Fix for out-of-order message/receipt arrival

In a multi device world, it's possible to receive a receipt for a sync
message before the sync message actually arrives. In this case we need
to keep the receipt around and the process it when the message shows up.

js/background.js

@@ -102,6 +102,9 @@
             });
         }
 
+        // lazy hack
+        window.receipts = new Backbone.Collection();
+
         function onDeliveryReceipt(pushMessage) {
             var timestamp = pushMessage.timestamp.toNumber();
             var messages  = new Whisper.MessageCollection();
@@ -123,6 +126,11 @@
                             // successfully delivered to?
                         }
                     }
+                    // if we get here, we didn't find a matching message.
+                    // keep the receipt in memory in case it shows up later
+                    // as a sync message.
+                    receipts.add({ timestamp: timestamp, source: pushMessage.source });
+                    return;
                 });
             }).fail(function() {
                 console.log('got delivery receipt for unknown message', pushMessage.source, timestamp);

js/models/messages.js

@@ -130,13 +130,6 @@
             var source = message.get('source');
             var timestamp = message.get('sent_at');
             return textsecure.processDecrypted(pushMessageContent, source).then(function(pushMessageContent) {
-                var type = 'incoming';
-                if (pushMessageContent.sync) {
-                    type = 'outgoing';
-                    timestamp = pushMessageContent.sync.timestamp.toNumber();
-                }
-                var now = new Date().getTime();
-
                 var conversationId = source;
                 if (pushMessageContent.sync) {
                     conversationId = pushMessageContent.sync.destination;
@@ -144,8 +137,41 @@
                     conversationId = pushMessageContent.group.id;
                 }
                 var conversation = new Whisper.Conversation({id: conversationId});
-                var attributes = {};
                 conversation.fetch().always(function() {
+                    var type = 'incoming';
+                    if (pushMessageContent.sync) {
+                        type = 'outgoing';
+                        timestamp = pushMessageContent.sync.timestamp.toNumber();
+
+                        // lazy hack - check for receipts that arrived early.
+                        if (pushMessageContent.sync.destination) {
+                            var receipt = window.receipts.findWhere({
+                                timestamp: timestamp,
+                                source: pushMessageContent.sync.destination
+                            });
+                            if (receipt) {
+                                window.receipts.remove(receipt);
+                                message.set({
+                                    delivered: (message.get('delivered') || 0) + 1
+                                });
+                            }
+                        } else if (pushMessageContent.group.id) {  // group sync
+                            var members = conversation.get('members');
+                            var receipts = window.receipts.where({ timestamp: timestamp });
+                            for (var i in receipts) {
+                                if (members.indexOf(receipts[i].get('source')) > -1) {
+                                    window.receipts.remove(receipts[i]);
+                                    message.set({
+                                        delivered: (message.get('delivered') || 0) + 1
+                                    });
+                                }
+                            }
+                        } else {
+                            throw new Error('Received sync message with no destination and no group id');
+                        }
+                    }
+                    var now = new Date().getTime();
+                    var attributes = {};
                     if (pushMessageContent.group) {
                         var group_update = {};
                         attributes = {