Zend\Stratigility\Http\ResponseInterface::write PHP Method

    public function write($data);

 /**
  * Ping action.
  *
  * @param ServerRequestInterface $request
  * @param ResponseInterface $response
  * @return string
  */
 public function ping(ServerRequestInterface $request, ResponseInterface $response)
 {
     $data = ['ack' => time(), 'target' => __METHOD__];
     $response->write($this->json->render($data));
     return $this->json->response($response);
 }