From c43d8981191ea993d78dea8be93fe513ad107c3e Mon Sep 17 00:00:00 2001
From: Kegan Dougal <kegan@matrix.org>
Date: Mon, 12 Jan 2015 17:38:30 +0000
Subject: [PATCH] SYN-178: Fix off by one.

---
 synapse/storage/stream.py | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/synapse/storage/stream.py b/synapse/storage/stream.py
index bedc3c6c5..744c821df 100644
--- a/synapse/storage/stream.py
+++ b/synapse/storage/stream.py
@@ -284,8 +284,12 @@ class StreamStore(SQLBaseStore):
             rows.reverse()  # As we selected with reverse ordering
 
             if rows:
-                topo = rows[0]["topological_ordering"]
-                toke = rows[0]["stream_ordering"]
+                # XXX: Always subtract 1 since the start token always goes
+                # backwards (parity with paginate_room_events). It isn't
+                # obvious that this is correct; we should clarify the algorithm
+                # used here.
+                topo = rows[0]["topological_ordering"] - 1
+                toke = rows[0]["stream_ordering"] - 1
                 start_token = "t%s-%s" % (topo, toke)
 
                 token = (start_token, end_token)