code: func (g *memberSet) NotifyMsg(b []byte) {
  	err := g.papi.ClusterMessage(context.Background(), bytes.NewBuffer(b))
  	if err != nil {
  		g.Logger.Printf("cluster message error: %s", err)
  	}
  }
docs: // NotifyMsg implementation of the memberlist.Delegate interface
  // called when a user-data message is received.