, $redirect['query']);
                        } else {
                            // Taxonomy is accessible via a "pretty-URL"
                            $redirect['path'] = $tax_url['path'];
                        }
                    } else {
                        // Some query vars are set via $_GET. Unset those from $_GET that exist via the rewrite
                        foreach ($qv_remove as $_qv) {
                            if (isset($rewrite_vars[$_qv])) {
                                $redirect['query'] = remove_query_arg($_qv, $redirect['query']);
                            }
                        }
                    }
                }
            }
        } elseif (is_single() && strpos($wp_rewrite->permalink_structure, '%category%') !== false && $cat = get_query_var('category_name')) {
            $category = get_category_by_path($cat);
            $post_terms = wp_get_object_terms($wp_query->get_queried_object_id(), 'category', array('fields' => 'tt_ids'));
            if (!$category || is_wp_error($category) || !is_wp_error($post_terms) && !empty($post_terms) && !in_array($category->term_taxonomy_id, $post_terms)) {
                $redirect_url = get_permalink($wp_query->get_queried_object_id());
            }
        }
        // Post Paging
        if (is_singular() && !is_front_page() && get_query_var('page')) {
            if (!$redirect_url) {
                $redirect_url = get_permalink(get_queried_object_id());
            }
            $redirect_url = trailingslashit($redirect_url) . user_trailingslashit(get_query_var('page'), 'single_paged');
            $redirect['query'] = remove_query_arg('page', $redirect['query']);
        }
        // paging and feeds
        if (get_query_var('paged') || is_feed() || get_query_var('cpage')) {
            while (preg_match("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", $redirect['path']) || preg_match('#/(comments/?)?(feed|rss|rdf|atom|rss2)(/+)?$#', $redirect['path']) || preg_match('#/comment-page-[0-9]+(/+)?$#', $redirect['path'])) {
                // Strip off paging and feed
                $redirect['path'] = preg_replace("#/{$wp_rewrite->pagination_base}/?[0-9]+?(/+)?\$#", '/', $redirect['path']);
                // strip off any existing paging
                $redirect['path'] = preg_replace('#/(comments/?)?(feed|rss2?|rdf|atom)(/+|$)#', '/', $redirect['path']);
                // strip off feed endings
                $redirect['path'] = preg_replace('#/comment-page-[0-9]+?(/+)?$#', '/', $redirect['path']);
                // strip off any existing comment paging
            }
            $addl_path = '';
            if (is_feed() && in_array(get_query_var('feed'), $wp_rewrite->feeds)) {
                $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                if (!is_singular() && get_query_var('withcomments')) {
                    $addl_path .= 'comments/';
                }
                if ('rss' == get_default_feed() && 'feed' == get_query_var('feed') || 'rss' == get_query_var('feed')) {
                    $addl_path .= user_trailingslashit('feed/' . ((get_default_feed() == 'rss2') ? '' : 'rss2'), 'feed');
                } else {
                    $addl_path .= user_trailingslashit('feed/' . ((get_default_feed() == get_query_var('feed') || 'feed' == get_query_var('feed')) ? '' : get_query_var('feed')), 'feed');
                }
                $redirect['query'] = remove_query_arg('feed', $redirect['query']);
            } elseif (is_feed() && 'old' == get_query_var('feed')) {
                $old_feed_files = array('wp-atom.php' => 'atom', 'wp-commentsrss2.php' => 'comments_rss2', 'wp-feed.php' => get_default_feed(), 'wp-rdf.php' => 'rdf', 'wp-rss.php' => 'rss2', 'wp-rss2.php' => 'rss2');
                if (isset($old_feed_files[basename($redirect['path'])])) {
                    $redirect_url = get_feed_link($old_feed_files[basename($redirect['path'])]);
                    wp_redirect($redirect_url, 301);
                    die;
                }
            }
            if (get_query_var('paged') > 0) {
                $paged = get_query_var('paged');
