Process incoming messages in order

This may increase processing latency a bit, particularly with large
attachments, but will ensure that messages are dispatched in the order
they are received.

It would be nice to enforce ordering on only the dispatch step, so that
we could, for example, decrypt the next websocket message while waiting
for an attachment to download, but that will require a more complicated
refactor. Will stick with the quick fix for now and revisit later.

Fixes #342

// FREEBIE

js/libtextsecure.js

@@ -39236,9 +39236,10 @@ MessageReceiver.prototype = {
         this.socket.onerror = this.onerror.bind(this);
         this.socket.onopen = this.onopen.bind(this);
         this.wsr = new WebSocketResource(this.socket, {
-            handleRequest: this.handleRequest.bind(this),
+            handleRequest: this.queueRequest.bind(this),
             keepalive: { path: '/v1/keepalive', disconnect: true }
         });
+        this.pending = Promise.resolve();
     },
     close: function() {
         this.wsr.close();
@@ -39262,10 +39263,14 @@ MessageReceiver.prototype = {
                 eventTarget.dispatchEvent(ev);
             });
     },
+    queueRequest: function(request) {
+        var handleRequest = this.handleRequest.bind(this, request);
+        this.pending = this.pending.then(handleRequest, handleRequest);
+    },
     handleRequest: function(request) {
         // TODO: handle different types of requests. for now we only expect
         // PUT /messages <encrypted IncomingPushMessageSignal>
-        textsecure.crypto.decryptWebsocketMessage(request.body, this.signalingKey).then(function(plaintext) {
+        return textsecure.crypto.decryptWebsocketMessage(request.body, this.signalingKey).then(function(plaintext) {
             var envelope = textsecure.protobuf.Envelope.decode(plaintext);
             // After this point, decoding errors are not the server's
             // fault, and we should handle them gracefully and tell the
@@ -39273,11 +39278,11 @@ MessageReceiver.prototype = {
             request.respond(200, 'OK');
 
             if (envelope.type === textsecure.protobuf.Envelope.Type.RECEIPT) {
-                this.onDeliveryReceipt(envelope);
+                return this.onDeliveryReceipt(envelope);
             } else if (envelope.content) {
-                this.handleContentMessage(envelope);
+                return this.handleContentMessage(envelope);
             } else if (envelope.legacyMessage) {
-                this.handleLegacyMessage(envelope);
+                return this.handleLegacyMessage(envelope);
             } else {
                 throw new Error('Received message with no content and no legacyMessage');
             }

libtextsecure/message_receiver.js

@@ -26,9 +26,10 @@ MessageReceiver.prototype = {
         this.socket.onerror = this.onerror.bind(this);
         this.socket.onopen = this.onopen.bind(this);
         this.wsr = new WebSocketResource(this.socket, {
-            handleRequest: this.handleRequest.bind(this),
+            handleRequest: this.queueRequest.bind(this),
             keepalive: { path: '/v1/keepalive', disconnect: true }
         });
+        this.pending = Promise.resolve();
     },
     close: function() {
         this.wsr.close();
@@ -52,10 +53,14 @@ MessageReceiver.prototype = {
                 eventTarget.dispatchEvent(ev);
             });
     },
+    queueRequest: function(request) {
+        var handleRequest = this.handleRequest.bind(this, request);
+        this.pending = this.pending.then(handleRequest, handleRequest);
+    },
     handleRequest: function(request) {
         // TODO: handle different types of requests. for now we only expect
         // PUT /messages <encrypted IncomingPushMessageSignal>
-        textsecure.crypto.decryptWebsocketMessage(request.body, this.signalingKey).then(function(plaintext) {
+        return textsecure.crypto.decryptWebsocketMessage(request.body, this.signalingKey).then(function(plaintext) {
             var envelope = textsecure.protobuf.Envelope.decode(plaintext);
             // After this point, decoding errors are not the server's
             // fault, and we should handle them gracefully and tell the
@@ -63,11 +68,11 @@ MessageReceiver.prototype = {
             request.respond(200, 'OK');
 
             if (envelope.type === textsecure.protobuf.Envelope.Type.RECEIPT) {
-                this.onDeliveryReceipt(envelope);
+                return this.onDeliveryReceipt(envelope);
             } else if (envelope.content) {
-                this.handleContentMessage(envelope);
+                return this.handleContentMessage(envelope);
             } else if (envelope.legacyMessage) {
-                this.handleLegacyMessage(envelope);
+                return this.handleLegacyMessage(envelope);
             } else {
                 throw new Error('Received message with no content and no legacyMessage');
             }