code: func (a *Adaptor) On(event string, f func(msg Message)) bool {
  	if a.client == nil {
  		return false
  	}
  	a.client.Subscribe(event, func(msg *nats.Msg) {
  		f(msg)
  	})
  
  	return true
  }
docs: // On is an event-handler style subscriber to a particular topic (named event).
  // Supply a handler function to use the bytes returned by the server.