class DynamicPageCacheSubscriber in Zircon Profile 8

Returns cached responses as early and avoiding as much work as possible.

Dynamic Page Cache is able to cache so much because it utilizes cache contexts: the cache contexts that are present capture the variations of every component of the page. That, combined with the fact that cacheability metadata is bubbled, means that the cache contexts at the page level represent the complete set of contexts that the page varies by.

The reason Dynamic Page Cache is implemented as two event subscribers (a late REQUEST subscriber immediately after routing for cache hits, and an early RESPONSE subscriber for cache misses) is because many cache contexts can only be evaluated after routing. (Examples: 'user', 'user.permissions', 'route' …) Consequently, it is impossible to implement Dynamic Page Cache as a kernel middleware that simply caches per URL.

Hierarchy

• class \Drupal\dynamic_page_cache\EventSubscriber\DynamicPageCacheSubscriber implements EventSubscriberInterface

See also

\Drupal\Core\Render\MainContent\HtmlRenderer

\Drupal\Core\Cache\CacheableResponseInterface

2 files declare their use of DynamicPageCacheSubscriber

DynamicPageCacheIntegrationTest.php in core/modules/dynamic_page_cache/src/Tests/DynamicPageCacheIntegrationTest.php

Contains \Drupal\dynamic_page_cache\Tests\DynamicPageCacheIntegrationTest.

StandardTest.php in core/profiles/standard/src/Tests/StandardTest.php

Contains \Drupal\standard\Tests\StandardTest.

1 string reference to 'DynamicPageCacheSubscriber'

dynamic_page_cache.services.yml in core/modules/dynamic_page_cache/dynamic_page_cache.services.yml

core/modules/dynamic_page_cache/dynamic_page_cache.services.yml

1 service uses DynamicPageCacheSubscriber

dynamic_page_cache_subscriber in core/modules/dynamic_page_cache/dynamic_page_cache.services.yml

Drupal\dynamic_page_cache\EventSubscriber\DynamicPageCacheSubscriber

File

core/modules/dynamic_page_cache/src/EventSubscriber/DynamicPageCacheSubscriber.php, line 41

Contains \Drupal\dynamic_page_cache\EventSubscriber\DynamicPageCacheSubscriber.

Namespace

Drupal\dynamic_page_cache\EventSubscriber

class DynamicPageCacheSubscriber implements EventSubscriberInterface {

  /**
   * Attribute name of the Dynamic Page Cache request policy result.
   *
   * @see onRouteMatch()
   * @see onRespond()
   */
  const ATTRIBUTE_REQUEST_POLICY_RESULT = '_dynamic_page_cache_request_policy_result';

  /**
   * Name of Dynamic Page Cache's response header.
   */
  const HEADER = 'X-Drupal-Dynamic-Cache';

  /**
   * A request policy rule determining the cacheability of a response.
   *
   * @var \Drupal\Core\PageCache\RequestPolicyInterface
   */
  protected $requestPolicy;

  /**
   * A response policy rule determining the cacheability of the response.
   *
   * @var \Drupal\Core\PageCache\ResponsePolicyInterface
   */
  protected $responsePolicy;

  /**
   * The render cache.
   *
   * @var \Drupal\Core\Render\RenderCacheInterface
   */
  protected $renderCache;

  /**
   * The renderer configuration array.
   *
   * @var array
   */
  protected $rendererConfig;

  /**
   * Dynamic Page Cache's redirect render array.
   *
   * @var array
   */
  protected $dynamicPageCacheRedirectRenderArray = [
    '#cache' => [
      'keys' => [
        'response',
      ],
      'contexts' => [
        'route',
        // Some routes' controllers rely on the request format (they don't have
        // a separate route for each request format). Additionally, a controller
        // may be returning a domain object that a KernelEvents::VIEW subscriber
        // must turn into an actual response, but perhaps a format is being
        // requested that the subscriber does not support.
        // @see \Drupal\Core\EventSubscriber\AcceptNegotiation406::onViewDetect406()
        'request_format',
      ],
      'bin' => 'dynamic_page_cache',
    ],
  ];

  /**
   * Constructs a new DynamicPageCacheSubscriber object.
   *
   * @param \Drupal\Core\PageCache\RequestPolicyInterface $request_policy
   *   A policy rule determining the cacheability of a request.
   * @param \Drupal\Core\PageCache\ResponsePolicyInterface $response_policy
   *   A policy rule determining the cacheability of the response.
   * @param \Drupal\Core\Render\RenderCacheInterface $render_cache
   *   The render cache.
   * @param array $renderer_config
   *   The renderer configuration array.
   */
  public function __construct(RequestPolicyInterface $request_policy, ResponsePolicyInterface $response_policy, RenderCacheInterface $render_cache, array $renderer_config) {
    $this->requestPolicy = $request_policy;
    $this->responsePolicy = $response_policy;
    $this->renderCache = $render_cache;
    $this->rendererConfig = $renderer_config;
  }

