When rebuilding the channel, subscribe via last seen ID, so we don't miss messages from the time we were disconnected.

api.py

@@ -71,10 +71,11 @@ def SendMessage(google_user, client, args):
 def Subscribe(google_user, client, args):
   subject = models.Subject.FindOrCreate(args['subject'])
   messages = args.get('messages', 0)
+  last_id = args.get('last_id', None)
   keys = args.get('keys', [])
 
   ret = {
-    'events': models.Subscription.FindOrCreate(subject, client, messages),
+    'events': models.Subscription.FindOrCreate(subject, client, messages, last_id),
   }
   for key in keys:
     message = subject.GetKey(key)

lib/models.py

@@ -117,6 +117,15 @@ class Subject(db.Model):
       num_messages = None
     return reversed(query.fetch(limit=num_messages))
 
+  @db.transactional()
+  def GetMessagesSince(self, last_id):
+    query = (
+        Message.all()
+        .ancestor(self)
+        .filter('id_ >', last_id)
+        .order('id_'))
+    return list(query)
+
   @db.transactional()
   def GetKey(self, key):
     messages = (
@@ -179,7 +188,7 @@ class Subscription(db.Model):
 
   @classmethod
   @db.transactional()
-  def FindOrCreate(cls, subject, client, messages):
+  def FindOrCreate(cls, subject, client, messages=0, last_id=None):
     subscriptions = (
         cls.all(keys_only=True)
         .ancestor(subject)
@@ -187,9 +196,12 @@ class Subscription(db.Model):
         .fetch(1))
     if not subscriptions:
       cls(parent=subject, client=client).put()
-    if messages == 0:
+    events = []
-      return []
+    if messages:
-    return [m.ToEvent() for m in subject.GetRecentMessages(messages)]
+      events.extend(m.ToEvent() for m in subject.GetRecentMessages(messages))
+    if last_id:
+      events.extend(m.ToEvent() for m in subject.GetMessagesSince(last_id))
+    return events
 
   @classmethod
   @db.transactional()

static/cosmopolite.js

@@ -423,13 +423,17 @@ Cosmopolite.prototype.createChannel_ = function() {
       'onSuccess': this.onCreateChannel_,
     },
   ];
-  // TODO(flamingcow): Need to restart from the latest message.
   for (var subject in this.subscriptions_) {
+    var subscription = this.subscriptions_[subject];
+    var last_id = 0;
+    if (subscription.messages.length > 0) {
+      last_id = subscription.messages[subscription.messages.length - 1]['id'];
+    }
     rpcs.push({
       'command': 'subscribe',
       'arguments': {
         'subject':  subject,
-        'messages': 0,
+        'last_id':  last_id,
       }
     });
   }