Ticket #4554: canonical.php

<?php
// Based on "Permalink Redirect" from Scott Yang and "Enforce www. Preference" by Mark Jaquith

function redirect_permalinks() {
        global $withcomments;

        $requested = @parse_url( $_SERVER['REQUEST_URI'] );
        if ( false === $requested )
                return;

        $requested = $requested['path'];
        $requested_scheme = ( isset($_SERVER['HTTPS'] ) && strtolower($_SERVER['HTTPS']) == 'on' ) ? 'https://' : 'http://';

        if ( is_feed() || is_trackback() || is_search() || is_comments_popup() )
                return;

        $link = redirect_guess_permalink();
        if ( !$link )
                return;
        $permalink = @parse_url( $link );

        // WP2.1: If a static page has been set as the front-page, we'll get 
        // empty string here.
        if ( !$permalink['path'] )
                $permalink['path'] = '/';

        if ( $requested != $permalink['path'] ) {
                $redirect = $link;
        } else {
                $user_home = parse_url(get_option('home'));

                $user_home['scheme'] . '://' . $user_home['host'];

                if ( $user_home['host'] != $_SERVER['HTTP_HOST'] )
                        $redirect = $requested_scheme . $user_home['host'] . $_SERVER['REQUEST_URI'];
        }

        if ( $redirect ) {
                wp_redirect($redirect, 301);
                exit();
        }
}

function redirect_guess_permalink() {
        global $posts;

        // For partial links
        if ( is_404() ) {
                global $wp_query, $wpdb;
                if ( !get_query_var( 'name' ) )
                        return;

                $where = "post_name LIKE '" . $wpdb->escape( get_query_var( 'name' ) ) . "%'";

                // if any of year, monthnum, or day are set, use them to refine the query
                if ( get_query_var('year') )
                        $where .= " AND YEAR(post_date) = '" . $wpdb->escape(get_query_var('year')) . "'";
                if ( get_query_var('monthnum') )
                        $where .= " AND MONTH(post_date) = '" . $wpdb->escape(get_query_var('monthnum')) . "'";
                if ( get_query_var('day') )
                        $where .= " AND DAYOFMONTH(post_date) = '" . $wpdb->escape(get_query_var('day')) . "'";

                $post_id = $wpdb->get_var( "SELECT ID FROM $wpdb->posts WHERE $where AND post_status = 'publish'" );
                if ( !$post_id )
                        return false;
                return get_permalink( $post_id );
        }

        $haspost = count( $posts ) > 0;
        if ( get_query_var('m') ) {
                // Handling special case with '?m=yyyymmddHHMMSS'
                // Since there is no code for producing the archive links for
                // is_time, we will give up and not trying any redirection.
                $m = preg_replace( '/[^0-9]/', '', get_query_var('m') );
                switch ( strlen($m) ) {
                        case 4: // Yearly
                                $link = get_year_link($m);
                                break;
                        case 6: // Monthly
                                $link = get_month_link( substr($m, 0, 4), substr($m, 4, 2) );
                                break;
                        case 8: // Daily
                                $link = get_day_link(substr($m, 0, 4), substr($m, 4, 2), substr($m, 6, 2));
                                break;
                        default:
                                return false;
                }
        } elseif ( ( is_single() || is_page() ) && ( sizeof( $posts ) > 0 ) ) {
                $post = $posts[0];
                $link = get_permalink($post->ID);
                $page = get_query_var('page');
                if ( $page && $page > 1 )
                        $link = trailingslashit( $link ) . user_trailingslashit($page);
        } elseif ( is_author() && $haspost ) {
                global $wp_version;
                if ( $wp_version >= '2' ) {
                        $author = get_userdata(get_query_var('author'));
                        if ( false === $author )
                                return false;
                        $link = get_author_link( false, $author->ID, $author->user_nicename );
                } else {
                        // XXX: get_author_link() bug in WP 1.5.1.2
                        //      s/author_nicename/user_nicename/
                        global $cache_userdata;
                        $userid = get_query_var('author');
                        $link = get_author_link(false, $userid,
                                $cache_userdata[$userid]->user_nicename);
                }
        } elseif ( is_category() && $haspost ) {
                $link = get_category_link(get_query_var('cat'));
        } elseif ( is_day() && $haspost ) {
                $link = get_day_link(get_query_var('year'),
                                                         get_query_var('monthnum'),
                                                         get_query_var('day'));
        } elseif (is_month() && $haspost) {
                $link = get_month_link(get_query_var('year'),
                                                           get_query_var('monthnum'));
        } elseif (is_year() && $haspost) {
                $link = get_year_link(get_query_var('year'));
        } elseif ( is_home() ) {
                // WP2.1. Handling "Posts page" option. 
                if ((get_option('show_on_front') == 'page') &&
                        ($reqpage = get_option('page_for_posts'))) 
                {
                        $link = get_permalink($reqpage);
                } else {
                        $link = trailingslashit(get_settings('home'));
                }
        } else {
                return false;
        }

        if ( is_paged() ) {
                $paged = get_query_var('paged');
                if ($paged)
                        $link = trailingslashit($link) . user_trailingslashit("page/$paged");
        }

        return $link;
}

add_action('template_redirect', 'redirect_permalinks');

?>