SS: Reset connection if token is unrecognized (#17529)

This triggers the client to start a new sliding sync connection. If we
don't do this and the client asks for the full range of rooms, we end up
sending down all rooms and their state from scratch (which can be very
slow)

This causes things like
https://github.com/element-hq/element-x-ios/issues/3115 after we restart
the server

---------

Co-authored-by: Eric Eastwood <eric.eastwood@beta.gouv.fr>

1 files changed, 11 insertions, 17 deletions

diff --git a/tests/rest/client/sliding_sync/test_rooms_required_state.py b/tests/rest/client/sliding_sync/test_rooms_required_state.py
index 03e36914ae..a13cad223f 100644
--- a/tests/rest/client/sliding_sync/test_rooms_required_state.py
+++ b/tests/rest/client/sliding_sync/test_rooms_required_state.py
@@ -161,10 +161,10 @@ class SlidingSyncRoomsRequiredStateTestCase(SlidingSyncBase):
         self.assertIsNone(response_body["rooms"][room_id1].get("required_state"))
         self.assertIsNone(response_body["rooms"][room_id1].get("invite_state"))
 
-    def test_rooms_required_state_incremental_sync_restart(self) -> None:
+    def test_rooms_incremental_sync_restart(self) -> None:
         """
-        Test `rooms.required_state` returns requested state events in the room during an
-        incremental sync, after a restart (and so the in memory caches are reset).
+        Test that after a restart (and so the in memory caches are reset) that
+        we correctly return an `M_UNKNOWN_POS`
         """
 
         user1_id = self.register_user("user1", "pass")
@@ -195,22 +195,16 @@ class SlidingSyncRoomsRequiredStateTestCase(SlidingSyncBase):
         self.hs.get_sliding_sync_handler().connection_store._connections.clear()
 
         # Make the Sliding Sync request
-        response_body, _ = self.do_sync(sync_body, since=from_token, tok=user1_tok)
-
-        # If the cache has been cleared then we do expect the state to come down
-        state_map = self.get_success(
-            self.storage_controllers.state.get_current_state(room_id1)
+        channel = self.make_request(
+            method="POST",
+            path=self.sync_endpoint + f"?pos={from_token}",
+            content=sync_body,
+            access_token=user1_tok,
         )
-
-        self._assertRequiredStateIncludes(
-            response_body["rooms"][room_id1]["required_state"],
-            {
-                state_map[(EventTypes.Create, "")],
-                state_map[(EventTypes.RoomHistoryVisibility, "")],
-            },
-            exact=True,
+        self.assertEqual(channel.code, 400, channel.json_body)
+        self.assertEqual(
+            channel.json_body["errcode"], "M_UNKNOWN_POS", channel.json_body
         )
-        self.assertIsNone(response_body["rooms"][room_id1].get("invite_state"))
 
     def test_rooms_required_state_wildcard(self) -> None:
         """