HtmlResponseSubscriber.php

<?php

namespace Drupal\Core\EventSubscriber;

use Drupal\Core\Render\HtmlResponse;
use Drupal\Core\Render\AttachmentsResponseProcessorInterface;
use Symfony\Component\HttpKernel\Event\ResponseEvent;
use Symfony\Component\HttpKernel\KernelEvents;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;

/**
 * Response subscriber to handle HTML responses.
 */
class HtmlResponseSubscriber implements EventSubscriberInterface {
    
    /**
     * The HTML response attachments processor service.
     *
     * @var \Drupal\Core\Render\AttachmentsResponseProcessorInterface
     */
    protected $htmlResponseAttachmentsProcessor;
    
    /**
     * Constructs a HtmlResponseSubscriber object.
     *
     * @param \Drupal\Core\Render\AttachmentsResponseProcessorInterface $html_response_attachments_processor
     *   The HTML response attachments processor service.
     */
    public function __construct(AttachmentsResponseProcessorInterface $html_response_attachments_processor) {
        $this->htmlResponseAttachmentsProcessor = $html_response_attachments_processor;
    }
    
    /**
     * Processes attachments for HtmlResponse responses.
     *
     * @param \Symfony\Component\HttpKernel\Event\ResponseEvent $event
     *   The event to process.
     */
    public function onRespond(ResponseEvent $event) {
        $response = $event->getResponse();
        if (!$response instanceof HtmlResponse) {
            return;
        }
        $event->setResponse($this->htmlResponseAttachmentsProcessor
            ->processAttachments($response));
    }
    
    /**
     * {@inheritdoc}
     */
    public static function getSubscribedEvents() : array {
        $events[KernelEvents::RESPONSE][] = [
            'onRespond',
        ];
        return $events;
    }

}