EnhancerInterface.php

<?php

namespace Drupal\Core\Routing;

use Symfony\Component\HttpFoundation\Request;

/**
 * A route enhance service to determine route enhance rules.
 */
interface EnhancerInterface {
    
    /**
     * Updates the defaults for a route definition based on the request.
     *
     * @param array $defaults
     *   The defaults, maps to '_defaults' in the route definition YAML.
     * @param \Symfony\Component\HttpFoundation\Request $request
     *   The Request instance.
     *
     * @return array
     *   The modified defaults. Each enhancer MUST return the
     *   $defaults but may add or remove values.
     */
    public function enhance(array $defaults, Request $request);

}