Adding Mod Rewrite Rules Programmatically in WordPress Plugin

The following sample plugin adds the custom mod rewrite rules to .htaccess when the user changes the permalink settings.

/* Plugin Name: Sample Mod Rewrite  */

add_action('generate_rewrite_rules', array(new custom_mod_rewrite, "generate_rewrite_rules"));

class custom_mod_rewrite {
    function __construct() {
        $this->wp_rewrite = & $GLOBALS["wp_rewrite"];
    }
    function generate_rewrite_rules() {

        $non_wp_rules = array(
            'simple-redirect/?$plugin_name' => 'http://google.com',
            'one-more-redirect/?$plugin_name' => 'http://yahoo.com'
        );

        $this->wp_rewrite->non_wp_rules = $non_wp_rules + $this->wp_rewrite->non_wp_rules;
        add_filter('mod_rewrite_rules', array(&$this, "mod_rewrite_rules"));
    }
    function mod_rewrite_rules($rules) {
        return preg_replace('#^(RewriteRule ^.*/)?$plugin_name .*(http://.*) [QSA,L]#mi', '$1 $2 [R=301,L]', $rules);
    }
}

There are two problems I found with this.

1. If it is set to the default permalink, it won’t add the rules.
2. More importantly, unless the user changes the permalink settings, the rules won’t be added. (can be solved with $wp_rewrite->flush_rules() performed at the plugin activation)

For #2, I’m wondering if there is a good way to add the rules programmatically.

IIS (common on Windows servers) does not support mod_rewrite.

source: http://codex.wordpress.org/Using_Permalinks#Permalinks_without_mod_rewrite

It sounds like not all systems use .htaccess. So directly editing the .htaccess file may not be the best choice for a distributed plugin. I don’t know. Probably I have to check if the server uses Apache and if so I need to check whether .htacess is writable and existing rules do not have the adding rules, then at last I can append the rules to it. Also when the user deactivate the plugin, the rules have to be erased. So it’s kind of troublesome.

If WordPress can handle it with a built-in API or something, I’d like to leave it to WordPress. But the above example was what I could have found so far. So I appreciate your information.

Update

As pfefferle suggested, I could use $wp_rewrite->flush_rules(). However, the problem #1 still persists; it won’t take any effect when the default permalink settings is used. Any ideas?

/* Plugin Name: Sample Mod Rewrite  */

$custom_mod_rewrite = new custom_mod_rewrite;
register_activation_hook( __FILE__, array($custom_mod_rewrite, 'flush_rewrite_rules'));
register_deactivation_hook( __FILE__, array($custom_mod_rewrite, 'flush_rewrite_rules'));
add_action('generate_rewrite_rules', array($custom_mod_rewrite, "generate_rewrite_rules"));

class custom_mod_rewrite {
    function __construct() {
        $this->wp_rewrite = & $GLOBALS["wp_rewrite"];
    }
    function flush_rewrite_rules() {
        $this->wp_rewrite->flush_rules();
    }
    function generate_rewrite_rules() {

        $non_wp_rules = array(
            'simple-redirect/?$plugin_name' => 'http://google.com',
            'one-more-redirect/?$plugin_name' => 'http://yahoo.com'
        );

        $this->wp_rewrite->non_wp_rules = $non_wp_rules + $this->wp_rewrite->non_wp_rules;
        add_filter('mod_rewrite_rules', array(&$this, "mod_rewrite_rules"));
    }
    function mod_rewrite_rules($rules) {
        return preg_replace('#^(RewriteRule ^.*/)?$plugin_name .*(http://.*) [QSA,L]#mi', '$1 $2 [R=301,L]', $rules);
    }
}

Also, when deactivating the plugin, it doesn’t change back to the previous rules. I just followed the codex example and just set it to flush the rules when deactivating the plugin. So there should be some code to delete the added rules.

As a side note, according to the codex,

Flushing the rewrite rules is an expensive operation, … … you should flush rewrite rules on the activation hook of a plugin, or when you know that the rewrite rules need to be changed

Remaining Issues:

1. If it is set to the default permalink, it won’t add the rules.
2. When deactivating the plugin, it doesn’t change back to the previous rules.