root/tags/1.3/wp-includes/canonical.php

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

function redirect_canonical($requested_url=NULL, $do_redirect=true) {
    global $wp_rewrite, $posts, $is_IIS;

    if ( is_feed() || is_trackback() || is_search() || is_comments_popup() || is_admin() || $is_IIS || ( isset($_POST) && count($_POST) ) || is_preview() )
        return;

    if ( !$requested_url ) {
        // build the URL in the address bar
        $requested_url  = ( isset($_SERVER['HTTPS'] ) && strtolower($_SERVER['HTTPS']) == 'on' ) ? '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
    $original['path'] = preg_replace('|/index\.php$|', '/', $original['path']);

    $redirect = $original;
    $redirect_url = false;

    // These tests give us a WP-generated permalink
    if ( is_404() ) {
        $redirect_url = redirect_guess_404_permalink();
    } elseif ( is_object($wp_rewrite) && $wp_rewrite->using_permalinks() ) {
        // rewriting of old ?p=X, ?m=2004, ?m=200401, ?m=20040101
        if ( is_single() && isset($_GET['p']) ) {
            if ( $redirect_url = get_permalink(get_query_var('p')) )
                $redirect['query'] = remove_query_arg('p', $redirect['query']);
        } elseif ( is_page() && isset($_GET['page_id']) ) {
            if ( $redirect_url = get_permalink(get_query_var('page_id')) )
                $redirect['query'] = remove_query_arg('page_id', $redirect['query']);
        } elseif ( isset($_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', $redirect['query']);
        // now moving on to non ?m=X year/month/day links
        } elseif ( is_day() && get_query_var('year') && get_query_var('monthnum') && isset($_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'), $redirect['query']);
        } elseif ( is_month() && get_query_var('year') && isset($_GET['monthnum']) ) {
            if ( $redirect_url = get_month_link(get_query_var('year'), get_query_var('monthnum')) )
                $redirect['query'] = remove_query_arg(array('year', 'monthnum'), $redirect['query']);
        } elseif ( is_year() && isset($_GET['year']) ) {
            if ( $redirect_url = get_year_link(get_query_var('year')) )
                $redirect['query'] = remove_query_arg('year', $redirect['query']);
        } elseif ( is_category() && isset($_GET['cat']) ) {
            if ( $redirect_url = get_category_link(get_query_var('cat')) )
                $redirect['query'] = remove_query_arg('cat', $redirect['query']);
        } elseif ( is_author() && isset($_GET['author']) ) {
            $author = get_userdata(get_query_var('author'));
            if ( false !== $author && $redirect_url = get_author_link(false, $author->ID, $author->user_nicename) )
                $redirect['query'] = remove_query_arg('author', $redirect['author']);
        }

    // paging
        if ( $paged = get_query_var('paged') ) {
            if ( $paged > 0 ) {
                if ( !$redirect_url )
                    $redirect_url = $requested_url;
                $paged_redirect = @parse_url($redirect_url);
                $paged_redirect['path'] = preg_replace('|/page/[0-9]+?(/+)?$|', '/', $paged_redirect['path']); // strip off any existing paging
                $paged_redirect['path'] = preg_replace('|/index.php/?$|', '/', $paged_redirect['path']); // strip off trailing /index.php/
                if ( $paged > 1 && !is_single() ) {
                    $paged_redirect['path'] = trailingslashit($paged_redirect['path']);
                    if ( $wp_rewrite->using_index_permalinks() && strpos($paged_redirect['path'], '/index.php/') === false )
                        $paged_redirect['path'] .= 'index.php/';
                    $paged_redirect['path'] .= user_trailingslashit("page/$paged", 'paged');
                } elseif ( !is_home() && !is_single() ){
                    $paged_redirect['path'] = user_trailingslashit($paged_redirect['path'], 'paged');
                }
                $redirect_url = $paged_redirect['scheme'] . '://' . $paged_redirect['host'] . $paged_redirect['path'];
                $redirect['path'] = $paged_redirect['path'];
            }
            $redirect['query'] = remove_query_arg('paged', $redirect['query']);
        }
    }

    // tack on any additional query vars
    if ( $redirect_url && $redirect['query'] ) {
        if ( strpos($redirect_url, '?') !== false )
            $redirect_url .= '&';
        else
            $redirect_url .= '?';
        $redirect_url .= $redirect['query'];
    }

    if ( $redirect_url )
        $redirect = @parse_url($redirect_url);

    // www.example.com vs example.com
    $user_home = @parse_url(get_option('home'));
    $redirect['host'] = $user_home['host'];

    // Handle ports
    if ( isset($user_home['port']) )
        $redirect['port'] = $user_home['port'];
    else
        unset($redirect['port']);

    // trailing /index.php/
    $redirect['path'] = preg_replace('|/index.php/$|', '/', $redirect['path']);

    // strip /index.php/ when we're not using PATHINFO permalinks
    if ( !$wp_rewrite->using_index_permalinks() )
        $redirect['path'] = str_replace('/index.php/', '/', $redirect['path']);

    // trailing slashes
    if ( is_object($wp_rewrite) && $wp_rewrite->using_permalinks() && !is_404() && (!is_home() || ( is_home() && (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') 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_home() ) {
        $redirect['path'] = trailingslashit($redirect['path']);
    }

    // Always trailing slash the 'home' URL
    if ( $redirect['path'] == $user_home['path'] )
        $redirect['path'] = trailingslashit($redirect['path']);

    // Ignore differences in host capitalization, as this can lead to infinite redirects
    if ( strtolower($original['host']) == strtolower($redirect['host']) )
        $redirect['host'] = $original['host'];

    if ( array($original['host'], $original['port'], $original['path'], $original['query']) !== array($redirect['host'], $redirect['port'], $redirect['path'], $redirect['query']) ) {
        $redirect_url = $redirect['scheme'] . '://' . $redirect['host'];
        if ( isset($redirect['port']) )
             $redirect_url .= ':' . $redirect['port'];
        $redirect_url .= $redirect['path'];
        if ( $redirect['query'] )
            $redirect_url .= '?' . $redirect['query'];
    }

    if ( $redirect_url && $redirect_url != $requested_url ) {
        // var_dump($redirect_url); die();
        $redirect_url = apply_filters('redirect_canonical', $redirect_url, $requested_url);
        if ( $do_redirect) {
            // protect against chained redirects
            if ( !redirect_canonical($redirect_url, false) ) {
                wp_redirect($redirect_url, 301);
                exit();
            } else {
                return false;
            }
        } else {
            return $redirect_url;
        }
    } else {
        return false;
    }
}

function redirect_guess_404_permalink() {
    global $wp_query, $wpdb;
    if ( !get_query_var('name') )
        return false;

    $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);
}

add_action('template_redirect', 'redirect_canonical');

?>