class EarlyRenderingControllerWrapperSubscriber in Drupal 9

Subscriber that wraps controllers, to handle early rendering.

When controllers call drupal_render() (RendererInterface::render()) outside of a render context, we call that "early rendering". Controllers should return only render arrays, but we cannot prevent controllers from doing early rendering. The problem with early rendering is that the bubbleable metadata (cacheability & attachments) are lost.

This can lead to broken pages (missing assets), stale pages (missing cache tags causing a page not to be invalidated) or even security problems (missing cache contexts causing a cached page not to be varied sufficiently).

This event subscriber wraps all controller executions in a closure that sets up a render context. Consequently, any early rendering will have their bubbleable metadata (assets & cacheability) stored on that render context.

If the render context is empty, then the controller either did not do any rendering at all, or used the RendererInterface::renderRoot() or ::renderPlain() methods. In that case, no bubbleable metadata is lost.

If the render context is not empty, then the controller did use drupal_render(), and bubbleable metadata was collected. This bubbleable metadata is then merged onto the render array.

In other words: this just exists to ease the transition to Drupal 8: it allows controllers that return render arrays (the majority) and \Drupal\Core\Ajax\AjaxResponse\AjaxResponse objects (a sizable minority that often involve a fair amount of rendering) to still do early rendering. But controllers that return any other kind of response are already expected to do the right thing, so if early rendering is detected in such a case, an exception is thrown.

@todo Remove in Drupal 9.0.0, by disallowing early rendering.

Hierarchy

• class \Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber implements \Symfony\Component\EventDispatcher\EventSubscriberInterface

See also

\Drupal\Core\Render\RendererInterface

\Drupal\Core\Render\Renderer

1 string reference to 'EarlyRenderingControllerWrapperSubscriber'

core.services.yml in core/core.services.yml

core/core.services.yml

1 service uses EarlyRenderingControllerWrapperSubscriber

early_rendering_controller_wrapper_subscriber in core/core.services.yml

Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber

File

core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php, line 55

Namespace

Drupal\Core\EventSubscriber

class EarlyRenderingControllerWrapperSubscriber implements EventSubscriberInterface {

  /**
   * The argument resolver.
   *
   * @var \Symfony\Component\HttpKernel\Controller\ArgumentResolverInterface
   */
  protected $argumentResolver;

  /**
   * The renderer.
   *
   * @var \Drupal\Core\Render\RendererInterface
   */
  protected $renderer;

  /**
   * Constructs a new EarlyRenderingControllerWrapperSubscriber instance.
   *
   * @param \Symfony\Component\HttpKernel\Controller\ArgumentResolverInterface $argument_resolver
   *   The argument resolver.
   * @param \Drupal\Core\Render\RendererInterface $renderer
   *   The renderer.
   */
  public function __construct(ArgumentResolverInterface $argument_resolver, RendererInterface $renderer) {
    $this->argumentResolver = $argument_resolver;
    $this->renderer = $renderer;
  }

  /**
   * Ensures bubbleable metadata from early rendering is not lost.
   *
   * @param \Symfony\Component\HttpKernel\Event\ControllerEvent $event
   *   The controller event.
   */
  public function onController(ControllerEvent $event) {
    $controller = $event
      ->getController();

    // See \Symfony\Component\HttpKernel\HttpKernel::handleRaw().
    $arguments = $this->argumentResolver
      ->getArguments($event
      ->getRequest(), $controller);
    $event
      ->setController(function () use ($controller, $arguments) {
      return $this
        ->wrapControllerExecutionInRenderContext($controller, $arguments);
    });
  }

  /**
   * Wraps a controller execution in a render context.
   *
   * @param callable $controller
   *   The controller to execute.
   * @param array $arguments
   *   The arguments to pass to the controller.
   *
   * @return mixed
   *   The return value of the controller.
   *
   * @throws \LogicException
   *   When early rendering has occurred in a controller that returned a
   *   Response or domain object that cares about attachments or cacheability.
   *
   * @see \Symfony\Component\HttpKernel\HttpKernel::handleRaw()
   */
  protected function wrapControllerExecutionInRenderContext($controller, array $arguments) {
    $context = new RenderContext();
    $response = $this->renderer
      ->executeInRenderContext($context, function () use ($controller, $arguments) {

      // Now call the actual controller, just like HttpKernel does.
      return call_user_func_array($controller, $arguments);
    });

    // If early rendering happened, i.e. if code in the controller called
    // drupal_render() outside of a render context, then the bubbleable metadata
    // for that is stored in the current render context.
    if (!$context
      ->isEmpty()) {

      /** @var \Drupal\Core\Render\BubbleableMetadata $early_rendering_bubbleable_metadata */
      $early_rendering_bubbleable_metadata = $context
        ->pop();

      // If a render array or AjaxResponse is returned by the controller, merge
      // the "lost" bubbleable metadata.
      if (is_array($response)) {
        BubbleableMetadata::createFromRenderArray($response)
          ->merge($early_rendering_bubbleable_metadata)
          ->applyTo($response);
      }
      elseif ($response instanceof AjaxResponse) {
        $response
          ->addAttachments($early_rendering_bubbleable_metadata
          ->getAttachments());

        // @todo Make AjaxResponse cacheable in
        //   https://www.drupal.org/node/956186. Meanwhile, allow contrib
        //   subclasses to be.
        if ($response instanceof CacheableResponseInterface) {
          $response
            ->addCacheableDependency($early_rendering_bubbleable_metadata);
        }
      }
      elseif ($response instanceof AttachmentsInterface || $response instanceof CacheableResponseInterface || $response instanceof CacheableDependencyInterface) {
        throw new \LogicException(sprintf('The controller result claims to be providing relevant cache metadata, but leaked metadata was detected. Please ensure you are not rendering content too early. Returned object class: %s.', get_class($response)));
      }
      else {

        // A Response or domain object is returned that does not care about
        // attachments nor cacheability; for instance, a RedirectResponse. It is
        // safe to discard any early rendering metadata.
      }
    }
    return $response;
  }

  /**
   * {@inheritdoc}
   */
  public static function getSubscribedEvents() {
    $events[KernelEvents::CONTROLLER][] = [
      'onController',
    ];
    return $events;
  }

}

Members

Name	Modifiers	Type	Description	Overrides
EarlyRenderingControllerWrapperSubscriber::$argumentResolver	protected	property	The argument resolver.
EarlyRenderingControllerWrapperSubscriber::$renderer	protected	property	The renderer.
EarlyRenderingControllerWrapperSubscriber::getSubscribedEvents	public static	function
EarlyRenderingControllerWrapperSubscriber::onController	public	function	Ensures bubbleable metadata from early rendering is not lost.
EarlyRenderingControllerWrapperSubscriber::wrapControllerExecutionInRenderContext	protected	function	Wraps a controller execution in a render context.
EarlyRenderingControllerWrapperSubscriber::__construct	public	function	Constructs a new EarlyRenderingControllerWrapperSubscriber instance.