code: def detach(self) -> iostream.IOStream:
          
          self._clear_callbacks()
          stream = self.stream
          self.stream = None  # type: ignore
          if not self._finish_future.done():
              future_set_result_unless_cancelled(self._finish_future, None)
          return stream
docs: Take control of the underlying stream.
  
          Returns the underlying `.IOStream` object and stops all further
          HTTP processing.  May only be called during
          `.HTTPMessageDelegate.headers_received`.  Intended for implementing
          protocols like websockets that tunnel over an HTTP handshake.