From 3d57b4ce6af0d78c733be4e3046df06eebdbb7bc Mon Sep 17 00:00:00 2001
From: Kegan Dougal <kegan@matrix.org>
Date: Wed, 9 Dec 2015 16:41:36 +0000
Subject: [PATCH] Be paranoid on /sync processing

---
 lib/sync.js | 45 +++++++++++++++++++++++++++------------------
 1 file changed, 27 insertions(+), 18 deletions(-)

diff --git a/lib/sync.js b/lib/sync.js
index 26c604b4e..77146b160 100644
--- a/lib/sync.js
+++ b/lib/sync.js
@@ -175,20 +175,30 @@ SyncApi.prototype._sync = function(syncOptions, attempt) {
         // }
         console.log("Got data %s", data);
 
-        // handle presence events (User objects)
-        if (data.presence && utils.isArray(data.presence.events)) {
-            data.presence.events.map(client.getEventMapper()).forEach(function(presenceEvent) {
-                var user = client.store.getUser(presenceEvent.getSender());
-                if (user) {
-                    user.setPresenceEvent(presenceEvent);
-                }
-                else {
-                    user = createNewUser(client, presenceEvent.getSender());
-                    user.setPresenceEvent(presenceEvent);
-                    client.store.storeUser(user);
-                }
-                client.emit("event", presenceEvent);
-            });
+        // set the sync token NOW *before* processing the events. We do this so if something
+        // barfs on an event we can skip it rather than constantly polling with the same token.
+        client.store.setSyncToken(data.next_batch);
+
+        try {
+            // handle presence events (User objects)
+            if (data.presence && utils.isArray(data.presence.events)) {
+                data.presence.events.map(client.getEventMapper()).forEach(function(presenceEvent) {
+                    var user = client.store.getUser(presenceEvent.getSender());
+                    if (user) {
+                        user.setPresenceEvent(presenceEvent);
+                    }
+                    else {
+                        user = createNewUser(client, presenceEvent.getSender());
+                        user.setPresenceEvent(presenceEvent);
+                        client.store.storeUser(user);
+                    }
+                    client.emit("event", presenceEvent);
+                });
+            }
+        }
+        catch (e) {
+            console.error("Caught /sync error:");
+            console.error(e);
         }
 
         /*
@@ -292,11 +302,10 @@ SyncApi.prototype._sync = function(syncOptions, attempt) {
             });
         }
 
+        */
+
         
-        // assume success until we fail which may be 30+ secs */
-
-        client.store.setSyncToken(data.next_batch);
-
+        // emit synced events
         if (!syncOptions.hasSyncedBefore) {
             updateSyncState(client, "PREPARED");
             syncOptions.hasSyncedBefore = true;