function DynamicPageCacheSubscriber::onResponse

Stores a response in case of a Dynamic Page Cache miss, if cacheable.

Parameters

\Symfony\Component\HttpKernel\Event\ResponseEvent $event: The event to process.

File

core/modules/dynamic_page_cache/src/EventSubscriber/DynamicPageCacheSubscriber.php, line 151

Class

DynamicPageCacheSubscriber

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

Namespace

Code

public function onResponse(ResponseEvent $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 = $event->getRequest();
    if (!isset($this->requestPolicyResults[$request])) {
        return;
    }
    // Don't cache the response if the Dynamic Page Cache request & response
    // policies are not met.
    // @see onRequest()
    if ($this->requestPolicyResults[$request] === 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');
}