public function onRequestBeforeSend(Event $event)
    {
        $request = $event['request'];
        $request->addHeader('Via', sprintf('%s GuzzleCache/%s', $request->getProtocolVersion(), Version::VERSION));

        if (!$this->canCache->canCacheRequest($request)) {
            switch ($request->getMethod()) {
                case 'PURGE':
                    $this->purge($request);
                    $request->setResponse(new Response(200, array(), 'purged'));
                    break;
                case 'PUT':
                case 'POST':
                case 'DELETE':
                case 'PATCH':
                    if ($this->autoPurge) {
                        $this->purge($request);
                    }
            }
            return;
        }

        if ($response = $this->storage->fetch($request)) {
            $params = $request->getParams();
            $params['cache.lookup'] = true;
            $response->setHeader(
                'Age',
                time() - strtotime($response->getDate() ? : $response->getLastModified() ?: 'now')
            );
            // Validate that the response satisfies the request
            if ($this->canResponseSatisfyRequest($request, $response)) {
                if (!isset($params['cache.hit'])) {
                    $params['cache.hit'] = true;
                }
                $request->setResponse($response);
            }
        }
    }