RouteAccessResponseSubscriber.php

<?php

namespace Drupal\Core\EventSubscriber;

use Drupal\Core\Cache\CacheableResponseInterface;
use Drupal\Core\Routing\AccessAwareRouterInterface;
use Symfony\Component\HttpKernel\Event\ResponseEvent;
use Symfony\Component\HttpKernel\KernelEvents;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;

/**
 * Response subscriber to bubble the route's access result's cacheability.
 *
 * During routing, access checking is performed. The corresponding access result
 * is stored in the Request object's attributes, just like the matching route
 * object is. In case of a cacheable response, the route's access result also
 * determined the content of the response, and therefore the cacheability of the
 * route's access result should also be applied to the resulting response.
 *
 * @see \Drupal\Core\Routing\AccessAwareRouterInterface::ACCESS_RESULT
 * @see \Drupal\Core\Routing\AccessAwareRouter::matchRequest()
 * @see \Drupal\Core\Routing\AccessAwareRouter::checkAccess()
 */
class RouteAccessResponseSubscriber implements EventSubscriberInterface {
    
    /**
     * Bubbles the route's access result' cacheability metadata.
     *
     * @param \Symfony\Component\HttpKernel\Event\ResponseEvent $event
     *   The event to process.
     */
    public function onRespond(ResponseEvent $event) {
        if (!$event->isMainRequest()) {
            return;
        }
        $response = $event->getResponse();
        if (!$response instanceof CacheableResponseInterface) {
            return;
        }
        $request = $event->getRequest();
        $access_result = $request->attributes
            ->get(AccessAwareRouterInterface::ACCESS_RESULT);
        $response->addCacheableDependency($access_result);
    }
    
    /**
     * {@inheritdoc}
     */
    public static function getSubscribedEvents() : array {
        // Priority 10, so that it runs before FinishResponseSubscriber, which will
        // expose the cacheability metadata in the form of headers.
        $events[KernelEvents::RESPONSE][] = [
            'onRespond',
            10,
        ];
        return $events;
    }

}