Drupal Event Subscribers

Example (Best Practice)

// src/EventSubscriber/MyEventSubscriber.php
namespace Drupal\my_module\EventSubscriber;

use Drupal\Core\Session\AccountProxyInterface;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\HttpKernel\Event\RequestEvent;
use Symfony\Component\HttpKernel\KernelEvents;

final class MyEventSubscriber implements EventSubscriberInterface {

  public function __construct(
    private readonly AccountProxyInterface $currentUser,
  ) {}

  public static function getSubscribedEvents(): array {
    return [
      // Note: Higher priority runs earlier. Default is 0.
      KernelEvents::REQUEST => ['onRequest', 100],
    ];
  }

  public function onRequest(RequestEvent $event): void {
    if (!$event->isMainRequest()) {
      return;
    }

    if (!$this->currentUser->isAuthenticated()) {
      return;
    }

    // Example: log or modify behavior for authenticated users.
  }

}

Register in services.yml

services:
  my_module.my_event_subscriber:
    class: Drupal\my_module\EventSubscriber\MyEventSubscriber
    arguments: ['@current_user']
    tags:
      - { name: event_subscriber }

Common Events

Generate with Drush

drush generate event-subscriber --answers='{
  "module": "my_module",
  "class": "MyEventSubscriber",
  "event": "kernel.request"
}'