[WordPress] 画像のリンク先を強制的に添付ファイル投稿URLに変更する奴

attachment_link_convert.php

<?php
function attachment_link_convert($content){
    global $wpdb;
    $upload_dir = wp_upload_dir();
    $pattern = '#(<a [^>]*href=[\'"])('.preg_quote($upload_dir['baseurl']).'/)([^\'"]*)([\'"][^>]*><img [^>]*></a>)#uism';
    if ( preg_match_all($pattern, $content, $matches, PREG_SET_ORDER) ) {
        foreach ( $matches as $match ) {
            $attachment_id = $wpdb->get_var($wpdb->prepare("
                select p.ID
                  from {$wpdb->posts} as p
                 inner join {$wpdb->postmeta} as m on p.ID = m.post_id
                 where m.meta_key = %s
                   and m.meta_value = %s
                 limit 1",
                '_wp_attached_file',
                $match[3]));
            if ( $attachment_id ) {
                $attachment_url = get_attachment_link($attachment_id);
                $new_link = $match[1].$attachment_url.$match[4];
                $content = str_replace($match[0], $new_link, $content);
            }
        }
    }
    unset ($matches);
    return $content;
}
add_filter('the_content','attachment_link_convert');