docs: def _ReceiveOp(self):
      """Receives a single message through Fleetspeak."""
      try:
        fs_msg, received_bytes = self._fs.Recv()
      except (IOError, struct.error):
        logging.critical("Broken local Fleetspeak connection (read end).")
        raise
  
      received_type = fs_msg.data.TypeName()
      if not received_type.endswith("grr.GrrMessage"):
        raise ValueError(
            "Unexpected proto type received through Fleetspeak: %r; expected "
            "grr.GrrMessage." % received_type)
  
      stats_collector_instance.Get().IncrementCounter("grr_client_received_bytes",
                                                      received_bytes)
  
      grr_msg = rdf_flows.GrrMessage.FromSerializedString(fs_msg.data.value)
      # Authentication is ensured by Fleetspeak.
      grr_msg.auth_state = jobs_pb2.GrrMessage.AUTHENTICATED
  
      self._threads["Worker"].QueueMessages([grr_msg])