                $redirect['query'] = remove_query_arg('paged', $redirect['query']);
                if (!is_feed()) {
                    if ($paged > 1 && !is_single()) {
                        $addl_path = ((!empty($addl_path)) ? trailingslashit($addl_path) : '') . user_trailingslashit("{$wp_rewrite->pagination_base}/{$paged}", 'paged');
                    } elseif (!is_single()) {
                        $addl_path = (!empty($addl_path)) ? trailingslashit($addl_path) : '';
                    }
                } elseif ($paged > 1) {
                    $redirect['query'] = add_query_arg('paged', $paged, $redirect['query']);
                }
            }
            if (get_option('page_comments') && ('newest' == get_option('default_comments_page') && get_query_var('cpage') > 0 || 'newest' != get_option('default_comments_page') && get_query_var('cpage') > 1)) {
                $addl_path = ((!empty($addl_path)) ? trailingslashit($addl_path) : '') . user_trailingslashit('comment-page-' . get_query_var('cpage'), 'commentpaged');
                $redirect['query'] = remove_query_arg('cpage', $redirect['query']);
            }
            $redirect['path'] = user_trailingslashit(preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/?$|', '/', $redirect['path']));
            // strip off trailing /index.php/
            if (!empty($addl_path) && $wp_rewrite->using_index_permalinks() && strpos($redirect['path'], '/' . $wp_rewrite->index . '/') === false) {
                $redirect['path'] = trailingslashit($redirect['path']) . $wp_rewrite->index . '/';
            }
            if (!empty($addl_path)) {
                $redirect['path'] = trailingslashit($redirect['path']) . $addl_path;
            }
            $redirect_url = $redirect['scheme'] . '://' . $redirect['host'] . $redirect['path'];
        }
        if ('wp-register.php' == basename($redirect['path'])) {
            if (is_multisite()) {
                /** This filter is documented in wp-login.php */
                $redirect_url = apply_filters('wp_signup_location', network_site_url('wp-signup.php'));
            } else {
                $redirect_url = site_url('wp-login.php?action=register');
            }
            wp_redirect($redirect_url, 301);
            die;
        }
    }
    // tack on any additional query vars
    $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    if ($redirect_url && !empty($redirect['query'])) {
        parse_str($redirect['query'], $_parsed_query);
        $redirect = @parse_url($redirect_url);
        if (!empty($_parsed_query['name']) && !empty($redirect['query'])) {
            parse_str($redirect['query'], $_parsed_redirect_query);
            if (empty($_parsed_redirect_query['name'])) {
                unset($_parsed_query['name']);
            }
        }
        $_parsed_query = rawurlencode_deep($_parsed_query);
        $redirect_url = add_query_arg($_parsed_query, $redirect_url);
    }
    if ($redirect_url) {
        $redirect = @parse_url($redirect_url);
    }
    // www.example.com vs example.com
    $user_home = @parse_url(home_url());
    if (!empty($user_home['host'])) {
        $redirect['host'] = $user_home['host'];
    }
    if (empty($user_home['path'])) {
        $user_home['path'] = '/';
    }
    // Handle ports
    if (!empty($user_home['port'])) {
        $redirect['port'] = $user_home['port'];
    } else {
        unset($redirect['port']);
    }
    // trailing /index.php
    $redirect['path'] = preg_replace('|/' . preg_quote($wp_rewrite->index, '|') . '/*?$|', '/', $redirect['path']);
    // Remove trailing spaces from the path
    $redirect['path'] = preg_replace('#(%20| )+$#', '', $redirect['path']);
    if (!empty($redirect['query'])) {
        // Remove trailing spaces from certain terminating query string args
        $redirect['query'] = preg_replace('#((p|page_id|cat|tag)=[^&]*?)(%20| )+$#', '$1', $redirect['query']);
        // Clean up empty query strings
        $redirect['query'] = trim(preg_replace('#(^|&)(p|page_id|cat|tag)=?(&|$)#', '&', $redirect['query']), '&');
        // Redirect obsolete feeds
        $redirect['query'] = preg_replace('#(^|&)feed=rss(&|$)#', '$1feed=rss2$2', $redirect['query']);
