EarlyRenderingControllerWrapperSubscriber.php

<?php

namespace Drupal\Core\EventSubscriber;

use Drupal\Core\Ajax\AjaxResponse;
use Drupal\Core\Cache\CacheableDependencyInterface;
use Drupal\Core\Cache\CacheableResponseInterface;
use Drupal\Core\Render\AttachmentsInterface;
use Drupal\Core\Render\BubbleableMetadata;
use Drupal\Core\Render\RenderContext;
use Drupal\Core\Render\RendererInterface;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\HttpKernel\Controller\ArgumentResolverInterface;
use Symfony\Component\HttpKernel\Event\ControllerEvent;
use Symfony\Component\HttpKernel\KernelEvents;

/**
 * Subscriber that wraps controllers, to handle early rendering.
 *
 * When controllers call 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
 * ::renderInIsolation() methods. In that case, no bubbleable metadata is lost.
 *
 * If the render context is not empty, then the controller did use
 * RendererInterface::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.
 *
 * @see \Drupal\Core\Render\RendererInterface
 * @see \Drupal\Core\Render\Renderer
 *
 * @todo Remove in Drupal 9.0.0, by disallowing early rendering.
 */
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, $arguments);
        });
        // If early rendering happened, i.e. if code in the controller called
        // RendererInterface::render() outside of a render context, then the
        // bubbleable metadata for that is stored in the current render context.
        if (!$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 CacheableResponseInterface) {
                $response->addCacheableDependency($early_rendering_bubbleable_metadata);
            }
            elseif ($response instanceof AttachmentsInterface || $response instanceof CacheableDependencyInterface) {
                throw new \LogicException(sprintf('The controller result claims to be providing relevant cache metadata, but leaked metadata was detected. Ensure you are not rendering content too early. Returned object class: %s.', get_class($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() : array {
        $events[KernelEvents::CONTROLLER][] = [
            'onController',
        ];
        return $events;
    }

}