TestClass.php

<?php

declare (strict_types=1);
namespace Drupal\service_provider_test;

use Drupal\Core\State\StateInterface;
use Drupal\Core\DestructableInterface;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\HttpKernel\Event\ResponseEvent;
use Symfony\Component\HttpKernel\Event\RequestEvent;
use Symfony\Component\HttpKernel\KernelEvents;
class TestClass implements EventSubscriberInterface, DestructableInterface {
    
    /**
     * The state keyvalue collection.
     *
     * @var \Drupal\Core\State\StateInterface
     */
    protected $state;
    
    /**
     * Constructor.
     *
     * @param \Drupal\Core\State\StateInterface $state
     *   The state key value store.
     */
    public function __construct(StateInterface $state) {
        $this->state = $state;
    }
    
    /**
     * A simple kernel listener method.
     */
    public function onKernelRequestTest(RequestEvent $event) {
        \Drupal::messenger()->addStatus(t('The service_provider_test event subscriber fired!'));
    }
    
    /**
     * Flags the response in case a rebuild indicator is used.
     */
    public function onKernelResponseTest(ResponseEvent $event) {
        $container = \Drupal::getContainer();
        if ($container->hasParameter('container_rebuild_indicator')) {
            $event->getResponse()->headers
                ->set('container_rebuild_indicator', $container->getParameter('container_rebuild_indicator'));
        }
        if ($container->hasParameter('container_rebuild_test_parameter')) {
            $event->getResponse()->headers
                ->set('container_rebuild_test_parameter', $container->getParameter('container_rebuild_test_parameter'));
        }
    }
    
    /**
     * Registers methods as kernel listeners.
     *
     * @return array
     *   An array of event listener definitions.
     */
    public static function getSubscribedEvents() : array {
        $events[KernelEvents::REQUEST][] = [
            'onKernelRequestTest',
        ];
        $events[KernelEvents::RESPONSE][] = [
            'onKernelResponseTest',
        ];
        return $events;
    }
    
    /**
     * {@inheritdoc}
     */
    public function destruct() {
        $this->state
            ->set('service_provider_test.destructed', TRUE);
    }

}