February 12, 2011 
Definition:
function redirect_canonical( $requested_url = null, $do_redirect = true ) {}
Redirects incoming links to the proper URL based on the site url.
Search engines consider http://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.
Parameters
- string $requested_url: Optional. The URL that was requested, used to figure if redirect is needed.
- bool $do_redirect: Optional. Redirect to the new URL.
Return values
returns:Null, if redirect not needed. False, if redirect not needed or the string of the URL
Defined filters
- redirect_canonical
apply_filters('redirect_canonical', $redirect_url, $requested_url)
Source code
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() || $is_IIS )
return;
if ( !$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_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_query_arg(array('p', 'page_id', 'attachment_id', 'post_type'), $redirect['query']);
}
}
// 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_query_arg(array('p', 'page_id', 'attachment_id', 'post_type'), $redirect['query']);
}
}
if ( ! $redirect_url )
$redirect_url = redirect_guess_404_permalink();
} elseif ( is_object($wp_rewrite) && $wp_rewrite->using_permalinks() ) {
// rewriting of old ?p=X, ?m=2004, ?m=200401, ?m=20040101
if ( is_attachment() && !empty($_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 ) {
$category = get_category_by_path(get_query_var('category_name'));
$post_terms = wp_get_object_terms($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') && $redirect_url ) {
$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 ( 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'] );
}
$redirect['path'] = user_trailingslashit( preg_replace('|/index.php/?$|', '/', $redirect['path']) ); // strip off trailing /index.php/
if ( !empty( $addl_path ) && $wp_rewrite->using_index_permalinks() && strpos($redirect['path'], '/index.php/') === false )
$redirect['path'] = trailingslashit($redirect['path']) . 'index.php/';
if ( !empty( $addl_path ) )
$redirect['path'] = trailingslashit($redirect['path']) . $addl_path;
$redirect_url = $redirect['scheme'] . '://' . $redirect['host'] . $redirect['path'];
}
}
// 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_map( 'rawurlencode', $_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
$redirect['path'] = preg_replace('|/index.php/*?$|', '/', $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$3', $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('/index.php/', '/', $redirect['path']);
// trailing slashes
if ( is_object($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);
}
// Note that you can use the "redirect_canonical" filter to cancel a canonical redirect for whatever reason by returning FALSE
$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;
}
}
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