code: func (s *StanServer) ackPublisher(iopm *ioPendingMsg) {
  	msgAck := &iopm.pa
  	msgAck.Guid = iopm.pm.Guid
  	needed := msgAck.Size()
  	s.tmpBuf = util.EnsureBufBigEnough(s.tmpBuf, needed)
  	n, _ := msgAck.MarshalTo(s.tmpBuf)
  	if s.trace {
  		pm := &iopm.pm
  		s.log.Tracef("[Client:%s] Acking Publisher subj=%s guid=%s", pm.ClientID, pm.Subject, pm.Guid)
  	}
  	s.ncs.Publish(iopm.m.Reply, s.tmpBuf[:n])
  }
docs: // ackPublisher sends the ack for a message.