code: func (m *Driver) On(n string, f func(msg interface{})) error {
  	// TODO: also be able to subscribe to Error updates
  	f1 := func(msg Message) {
  		f(msg)
  	}
  	m.adaptor().On(m.topic, f1)
  	return nil
  }
docs: // On subscribes to data updates for the current device topic,
  // and then calls the message handler function when data is received