Checking that the Rewrite API is available

Question

WordPress supports URL rewriting through the Rewrite API. It relies on underlying HTTP server mechanisms to get the job done.

It is not always possible for WordPress to enforce the Rewrite rules. For example, with Apache, when WordPress isn't allowed to create the .htaccess file.

The plugin I'm writing should take advantage of the Rewrite API, when it is available. Basically:

if (is_url_rewriting_available( ) ) {
    Plan A
} else {
    Plan B
}

But I can't find such function.

What I investigated so far:

• Nothing in the doc, in particular in https://codex.wordpress.org/Class_Reference/WP_Rewrite
• "Write" functions, such as flush_rewrite_rules, return nothing. So it can't be used to check the availability (eg. if (false == flush_rewrite_rules () )).
• In wp-admin/options-permalink.php, around line 130, the code checks URL rewriting requirements. However, this code doesn't seem to be reusable. Sure, I can copy/paste this code but...

Answer 1

You want WP_Rewrite::using_permalinks.

<?php
add_action('init', 'wpse142273_add_rules');
function wpse142273_add_rules()
{
    global $wp_rewrite;
    if ($wp_rewrite->using_permalinks()) {
        // Plan A
    } else {
        // Plan B
    }
}

Here's a larger example.

<?php
// inside a class somewhere
public static function url($area, $additional=null)
{
    global $wp_rewrite;

    if ($wp_rewrite->using_permalinks()) {
        $path = "/account/{$area}";

        if ($additional) {
            $path .= '/' . $additional;
        }

        if ('/' === $wp_rewrite->permalink_structure[count($wp_rewrite->permalink_structure) - 1]) {
            $path = trailingslashit($path);
        }
    } else {
        $q = array(
            static::ACCOUNT_VAR => $area,
        );

        if ($additional) {
            $q[static::ADDITIONAL_VAR] = $additional;
        }

        $path = '?'.http_build_query($q);
    }

    return apply_filters('frontend_accounts_url', home_url($path), $area, $additional);
}

Keep in mind that it's a-okay to just blindly call add_rewrite_rule when permalinks aren't in use. You'll need to add custom query variables anyway (by filtering query_vars) so you plugin/theme can still work just fine without rewrites.