From 352f79e9fd02e5626b8b3945ce956aa609ac765d Mon Sep 17 00:00:00 2001
From: Erik Johnston <erikj@matrix.org>
Date: Thu, 22 Sep 2016 16:24:40 +0100
Subject: [PATCH] Handle the first /sync failure differently.

A /sync request may spuriously fail on occasion, without the
"connection" actually being lost. To avoid spurious "Connection Lost"
warning messages we ignore the first /sync and immediately retry, and
only if that fails do we enter an ERROR state.
---
 lib/sync.js | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/lib/sync.js b/lib/sync.js
index f1581cd32..dea2feb28 100644
--- a/lib/sync.js
+++ b/lib/sync.js
@@ -545,13 +545,22 @@ SyncApi.prototype._sync = function(syncOptions) {
         console.error("/sync error %s", err);
         console.error(err);
 
-        debuglog("Starting keep-alive");
-        self._syncConnectionLost = true;
-        self._startKeepAlives().done(function() {
+        if (!self._syncConnectionLost) {
+            // This is the first failure, which may be spurious. To avoid unnecessary
+            // connection error warnings we simply retry the /sync immediately. Only
+            // if *that* one fails too do we say the connection has been lost.
+            // Should we emit a state like "MAYBE_CONNETION_LOST"?
+            self._syncConnectionLost = true;
             self._sync(syncOptions);
-        });
-        self._currentSyncRequest = null;
-        self._updateSyncState("ERROR", { error: err });
+        } else {
+            debuglog("Starting keep-alive");
+            self._syncConnectionLost = true;
+            self._startKeepAlives().done(function() {
+                self._sync(syncOptions);
+            });
+            self._currentSyncRequest = null;
+            self._updateSyncState("ERROR", { error: err });
+        }
     });
 };