From be9809347d2a00802d267772d42db9fb54175000 Mon Sep 17 00:00:00 2001
From: Olivier 'reivilibre <oliverw@matrix.org>
Date: Mon, 5 Jan 2026 14:03:56 +0000
Subject: [PATCH] Add a test for sticky TTL calculation and exposure to clients

---
 tests/rest/client/test_sticky_events.py | 117 ++++++++++++++++++++++++
 1 file changed, 117 insertions(+)
 create mode 100644 tests/rest/client/test_sticky_events.py

diff --git a/tests/rest/client/test_sticky_events.py b/tests/rest/client/test_sticky_events.py
new file mode 100644
index 0000000000..a16f74c425
--- /dev/null
+++ b/tests/rest/client/test_sticky_events.py
@@ -0,0 +1,117 @@
+#
+# This file is licensed under the Affero General Public License (AGPL) version 3.
+#
+# Copyright (C) 2025 New Vector, Ltd
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# See the GNU Affero General Public License for more details:
+# <https://www.gnu.org/licenses/agpl-3.0.html>.
+#
+#
+
+from twisted.internet.testing import MemoryReactor
+
+from synapse.api.constants import EventTypes, EventUnsignedContentFields
+from synapse.rest import admin
+from synapse.rest.client import login, register, room
+from synapse.server import HomeServer
+from synapse.types import JsonDict
+from synapse.util.clock import Clock
+
+from tests import unittest
+
+
+class StickyEventsClientTestCase(unittest.HomeserverTestCase):
+    """Tests sticky events retrieved via the /event/ endpoint."""
+
+    servlets = [
+        room.register_servlets,
+        login.register_servlets,
+        register.register_servlets,
+        admin.register_servlets,
+    ]
+
+    def default_config(self) -> JsonDict:
+        config = super().default_config()
+        config["experimental_features"] = {"msc4354_enabled": True}
+        return config
+
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
+        # Arrange: Register an account
+        self.user_id = self.register_user("user1", "pass")
+        self.token = self.login(self.user_id, "pass")
+
+        # Arrange: Create a room
+        self.room_id = self.helper.create_room_as(self.user_id, tok=self.token)
+
+    def _assert_event_sticky_for(self, event_id: str, sticky_ttl: int) -> None:
+        channel = self.make_request(
+            "GET",
+            f"/rooms/{self.room_id}/event/{event_id}",
+            access_token=self.token,
+        )
+
+        self.assertEqual(
+            channel.code, 200, f"could not retrieve event {event_id}: {channel.result}"
+        )
+        event = channel.json_body
+
+        self.assertIn(
+            EventUnsignedContentFields.STICKY_TTL,
+            event["unsigned"],
+            f"No {EventUnsignedContentFields.STICKY_TTL} field in {event_id}; event not sticky: {event}",
+        )
+        self.assertEqual(
+            event["unsigned"][EventUnsignedContentFields.STICKY_TTL],
+            sticky_ttl,
+            f"{event_id} had an unexpected sticky TTL: {event}",
+        )
+
+    def _assert_event_not_sticky(self, event_id: str) -> None:
+        channel = self.make_request(
+            "GET",
+            f"/rooms/{self.room_id}/event/{event_id}",
+            access_token=self.token,
+        )
+
+        self.assertEqual(
+            channel.code, 200, f"could not retrieve event {event_id}: {channel.result}"
+        )
+        event = channel.json_body
+
+        self.assertNotIn(
+            EventUnsignedContentFields.STICKY_TTL,
+            event["unsigned"],
+            f"{EventUnsignedContentFields.STICKY_TTL} field unexpectedly found in {event_id}: {event}",
+        )
+
+    def test_sticky_event_via_event_endpoint(self) -> None:
+        # Arrange: Send a sticky event with a specific duration
+        sticky_event_response = self.helper.send_sticky_event(
+            self.room_id,
+            EventTypes.Message,
+            # sticky duration is 1 minute
+            duration_ms=60_000,
+            content={"body": "sticky message", "msgtype": "m.text"},
+            tok=self.token,
+        )
+        event_id = sticky_event_response["event_id"]
+
+        # If we request the event immediately, it will still have
+        # 1 minute of stickiness
+        # The other 100 ms is advanced in FakeChannel.await_result.
+        self._assert_event_sticky_for(event_id, 59_900)
+
+        # But if we advance time by 59.799 seconds...
+        # we will get the event on its last millisecond of stickiness
+        # The other 100 ms is advanced in FakeChannel.await_result.
+        self.reactor.advance(59.799)
+        self._assert_event_sticky_for(event_id, 1)
+
+        # Advancing time any more, the event is no longer sticky
+        self.reactor.advance(0.001)
+        self._assert_event_not_sticky(event_id)