gistfile1.txt

<?php

namespace Drupal\yourmodule\EventSubscriber;

use Drupal\Core\Cache\CacheableResponseInterface;
use Drupal\Core\Config\ConfigFactoryInterface;
use Drupal\Core\Path\CurrentPathStack;
use Drupal\Core\Session\AccountInterface;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\HttpKernel\Event\FilterResponseEvent;
use Symfony\Component\HttpKernel\KernelEvents;

/**
 * Ensures that certain pages are cached correctly for anonymous users.
 */
class CacheResponseSubscriber implements EventSubscriberInterface {

  /**
   * The current user.
   *
   * @var \Drupal\Core\Session\AccountInterface
   */
  protected $user;

  /**
   * Config factory service.
   *
   * @var \Drupal\Core\Config\ConfigFactoryInterface
   */
  protected $configFactory;

  /**
   * The current path.
   *
   * @var \Drupal\Core\Path\CurrentPathStack
   */
  protected $currentPath;

  /**
   * CacheResponseSubscriber constructor.
   *
   * @param \Drupal\Core\Session\AccountInterface $user
   *   Current user.
   * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
   *   The config factory service.
   * @param \Drupal\Core\Path\CurrentPathStack $current_path
   *   The current path.
   */
  public function __construct(AccountInterface $user, ConfigFactoryInterface $config_factory, CurrentPathStack $current_path) {
    $this->user = $user;
    $this->configFactory = $config_factory;
    $this->currentPath = $current_path;
  }

  /**
   * Updates response cache metadata.
   *
   * @param \Symfony\Component\HttpKernel\Event\FilterResponseEvent $event
   *   The kernel response event.
   */
  public function onKernelResponse(FilterResponseEvent $event) {
    $response = $event->getResponse();
    // Do nothing if a response does not have cacheable metadata.
    if (!$response instanceof CacheableResponseInterface) {
      return;
    }

    if (!$this->user->isAnonymous()) {
      return;
    }

    $cache_max_age = $response->getCacheableMetadata()->getCacheMaxAge();

    // Allow some specific paths override max-age through config.
    $pages = $this->configFactory->get('yourmodule_settings.settings')->get('anonymous_cached_pages');
    $current_path = $this->currentPath->getPath();
    $path_info = $event->getRequest()->getPathInfo();
    if (isset($pages[$current_path])) {
      $response->setExpires(new \DateTime($pages[$current_path] . 'sec'));
    }
    if (isset($pages[$path_info])) {
      $response->setExpires(new \DateTime($pages[$path_info] . 'sec'));
    }
    elseif ($cache_max_age > 0) {
      $response->setExpires(new \DateTime($cache_max_age . 'sec'));
    }
  }

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

}