Google\Cloud\PubSub\Connection\Rest::__construct PHP Method

    public function __construct(array $config = [])
    {
        $emulatorHost = getenv('PUBSUB_EMULATOR_HOST');
        $baseUri = $this->getEmulatorBaseUri(self::BASE_URI, $emulatorHost);
        if ($emulatorHost) {
            $config['shouldSignRequest'] = false;
        }
        $config += ['serviceDefinitionPath' => __DIR__ . '/ServiceDefinition/pubsub-v1.json'];
        $this->setRequestWrapper(new RequestWrapper($config));
        $this->setRequestBuilder(new RequestBuilder($config['serviceDefinitionPath'], $baseUri, ['resources', 'projects']));
    }

 public function __construct()
 {
     // call parent constructor
     parent::__construct();
     // create the asyncronous curl handler
     $this->handler = new CurlMultiHandler();
     $httpClient = new Client(['handler' => HandlerStack::create($this->handler)]);
     // have the request wrapper call guzzle asyncronously
     $this->setRequestWrapper(new RequestWrapper(['scopes' => PubSubClient::FULL_CONTROL_SCOPE, 'httpHandler' => function ($request, $options = []) use($httpClient) {
         return $httpClient->sendAsync($request, $options);
     }, 'authHttpHandler' => HttpHandlerFactory::build()]));
 }