From 0cb04005dbf14724309c052cbf8f7e226498dac9 Mon Sep 17 00:00:00 2001
From: Kegan Dougal <kegan@matrix.org>
Date: Wed, 18 May 2022 19:22:54 +0100
Subject: [PATCH] Actually return a response with timeout=0

---
 syncapi/sync/requestpool.go | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/syncapi/sync/requestpool.go b/syncapi/sync/requestpool.go
index 4908700dd..7b9526b53 100644
--- a/syncapi/sync/requestpool.go
+++ b/syncapi/sync/requestpool.go
@@ -381,11 +381,14 @@ func (rp *RequestPool) OnIncomingSyncRequest(req *http.Request, device *userapi.
 			//   they weren't always doing, resulting in flakey tests.
 			if !syncReq.Response.HasUpdates() {
 				syncReq.Since = currentPos
-				syncReq.Timeout = syncReq.Timeout - time.Since(startTime)
-				if syncReq.Timeout < 0 {
-					syncReq.Timeout = 0
+				// do not loop again if the ?timeout= is 0 as that means "return immediately"
+				if syncReq.Timeout > 0 {
+					syncReq.Timeout = syncReq.Timeout - time.Since(startTime)
+					if syncReq.Timeout < 0 {
+						syncReq.Timeout = 0
+					}
+					continue
 				}
-				continue
 			}
 		}