Custom URL Rewrite Rules not working

Question

I added the following custom routes to WordPress:

function add_custom_rewrite_rules() {
    add_rewrite_rule( 'generate/?', 'index.php?custom_route=generate', 'top' );
    add_rewrite_rule( 'random/?', 'index.php?custom_route=random', 'top' );
}

add_action( 'init', 'add_custom_rewrite_rules', PHP_INT_MAX );

This is the callback function:

function custom_routes_handler() {

    $custom_route = get_query_var( 'custom_route' );

    var_dump( $custom_route);

    global $wp_rewrite;

    foreach ( $wp_rewrite->rewrite_rules() as $rule => $rewrite ) {
        echo $rule . ' => ' . $rewrite . '<br>';
    }
    exit;

}

I get the var_dump result of string(0) "". And in the listed routes I can see, among all other routes:

generate/?$ => index.php?custom_route=generate
random/?$ => index.php?custom_route=random

I also triggered the URL rewrites regeneration via Admin > Settings > Save permalinks.

The WordPress installation is in the root folder.

Why am I not getting the proper value for get_query_var( 'custom_route' )?

Answer 1

I encountered the same issue on a client project. If you haven't already, you'll need to add the query variable as a public query variable otherwise using get_query_var() won't work properly.

/**
 * Adds the query var to public vars, making it accessible.
 */
add_filter('query_vars', 'query_vars');
function query_vars($public_query_vars)
{
    $public_query_vars[] = 'custom_route';
    return $public_query_vars;
}

Using this filter will add custom_route to the public query variables, and you should be able to get it's value in your script.

For further reference: https://developer.wordpress.org/reference/hooks/query_vars/