Attempts to increase the chances of unavailable presence reaching Prosody (on window unload, for example).

modules/xmpp/ChatRoom.js

     logger.log("do leave", this.myroomjid);
     var pres = $pres({to: this.myroomjid, type: 'unavailable' });
     this.presMap.length = 0;
+
+    // XXX Strophe is asynchronously sending by default. Unfortunately, that
+    // means that there may not be enough time to send the unavailable presence.
+    // Switching Strophe to synchronous sending is not much of an option because
+    // it may lead to a noticeable delay in navigating away from the current
+    // location. As a compromise, we will try to increase the chances of sending
+    // the unavailable presence within the short time span that we have upon
+    // unloading by invoking flush() on the connection. We flush() once before
+    // sending/queuing the unavailable presence in order to attemtp to have the
+    // unavailable presence at the top of the send queue. We flush() once more
+    // after sending/queuing the unavailable presence in order to attempt to
+    // have it sent as soon as possible.
+    this.connection.flush();
     this.connection.send(pres);
+    this.connection.flush();
 };
 
 

modules/xmpp/xmpp.js

 };
 
 XMPP.prototype.disconnect = function () {
-    if (this.disconnectInProgress || !this.connection || !this.connection.connected)
-    {
+    if (this.disconnectInProgress
+            || !this.connection
+            || !this.connection.connected) {
         this.eventEmitter.emit(JitsiConnectionEvents.WRONG_STATE);
         return;
     }
 
     this.disconnectInProgress = true;
 
+    // XXX Strophe is asynchronously sending by default. Unfortunately, that
+    // means that there may not be enough time to send an unavailable presence
+    // or disconnect at all. Switching Strophe to synchronous sending is not
+    // much of an option because it may lead to a noticeable delay in navigating
+    // away from the current location. As a compromise, we will try to increase
+    // the chances of sending an unavailable presence and/or disconecting within
+    // the short time span that we have upon unloading by invoking flush() on
+    // the connection. We flush() once before disconnect() in order to attemtp
+    // to have its unavailable presence at the top of the send queue. We flush()
+    // once more after disconnect() in order to attempt to have its unavailable
+    // presence sent as soon as possible.
+    this.connection.flush();
     this.connection.disconnect();
+    this.connection.flush();
 };
 
 module.exports = XMPP;