  /**
   * Sets a response in case of a Dynamic Page Cache hit.
   *
   * @param \Symfony\Component\HttpKernel\Event\GetResponseEvent $event
   *   The event to process.
   */
  public function onRouteMatch(GetResponseEvent $event) {

    // Don't cache the response if the Dynamic Page Cache request policies are
    // not met. Store the result in a request attribute, so that onResponse()
    // does not have to redo the request policy check.
    $request = $event
      ->getRequest();
    $request_policy_result = $this->requestPolicy
      ->check($request);
    $request->attributes
      ->set(self::ATTRIBUTE_REQUEST_POLICY_RESULT, $request_policy_result);
    if ($request_policy_result === RequestPolicyInterface::DENY) {
      return;
    }

    // Sets the response for the current route, if cached.
    $cached = $this->renderCache
      ->get($this->dynamicPageCacheRedirectRenderArray);
    if ($cached) {
      $response = $this
        ->renderArrayToResponse($cached);
      $response->headers
        ->set(self::HEADER, 'HIT');
      $event
        ->setResponse($response);
    }
  }

  /**
   * Stores a response in case of a Dynamic Page Cache miss, if cacheable.
   *
   * @param \Symfony\Component\HttpKernel\Event\FilterResponseEvent $event
   *   The event to process.
   */
  public function onResponse(FilterResponseEvent $event) {
    $response = $event
      ->getResponse();

    // Dynamic Page Cache only works with cacheable responses. It does not work
    // with plain Response objects. (Dynamic Page Cache needs to be able to
    // access and modify the cacheability metadata associated with the
    // response.)
    if (!$response instanceof CacheableResponseInterface) {
      return;
    }

    // There's no work left to be done if this is a Dynamic Page Cache hit.
    if ($response->headers
      ->get(self::HEADER) === 'HIT') {
      return;
    }

    // There's no work left to be done if this is an uncacheable response.
    if (!$this
      ->shouldCacheResponse($response)) {

      // The response is uncacheable, mark it as such.
      $response->headers
        ->set(self::HEADER, 'UNCACHEABLE');
      return;
    }

    // Don't cache the response if Dynamic Page Cache's request subscriber did
    // not fire, because that means it is impossible to have a Dynamic Page
    // Cache hit. (This can happen when the master request is for example a 403
    // or 404, in which case a subrequest is performed by the router. In that
    // case, it is the subrequest's response that is cached by Dynamic Page
    // Cache, because the routing happens in a request subscriber earlier than
    // Dynamic Page Cache's and immediately sets a response, i.e. the one
    // returned by the subrequest, and thus causes Dynamic Page Cache's request
    // subscriber to not fire for the master request.)
    // @see \Drupal\Core\Routing\AccessAwareRouter::checkAccess()
    // @see \Drupal\Core\EventSubscriber\DefaultExceptionHtmlSubscriber::on403()
    $request = $event
      ->getRequest();
    if (!$request->attributes
      ->has(self::ATTRIBUTE_REQUEST_POLICY_RESULT)) {
      return;
    }

    // Don't cache the response if the Dynamic Page Cache request & response
    // policies are not met.
    // @see onRouteMatch()
    if ($request->attributes
      ->get(self::ATTRIBUTE_REQUEST_POLICY_RESULT) === RequestPolicyInterface::DENY || $this->responsePolicy
      ->check($response, $request) === ResponsePolicyInterface::DENY) {
      return;
    }

    // Embed the response object in a render array so that RenderCache is able
    // to cache it, handling cache redirection for us.
    $response_as_render_array = $this
      ->responseToRenderArray($response);
    $this->renderCache
      ->set($response_as_render_array, $this->dynamicPageCacheRedirectRenderArray);

    // The response was generated, mark the response as a cache miss. The next
    // time, it will be a cache hit.
    $response->headers
      ->set(self::HEADER, 'MISS');
  }

  /**
   * Whether the given response should be cached by Dynamic Page Cache.
   *
   * We consider any response that has cacheability metadata meeting the auto-
   * placeholdering conditions to be uncacheable. Because those conditions
   * indicate poor cacheability, and if it doesn't make sense to cache parts of
   * a page, then neither does it make sense to cache an entire page.
   *
   * But note that auto-placeholdering avoids such cacheability metadata ever
   * bubbling to the response level: while rendering, the Renderer checks every
   * subtree to see if meets the auto-placeholdering conditions. If it does, it
   * is automatically placeholdered, and consequently the cacheability metadata
   * of the placeholdered content does not bubble up to the response level.
   *
   * @param \Drupal\Core\Cache\CacheableResponseInterface
   *   The response whose cacheability to analyze.
   *
   * @return bool
   *   Whether the given response should be cached.
   *
   * @see \Drupal\Core\Render\Renderer::shouldAutomaticallyPlaceholder()
   */
  protected function shouldCacheResponse(CacheableResponseInterface $response) {
    $conditions = $this->rendererConfig['auto_placeholder_conditions'];
    $cacheability = $response
      ->getCacheableMetadata();

