Method attachClient

server.go:406–495

attachClient validates an incoming client connection and if viable, attaches the client to the server, performs session housekeeping, and reads incoming packets.

(cl *Client, listener string)

// attachClient validates an incoming client connection and if viable, attaches the client
// to the server, performs session housekeeping, and reads incoming packets.
func (s *Server) attachClient(cl *Client, listener string) error {
	defer s.Listeners.ClientsWg.Done()
	s.Listeners.ClientsWg.Add(1)

	go cl.WriteLoop()
	defer cl.Stop(nil)

	pk, err := s.readConnectionPacket(cl)
	if err != nil {
		return fmt.Errorf("read connection: %w", err)
	}

	cl.ParseConnect(listener, pk)
	if atomic.LoadInt64(&s.Info.ClientsConnected) >= s.Options.Capabilities.MaximumClients {
		if cl.Properties.ProtocolVersion < 5 {
			s.SendConnack(cl, packets.ErrServerUnavailable, false, nil)
		} else {
			s.SendConnack(cl, packets.ErrServerBusy, false, nil)
		}

		return packets.ErrServerBusy
	}

	code := s.validateConnect(cl, pk) // [MQTT-3.1.4-1] [MQTT-3.1.4-2]
	if code != packets.CodeSuccess {
		if err := s.SendConnack(cl, code, false, nil); err != nil {
			return fmt.Errorf("invalid connection send ack: %w", err)
		}
		return code // [MQTT-3.2.2-7] [MQTT-3.1.4-6]
	}

	err = s.hooks.OnConnect(cl, pk)
	if err != nil {
		return err
	}

	cl.refreshDeadline(cl.State.Keepalive)
	if !s.hooks.OnConnectAuthenticate(cl, pk) { // [MQTT-3.1.4-2]
		err := s.SendConnack(cl, packets.ErrBadUsernameOrPassword, false, nil)
		if err != nil {
			return fmt.Errorf("invalid connection send ack: %w", err)
		}

		return packets.ErrBadUsernameOrPassword
	}

	atomic.AddInt64(&s.Info.ClientsConnected, 1)
	defer atomic.AddInt64(&s.Info.ClientsConnected, -1)

	s.hooks.OnSessionEstablish(cl, pk)

	sessionPresent := s.inheritClientSession(pk, cl)
	s.Clients.Add(cl) // [MQTT-4.1.0-1]

	err = s.SendConnack(cl, code, sessionPresent, nil) // [MQTT-3.1.4-5] [MQTT-3.2.0-1] [MQTT-3.2.0-2] &[MQTT-3.14.0-1]
	if err != nil {
		return fmt.Errorf("ack connection packet: %w", err)
	}