How to issue 404 from a KernelEvents::REQUEST event

Question

I'm trying to issue a 404 from a KernelEvents::REQUEST event, but it's resulting in the following error:

Fatal error: Maximum function nesting level of '256' reached, aborting! in /var/www/vendor/symfony/http-foundation/HeaderBag.php on line 162

Here's my class

<?php

namespace Drupal\my_module\EventSubscriber;

use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpKernel\Event\GetResponseEvent;
use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;
use Symfony\Component\HttpKernel\KernelEvents;

class MyClass implements EventSubscriberInterface {

  /**
   * {@inheritdoc}
   */
  static function getSubscribedEvents() {
    $events[KernelEvents::REQUEST][] = ['my404Check'];

    return $events;
  }

  public function my404Check(GetResponseEvent $event) {
    // Do some logic here to check if it should be a 404.
    throw new NotFoundHttpException();
  }

}

I'm guessing I can't throw exceptions here, but can't see any other documentation on how to issue the 404.

Answer 1

You can set a response early in a request event:

 public function my404Check(RequestEvent $event) {

    // only return a response for a master request
    if (!$event->isMainRequest()) {
      return;
    }

    // Do some logic here to check if it should be a 404.

    $response = new Response('', Response::HTTP_NOT_FOUND);
    $event->setResponse($response);
  }

The event dispatcher checks if a response is already set and returns this response without executing any more code to build a Drupal response.

(Code updated for D9/10)

Answer 2

I would like to post another solution, that I have found in the Rabbit Hole module:

public function my404Check(GetResponseEvent $event) {
  // Don't process events with HTTP exceptions - those have either been thrown
  // by us or have nothing to do with this module.
  if ($event->getRequest()->get('exception') != NULL) {
    return;
  }

  // Do some logic here to check if it should be a 404.

  $response = new Response('', Response::HTTP_NOT_FOUND);
  $event->setResponse($response);
}

The event dispatcher skips processing if request has an exception already. In addition you can check the exception type.

Answer 3

I know this is old, but in case someone else finds this... setting the response was not enough for me, I still ended up with the same 'fast 404' error page, even when checking for the master request (I cleared cache). I also would prefer to simply throw the NotFoundHttpException like anywhere else in my code rather than create the response manually.

With this approach, I simply 'transform' the exception I'm catching from the event into a the NotFoundHttpException. Note that I use a priority higher than core's ExceptionLoggingSubscriber to avoid double logging of the exception.

  /**
   * {@inheritdoc}
   *
   * Use priority > 50 to run before core's ExceptionLoggingSubscriber.
   */
  public static function getSubscribedEvents() {
    $events[KernelEvents::EXCEPTION][] = ['onException', 60];
    return $events;
  }

  /**
   * Return a 404.
   *
   * @param GetResponseForExceptionEvent $event
   */
  public function onException(GetResponseForExceptionEvent $event) {
    $e = $event->getException();
    if ({{CUSTOM LOGIC HERE}}) {
      $new_exception = new NotFoundHttpException($e->getMessage());
      $event->setException($new_exception);
    }
  }