XMPP server in java does not receive all messages from GCM server

Question

I've implemented XMPP server using Smack library, my server gets messages from Google Cloud Messaging server (now it is Firebase), but the problem is when I send one by one message from android to gcm server, my XMPP server receives only first message and the second is intercepted, (I can see only notification that there was a message

<message id="gQaM0-6"><gcm xmlns="google:mobile:data">{"message_type":"ack","message_id":"0","to":"eVtypIWW7Q8:APA91bH5oU0AC3zyuCAWVYkMzoGQeIiGe71c2BL4lE5uFHRfB3iPXtD-qIJDmJZ3ySsPDi0VhkKl0Cz3XZG7rWa1Ca7pX9yQqzWSMXBiGK4SEO4Q-Owfr45E_VBJMrXqsSziuJhek"}</gcm></message>

but I don't have data in this and first message I get in method void processPacket(Packet packet) here is the full code of XMPP server:

public class XMPPServer implements PacketListener {

    private static XMPPServer sInstance = null;
    private XMPPConnection connection;
    private ConnectionConfiguration config;
    private String mApiKey = null;
    private String mProjectId = null;
    private boolean mDebuggable = false;
    private String fcmServerUsername = null;

    public static XMPPServer getInstance() {
        if (sInstance == null) {
            throw new IllegalStateException("You have to prepare the client first");
        }
        return sInstance;
    }

    public static XMPPServer prepareClient(String projectId, String apiKey, boolean debuggable) {
        synchronized (XMPPServer.class) {
            if (sInstance == null) {
                sInstance = new XMPPServer(projectId, apiKey, debuggable);
            }
        }
        return sInstance;
    }

    private XMPPServer(String projectId, String apiKey, boolean debuggable) {
        this();
        mApiKey = apiKey;
        mProjectId = projectId;
        mDebuggable = debuggable;
        fcmServerUsername = mProjectId + "@" + Util.FCM_SERVER_CONNECTION;
    }

    private XMPPServer() {
        // Add GcmPacketExtension
        ProviderManager.getInstance().addExtensionProvider(Util.FCM_ELEMENT_NAME, Util.FCM_NAMESPACE,
                new PacketExtensionProvider() {

                    @Override
                    public PacketExtension parseExtension(XmlPullParser parser) throws Exception {
                        String json = parser.nextText();
                        GcmPacketExtension packet = new GcmPacketExtension(json);
                        return packet;
                    }
                });
    }

    /**
     * Connects to FCM Cloud Connection Server using the supplied credentials
     */
    public void connect() throws XMPPException {
        config = new ConnectionConfiguration(Util.FCM_SERVER, Util.FCM_PORT);
        config.setSecurityMode(SecurityMode.enabled);
        config.setReconnectionAllowed(true);
        config.setSocketFactory(SSLSocketFactory.getDefault());
        // Launch a window with info about packets sent and received
        config.setDebuggerEnabled(mDebuggable);

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

        connection.addConnectionListener(new ConnectionListener() {
                //a few overrided methods
        });
        // Handle incoming packets (the class implements the PacketListener)
        connection.addPacketListener(this, new PacketTypeFilter(Message.class));

        // Second message without data I get in this method (1)
        connection.addPacketWriterInterceptor(new PacketInterceptor() {
            @Override
            public void interceptPacket(Packet packet) {
                System.out.println("INTERCEPT PACKAGE: " + packet.toXML());
            }
        }, new PacketTypeFilter(Message.class));
        connection.login(fcmServerUsername, mApiKey);
    }
    /**
     * Normal message with my data I get in this method (2)
     */
    @SuppressWarnings("unchecked")
    @Override
    public void processPacket(Packet packet) {
        Message incomingMessage = (Message) packet;
        GcmPacketExtension gcmPacket = (GcmPacketExtension) incomingMessage.getExtension(Util.FCM_NAMESPACE);
        String json = gcmPacket.getJson();
        System.out.println("Message : " + json);
     }

There is almost the whole code, the most important part I marked with (1) and (2), (use search to find quickly) Why can I receive only first message with my data ? And why does the second message go to PacketInterceptor (mark (1) ) ?

score 0 · Accepted Answer · edited May 23 '17 at 10:31

If you're using Firebase Cloud Messaging(FCM), check if your app server is connected to the following endpoints:

// Production
fcm-xmpp.googleapis.com:5235

// Testing
fcm-xmpp.googleapis.com:5236

In addition to that, you may want to also check Downstream messages wherein it was mentioned that once the XMPP connection is established, CCS and your server use normal XMPP <message> stanzas to send JSON-encoded messages back and forth. The body of the <message> must be:

<gcm xmlns:google:mobile:data>
    JSON payload
</gcm>

Also, note of the exceptions in JSON payload for regular FCM messages. Visit the given links for more information.

These related SO posts might also help:

hey, thanks for your answer! I use FCM_PORT = 5236, I will try 5235, maybe this will change situation — Dmitry, Apr 17 '17 at 18:35

XMPP server in java does not receive all messages from GCM server

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