        // Remove redundant leading ampersands
        $redirect['query'] = preg_replace('#^\??&*?#', '', $redirect['query']);
    }
    // strip /index.php/ when we're not using PATHINFO permalinks
    if (!$wp_rewrite->using_index_permalinks()) {
        $redirect['path'] = str_replace('/' . $wp_rewrite->index . '/', '/', $redirect['path']);
    }
    // trailing slashes
    if (is_object($wp_rewrite) && $wp_rewrite->using_permalinks() && !is_404() && (!is_front_page() || is_front_page() && get_query_var('paged') > 1)) {
        $user_ts_type = '';
        if (get_query_var('paged') > 0) {
            $user_ts_type = 'paged';
        } else {
            foreach (array('single', 'category', 'page', 'day', 'month', 'year', 'home') as $type) {
                $func = 'is_' . $type;
                if (call_user_func($func)) {
                    $user_ts_type = $type;
                    break;
                }
            }
        }
        $redirect['path'] = user_trailingslashit($redirect['path'], $user_ts_type);
    } elseif (is_front_page()) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Strip multiple slashes out of the URL
    if (strpos($redirect['path'], '//') > -1) {
        $redirect['path'] = preg_replace('|/+|', '/', $redirect['path']);
    }
    // Always trailing slash the Front Page URL
    if (trailingslashit($redirect['path']) == trailingslashit($user_home['path'])) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }
    // Ignore differences in host capitalization, as this can lead to infinite redirects
    // Only redirect no-www <=> yes-www
    if (strtolower($original['host']) == strtolower($redirect['host']) || strtolower($original['host']) != 'www.' . strtolower($redirect['host']) && 'www.' . strtolower($original['host']) != strtolower($redirect['host'])) {
        $redirect['host'] = $original['host'];
    }
    $compare_original = array($original['host'], $original['path']);
    if (!empty($original['port'])) {
        $compare_original[] = $original['port'];
    }
    if (!empty($original['query'])) {
        $compare_original[] = $original['query'];
    }
    $compare_redirect = array($redirect['host'], $redirect['path']);
    if (!empty($redirect['port'])) {
        $compare_redirect[] = $redirect['port'];
    }
    if (!empty($redirect['query'])) {
        $compare_redirect[] = $redirect['query'];
    }
    if ($compare_original !== $compare_redirect) {
        $redirect_url = $redirect['scheme'] . '://' . $redirect['host'];
        if (!empty($redirect['port'])) {
            $redirect_url .= ':' . $redirect['port'];
        }
        $redirect_url .= $redirect['path'];
        if (!empty($redirect['query'])) {
            $redirect_url .= '?' . $redirect['query'];
        }
    }
    if (!$redirect_url || $redirect_url == $requested_url) {
        return false;
    }
    // Hex encoded octets are case-insensitive.
    if (false !== strpos($requested_url, '%')) {
        if (!function_exists('lowercase_octets')) {
            function lowercase_octets($matches)
            {
                return strtolower($matches[0]);
            }
        }
        $requested_url = preg_replace_callback('|%[a-fA-F0-9][a-fA-F0-9]|', 'lowercase_octets', $requested_url);
    }
    /**
     * Filter the canonical redirect URL.
     *
     * Returning false to this filter will cancel the redirect.
     *
     * @since 2.3.0
     *
     * @param string $redirect_url  The redirect URL.
     * @param string $requested_url The requested URL.
     */
    $redirect_url = apply_filters('redirect_canonical', $redirect_url, $requested_url);
    if (!$redirect_url || $redirect_url == $requested_url) {
        // yes, again -- in case the filter aborted the request
        return false;
    }
    if ($do_redirect) {
        // protect against chained redirects
        if (!redirect_canonical($redirect_url, false)) {
            wp_redirect($redirect_url, 301);
            exit;
        } else {
            // Debug
            // die("1: $redirect_url<br />2: " . redirect_canonical( $redirect_url, false ) );
            return false;
        }
    } else {
        return $redirect_url;
    }
}