Smack 4.1.0 GCM CCS stops responding after a while

Question

Have implemented gcm ccs for chat module and i am able to send and receive messages. Below is the main connection module,

        config = XMPPTCPConnectionConfiguration.builder()
                .setServiceName("gcm-pesu.googleapis.com")
                .setPort(GCM_PORT)
                .setHost(GCM_SERVER)
                .setCompressionEnabled(false)
                .setConnectTimeout(30000)
                .setSecurityMode(SecurityMode.ifpossible)
                .setSendPresence(false)
                .setSocketFactory(SSLSocketFactory.getDefault())
                .build();

        connection = new XMPPTCPConnection(config);
        connection.connect();

        Roster roster = Roster.getInstanceFor(connection);
        roster.setRosterLoadedAtLogin(false);

        connection.addConnectionListener(new LoggingConnectionListener());

        // Handle incoming packets
        connection.addAsyncStanzaListener(new MyStanzaListener(), new MyStanzaFilter());

        // Log all outgoing packets
        connection.addPacketInterceptor(new MyStanzaInterceptor(), new MyStanzaFilter());

        connection.login(mProjectId + "@gcm.googleapis.com", mApiKey);
        logger.info("logged in: " + mProjectId);

        PingManager pm = PingManager.getInstanceFor(connection);
        pm.setPingInterval(300);
        pm.pingMyServer();
        pm.registerPingFailedListener(new PingFailedListener() {
            @Override
            public void pingFailed() {
                connection.disconnect();
                logger.error("GCM CCS, Ping failed !!");
            }
        });

The problem i am running into is not receiving any message from GCM, sent by client device after a while. Though, the heartbeat looks normal and i do get pong from GCM even in that case. Is it something to do with SSL ?

Have handled connection draining case as follows,

        String controlType = (String) jsonObject.get("control_type");
        volatile boolean connectionDraining = false;
        if ("CONNECTION_DRAINING".equals(controlType)) {
            connectionDraining = true;
            try {
                connection.disconnect();
                connect();
                connectionDraining = false;
            } catch (Exception e) {
                logger.error("Error establishing new connection after draining ", e);
            }
        }

Answer 1

Implemented queue of channels when one of it is draining.

            private Deque<Channel> channels;
            protected void handleControlMessage(Map<String, Object> jsonObject) {
            logger.info("Control message : " + jsonObject);
            String controlType = (String) jsonObject.get("control_type");
            if ("CONNECTION_DRAINING".equals(controlType)) {
                connectionDraining = true;
            } 
        }

Create new channel while sending message

        public void sendDownstreamMessage(String jsonRequest) {
        Channel channel = channels.peekFirst();
        try {
            if (channel.connectionDraining) {
                synchronized (channels) {
                    channel = channels.peekFirst();
                    if (channel.connectionDraining) {
                        channels.addFirst(connect());
                        channel = channels.peekFirst();
                    }
                }
            }
            channel.send(jsonRequest);
        } catch (Exception e) {
            logger.error("Message not sent. Error in connecting :", e);
        }
    }

GCM will take care of closing the other. This resolved the issue.

Answer 2

I believe you're facing a common case using gcm css that is not very visible in the documentation. If you look in the doc, Control Messages you'll read:

Periodically, CCS needs to close down a connection to perform load balancing. Before it closes the connection, CCS sends a CONNECTION_DRAINING message to indicate that the connection is being drained and will be closed soon. "Draining" refers to shutting off the flow of messages coming into a connection, but allowing whatever is already in the pipeline to continue. When you receive a CONNECTION_DRAINING message, you should immediately begin sending messages to another CCS connection, opening a new connection if necessary. You should, however, keep the original connection open and continue receiving messages that may come over the connection (and ACKing them)—CCS handles initiating a connection close when it is ready.