docs: def validate_response(self, resp):
          """
          Validates resp against expected return type for this function.  
          Raises RpcException if the response is invalid.
          """
          ok, msg = self.contract.validate(self.returns, 
                                           self.returns.is_array, resp)
          if not ok:
              vals = (self.full_name, str(resp), msg)
              msg = "Function '%s' invalid response: '%s'. %s" % vals
              raise RpcException(ERR_INVALID_RESP, msg)