A Fix for a WordPress Paging Problem

I recently discovered a problem in the next/previous paging links of a custom WordPress 2.2.1 site we created for Fractional Jets Focus. When viewing a list of articles by category, the previous posts link generated a 404 error.

After digging for too long through WordPress code and Google search results, I found that the problem was related to an apparent bug or conflict between the paging feature and custom permalinks.

Our custom permalink setting in Options -> Permalinks is this:

/%category%/%year%/%monthnum%/%postname%/

When you want to view all the posts for a certain category, an example URL is /blog/2007/9/. The problem is that the URL generated by next_posts_link() was misinterpreted by WordPress because of the permalink. The link was: /blog/2007/9/page/2/. Unfortunately, the string "page" in this URL was interpreted as a post name, instead of a token for the page index.

There is probably some voodoo I could have done in the .htaccess file with mod_rewrite to fix the issue, but I feared breaking something else. So, I wrote the following plugin. It's so short that I'm publishing the whole thing inline.

<?php
/*
Plugin Name: Fix Paging in Category Listings 
Plugin URI: http://www.thinkbarefoot.com
Description: Fixes a bug where next/previous links are broken in category by year/month listings
Version: 0.5
Author: Doug Smith
Author URI: http://www.thinkbarefoot.com

Copyright 2007  Doug Smith  (email: dsmith@thinkbarefoot.com)

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

*/

/**
 * Function to fix problem where next/previous buttons are broken on list
 * of posts in a category when the custom permalink string is:
 * /%category%/%year%/%monthnum%/%postname%/ 
 * The problem is that with a url like this:
 * 
 * /category/2007/10/page/2
 * 
 * the 'page' looks like a post name, not the keyword "page"
 */
function remove_page_from_query_string($query_string)
{ 
    if ($query_string['name'] == 'page' && isset($query_string['page'])) {
        unset($query_string['name']);
        // 'page' in the query_string looks like '/2', so split it out
        list($delim, $page_index) = split('/', $query_string['page']);
        $query_string['paged'] = $page_index;
    }      
    return $query_string;
}

add_filter('request', 'remove_page_from_query_string');

?>

This plugin simply checks to see whether the post name is 'page', and if there is a 'page' parameter too. If so, it removes the 'name', and assigns the page index to the magic 'paged' parameter. Paging restored.

Doug Smith, Senior Developer, Barefoot