public function onRequestError(Event $event)
    {
        $request = $event['request'];

        if (!$this->canCache->canCacheRequest($request)) {
            return;
        }

        if ($response = $this->storage->fetch($request)) {
            $response->setHeader(
                'Age',
                time() - strtotime($response->getLastModified() ? : $response->getDate() ?: 'now')
            );

            if ($this->canResponseSatisfyFailedRequest($request, $response)) {
                $request->getParams()->set('cache.hit', 'error');
                $this->addResponseHeaders($request, $response);
                $event['response'] = $response;
                $event->stopPropagation();
            }
        }
    }