code: func (m *mux) Disconnect(reason uint32, message string) error {
  	return m.sendMessage(disconnectMsg{
  		Reason:  reason,
  		Message: message,
  	})
  }
docs: // TODO(hanwen): Disconnect is a transport layer message. We should
  // probably send and receive Disconnect somewhere in the transport
  // code.
  // Disconnect sends a disconnect message.