code: def handle_backend_response(self, orig_request, backend_request,
                                response_status, response_headers,
                                response_body, method_config, start_response):
      
      # Verify that the response is json.  If it isn't treat, the body as an
      # error message and wrap it in a json error response.
      for header, value in response_headers:
        if (header.lower() == 'content-type' and
            not value.lower().startswith('application/json')):
          return self.fail_request(orig_request,
                                   'Non-JSON reply: %s' % response_body,
                                   start_response)
  
      self.check_error_response(response_body, response_status)
  
      # Check if the response from the API was empty.  Empty REST responses
      # generate a HTTP 204.
      empty_response = self.check_empty_response(orig_request, method_config,
                                                   start_response)
      if empty_response is not None:
        return empty_response
  
      body = self.transform_rest_response(response_body)
  
      cors_handler = self._create_cors_handler(orig_request)
      return util.send_wsgi_response(response_status, response_headers, body,
                                     start_response, cors_handler=cors_handler)
docs: Handle backend response, transforming output as needed.
  
      This calls start_response and returns the response body.
  
      Args:
        orig_request: An ApiRequest, the original request from the user.
        backend_request: An ApiRequest, the transformed request that was
                         sent to the backend handler.
        response_status: A string, the status from the response.
        response_headers: A dict, the headers from the response.
        response_body: A string, the body of the response.
        method_config: A dict, the API config of the method to be called.
        start_response: A function with semantics defined in PEP-333.
  
      Returns:
        A string containing the response body.