    // Response's max-age is at or below the configured threshold.
    if ($cacheability
      ->getCacheMaxAge() !== Cache::PERMANENT && $cacheability
      ->getCacheMaxAge() <= $conditions['max-age']) {
      return FALSE;
    }

    // Response has a high-cardinality cache context.
    if (array_intersect($cacheability
      ->getCacheContexts(), $conditions['contexts'])) {
      return FALSE;
    }

    // Response has a high-invalidation frequency cache tag.
    if (array_intersect($cacheability
      ->getCacheTags(), $conditions['tags'])) {
      return FALSE;
    }
    return TRUE;
  }

  /**
   * Embeds a Response object in a render array so that RenderCache can cache it.
   *
   * @param \Drupal\Core\Cache\CacheableResponseInterface $response
   *   A cacheable response.
   *
   * @return array
   *   A render array that embeds the given cacheable response object, with the
   *   cacheability metadata of the response object present in the #cache
   *   property of the render array.
   *
   * @see renderArrayToResponse()
   *
   * @todo Refactor/remove once https://www.drupal.org/node/2551419 lands.
   */
  protected function responseToRenderArray(CacheableResponseInterface $response) {
    $response_as_render_array = $this->dynamicPageCacheRedirectRenderArray + [
      // The data we actually care about.
      '#response' => $response,
      // Tell RenderCache to cache the #response property: the data we actually
      // care about.
      '#cache_properties' => [
        '#response',
      ],
      // These exist only to fulfill the requirements of the RenderCache, which
      // is designed to work with render arrays only. We don't care about these.
      '#markup' => '',
      '#attached' => '',
    ];

    // Merge the response's cacheability metadata, so that RenderCache can take
    // care of cache redirects for us.
    CacheableMetadata::createFromObject($response
      ->getCacheableMetadata())
      ->merge(CacheableMetadata::createFromRenderArray($response_as_render_array))
      ->applyTo($response_as_render_array);
    return $response_as_render_array;
  }

  /**
   * Gets the embedded Response object in a render array.
   *
   * @param array $render_array
   *   A render array with a #response property.
   *
   * @return \Drupal\Core\Cache\CacheableResponseInterface
   *   The cacheable response object.
   *
   * @see responseToRenderArray()
   */
  protected function renderArrayToResponse(array $render_array) {
    return $render_array['#response'];
  }

  /**
   * {@inheritdoc}
   */
  public static function getSubscribedEvents() {
    $events = [];

    // Run after AuthenticationSubscriber (necessary for the 'user' cache
    // context; priority 300) and MaintenanceModeSubscriber (Dynamic Page Cache
    // should not be polluted by maintenance mode-specific behavior; priority
    // 30), but before ContentControllerSubscriber (updates _controller, but
    // that is a no-op when Dynamic Page Cache runs; priority 25).
    $events[KernelEvents::REQUEST][] = [
      'onRouteMatch',
      27,
    ];

    // Run before HtmlResponseSubscriber::onRespond(), which has priority 0.
    $events[KernelEvents::RESPONSE][] = [
      'onResponse',
      100,
    ];
    return $events;
  }

}

Members

Name	Modifiers	Type	Description	Overrides
DynamicPageCacheSubscriber::$dynamicPageCacheRedirectRenderArray	protected	property	Dynamic Page Cache's redirect render array.
DynamicPageCacheSubscriber::$renderCache	protected	property	The render cache.
DynamicPageCacheSubscriber::$rendererConfig	protected	property	The renderer configuration array.
DynamicPageCacheSubscriber::$requestPolicy	protected	property	A request policy rule determining the cacheability of a response.
DynamicPageCacheSubscriber::$responsePolicy	protected	property	A response policy rule determining the cacheability of the response.
DynamicPageCacheSubscriber::ATTRIBUTE_REQUEST_POLICY_RESULT		constant	Attribute name of the Dynamic Page Cache request policy result.
DynamicPageCacheSubscriber::getSubscribedEvents	public static	function	Returns an array of event names this subscriber wants to listen to. Overrides EventSubscriberInterface::getSubscribedEvents
DynamicPageCacheSubscriber::HEADER		constant	Name of Dynamic Page Cache's response header.
DynamicPageCacheSubscriber::onResponse	public	function	Stores a response in case of a Dynamic Page Cache miss, if cacheable.
DynamicPageCacheSubscriber::onRouteMatch	public	function	Sets a response in case of a Dynamic Page Cache hit.
DynamicPageCacheSubscriber::renderArrayToResponse	protected	function	Gets the embedded Response object in a render array.
DynamicPageCacheSubscriber::responseToRenderArray	protected	function	Embeds a Response object in a render array so that RenderCache can cache it.
DynamicPageCacheSubscriber::shouldCacheResponse	protected	function	Whether the given response should be cached by Dynamic Page Cache.
DynamicPageCacheSubscriber::__construct	public	function	Constructs a new DynamicPageCacheSubscriber object.