code: def set_body_s(self, stream):
          
          if self.argstreams[2].state == StreamState.init:
              self.argstreams[2] = stream
          else:
              raise TChannelError(
                  "Unable to change the body since the streaming has started")
docs: Set customized body stream.
  
          Note: the body stream can only be changed before the stream
          is consumed.
  
          :param stream: InMemStream/PipeStream for body
  
          :except TChannelError:
              Raise TChannelError if the stream is being sent when you try
              to change the stream.