code: public function processPsrRequest(
          ServerRequestInterface $request,
          ResponseInterface $response,
          StreamInterface $writableBodyStream
      ) {
          $result = $this->executePsrRequest($request);
  
          return $this->helper->toPsrResponse($result, $response, $writableBodyStream);
      }
docs: Executes PSR-7 request and fulfills PSR-7 response.
  
  See `executePsrRequest()` if you prefer to create response yourself
  (e.g. using specific JsonResponse instance of some framework).
  
  @return ResponseInterface|Promise
  
  @api