How do I redirect in a class sub-classing the EventSubscriber class?

Question

I want to redirect to a specific URL in an EventSubscriber class instead of showing the Page not found page. I followed Symfony2 redirect for event listener? but the redirect goes to the home.

This is the code I am using.

use Drupal\Core\Url;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\HttpFoundation\RedirectResponse;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\HttpKernel\Event\GetResponseEvent;
use Symfony\Component\HttpKernel\KernelEvents;

class PageNotFound implements EventSubscriberInterface {
  public function pageNotFound(GetResponseEvent $event) {
    $request = $event->getRequest();
    $id = '1234';
    $scheme_and_http_host = $request->getSchemeAndHttpHost();
    $url = Url::fromRoute('myroute', ['id' => $id])->toString(); // this url exist (checked)

    $response = new RedirectResponse($scheme_and_http_host . $url, Response::HTTP_MOVED_PERMANENTLY);
    $event->setResponse($response);
  }

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

mymodule.services.yml

services:
  mymodule.page_not_found:
    class: Drupal\mymodule\EventListener\PageNotFound
    tags:
      - {name: event_subscriber}

How do I redirect users from an EventSubscriber class?

Answer 1

To catch a 404 exception you need to subscribe to a KernelEvents::EXCEPTION event. As there is already a base class for html exceptions you don't need to code this yourself. You can simply put the code in an on404() method of a class that extends HttpExceptionSubscriberBase:

Utility base class for exception subscribers.

A subscriber may extend this class and implement getHandledFormats() to indicate which request formats it will respond to. Then implement an on*() method for any error code (HTTP response code) that should be handled. For example, to handle 404 Not Found messages add a method:

public function on404(GetResponseForExceptionEvent $event) {}

That method should then call $event->setResponse() to set the response object for the exception. Alternatively, it may opt not to do so and then other listeners will have the opportunity to handle the exception.