code: func (m *mux) ackRequest(ok bool, data []byte) error {
  	if ok {
  		return m.sendMessage(globalRequestSuccessMsg{Data: data})
  	}
  	return m.sendMessage(globalRequestFailureMsg{Data: data})
  }
docs: // ackRequest must be called after processing a global request that
  // has WantReply set.