Reputation: 2632

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.

If it is set to the default permalink, it won't add the rules.
~~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: