I'm currently working on a Project in my University which is an Android-App which is supposed to deliver data to a Server.

In order to do that I require a more or less consistent connection to the server via XMPP. It is not really important that the connection is there 100% of the time, but it because the system is supposed to be more or less invisible to the user, user-interaction is supposed to be minimal.

Both the server and the client are xmpp-clients. I use 开发者_JAVA技巧jabber.org as the xmpp server.

I have an Android-Service that is establishing the connection to server and delivers data and this works fine.

Now I tried to make the Service reconnect when connection is lost or is Changed from Wifi to GSM. I wanted to try to make this work with a broadcastreceiver listening to NETWORK_STATE_CHANGED_ACTION. But I did not even get this far.

This is the problem: I tried running the app and then just disabling my wifi. My Phone than automatically switches to GSM and I lose my connection (which I anticipated). But when I try to reconnect manually (e.g. restarting the service) I get errors from the Server. Also my status is still "available". From that moment on it takes way too long until I can connect again.

06-29 18:12:14.888: WARN/System.err(14246): resource-constraint(500)
06-29 18:12:14.890: WARN/System.err(14246):     at org.jivesoftware.smack.NonSASLAuthentication.authenticate(NonSASLAuthentication.java:110)
06-29 18:12:14.890: WARN/System.err(14246):     at org.jivesoftware.smack.XMPPConnection.login(XMPPConnection.java:404)
06-29 18:12:14.890: WARN/System.err(14246):     at org.jivesoftware.smack.XMPPConnection.login(XMPPConnection.java:349)
....

I am actually connected to the xmpp Server but it does not deliver my message:

06-29 18:12:14.882: INFO/System.out(14246): 06:12:14 nachm. RCV  (1079704816): <iq type='error' id='7rhk4-70'><error code='500' type='wait'><resource-constraint xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/></error></iq>

Sometimes I don't get the error, but still no messages are being delivered.

So I think that the server is not allowing me to connect, because I did not disconnect before trying to reconnect. Which I find strange because I thought you could even connect from multiple clients to one account.

I'm posting some code that I think might be relevant:

public void connectToServer() throws XMPPException {

    ConnectionConfiguration config = new ConnectionConfiguration(
            serverADD, port,
            service);

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

    SASLAuthentication.supportSASLMechanism("PLAIN", 0);

    connection.login(user_JID,password);

    Presence presence = new Presence(Presence.Type.available);
            presence.setStatus("available");
            presence.setPriority(24);
    presence.setMode(Presence.Mode.available);
        connection.sendPacket(presence);
}

this is how I send the messages:

public void sendMessage(String message, String recipient) throws XMPPException {

    chat = connection.getChatManager().createChat(recipient, this);
    chat.sendMessage(message);

}

Does anyone hava an idea how to solve this? I would even use "dirty" tricks as long as my message gets delivered to the server.

By the way: The senders and the recipients jids are always the same (after initial setup). Just in case anyone thinks that could matter.

Deadlock during Smack disconnect

As Airsource Ltd. mentioned in his comment: Smack is suffering from an deadlock in disconnect() which is loged as SMACK-278. I have made a commit that fixes this in my smack fork.

Android reconnection handling

For the network fallover, have a look at the GTalkSMS receiver. It will issue a ACTION_NETWORK_CHANGED intent, with the boolean extras "available" and "fallover". Your service should "stop" the connection when "available=false" and "fallover=false". How you "stop" the connection is up to you. Sometimes the disconnect() takes very long even with the fix for SMACK-278, this is why we do the disconnect in an thread that will abort after x seconds and then creates a new Connection instance. We reconnect then when the intent with "available=true" is received.

You will find other examples in the GTalkSMS source. I have the app permanently running and it achieves a stable, but not 100% available connection (because of WLAN <-> GSM switches).