From 7da24b975dfb10c277cf963dfddb88f55b1ca598 Mon Sep 17 00:00:00 2001
From: David Baker <dbkr@users.noreply.github.com>
Date: Thu, 22 Jul 2021 15:29:27 +0100
Subject: [PATCH] Always send device_one_time_keys_count (#10457)
As per comment
Fixes https://github.com/matrix-org/synapse/issues/10456
See also https://github.com/vector-im/element-android/issues/3725
---
changelog.d/10457.bugfix | 1 +
synapse/rest/client/v2_alpha/sync.py | 11 +++++++----
2 files changed, 8 insertions(+), 4 deletions(-)
create mode 100644 changelog.d/10457.bugfix
diff --git a/changelog.d/10457.bugfix b/changelog.d/10457.bugfix
new file mode 100644
index 000000000..ec950b584
--- /dev/null
+++ b/changelog.d/10457.bugfix
@@ -0,0 +1 @@
+Always include `device_one_time_keys_count` key in `/sync` response to work around a bug in Element Android that broke encryption for new devices.
diff --git a/synapse/rest/client/v2_alpha/sync.py b/synapse/rest/client/v2_alpha/sync.py
index ecbbcf385..32e850079 100644
--- a/synapse/rest/client/v2_alpha/sync.py
+++ b/synapse/rest/client/v2_alpha/sync.py
@@ -252,10 +252,13 @@ class SyncRestServlet(RestServlet):
if sync_result.device_lists.left:
response["device_lists"]["left"] = list(sync_result.device_lists.left)
- if sync_result.device_one_time_keys_count:
- response[
- "device_one_time_keys_count"
- ] = sync_result.device_one_time_keys_count
+ # We always include this because https://github.com/vector-im/element-android/issues/3725
+ # The spec isn't terribly clear on when this can be omitted and how a client would tell
+ # the difference between "no keys present" and "nothing changed" in terms of whole field
+ # absent / individual key type entry absent
+ # Corresponding synapse issue: https://github.com/matrix-org/synapse/issues/10456
+ response["device_one_time_keys_count"] = sync_result.device_one_time_keys_count
+
if sync_result.device_unused_fallback_key_types:
response[
"org.matrix.msc2732.device_unused_fallback_key_types"