Always update AS last_pos, even on no events (#10107)

Fixes #1834.

`get_new_events_for_appservice` internally calls `get_events_as_list`, which will filter out any rejected events. If all returned events are filtered out, `_notify_interested_services` will return without updating the last handled stream position. If there are 100 consecutive such events, processing will halt altogether.

Breaking the loop is now done by checking whether we're up-to-date with `current_max` in the loop condition, instead of relying on an empty `events` list.


Signed-off-by: Willem Mulder <14mRh4X0r@gmail.com>

changelog.d/10107.bugfix

@@ -0,0 +1 @@
+Fixed a bug that could cause Synapse to stop notifying application services. Contributed by Willem Mulder.

synapse/handlers/appservice.py

@@ -87,17 +87,15 @@ async def _notify_interested_services(self, max_token: RoomStreamToken):
             self.is_processing = True
             try:
                 limit = 100
-                while True:
+                upper_bound = -1
+                while upper_bound < self.current_max:
                     (
                         upper_bound,
                         events,
                     ) = await self.store.get_new_events_for_appservice(
                         self.current_max, limit
                     )
 
-                    if not events:
-                        break
-
                     events_by_room = {}  # type: Dict[str, List[EventBase]]
                     for event in events:
                         events_by_room.setdefault(event.room_id, []).append(event)
@@ -153,9 +151,6 @@ async def handle_room_events(events):
 
                     await self.store.set_appservice_last_pos(upper_bound)
 
-                    now = self.clock.time_msec()
-                    ts = await self.store.get_received_ts(events[-1].event_id)
-
                     synapse.metrics.event_processing_positions.labels(
                         "appservice_sender"
                     ).set(upper_bound)
@@ -168,12 +163,16 @@ async def handle_room_events(events):
 
                     event_processing_loop_counter.labels("appservice_sender").inc()
 
-                    synapse.metrics.event_processing_lag.labels(
-                        "appservice_sender"
-                    ).set(now - ts)
-                    synapse.metrics.event_processing_last_ts.labels(
-                        "appservice_sender"
-                    ).set(ts)
+                    if events:
+                        now = self.clock.time_msec()
+                        ts = await self.store.get_received_ts(events[-1].event_id)
+
+                        synapse.metrics.event_processing_lag.labels(
+                            "appservice_sender"
+                        ).set(now - ts)
+                        synapse.metrics.event_processing_last_ts.labels(
+                            "appservice_sender"
+                        ).set(ts)
             finally:
                 self.is_processing = False
 

tests/handlers/test_appservice.py

@@ -57,10 +57,10 @@ def test_notify_interested_services(self):
             sender="@someone:anywhere", type="m.room.message", room_id="!foo:bar"
         )
         self.mock_store.get_new_events_for_appservice.side_effect = [
-            make_awaitable((0, [event])),
             make_awaitable((0, [])),
+            make_awaitable((1, [event])),
         ]
-        self.handler.notify_interested_services(RoomStreamToken(None, 0))
+        self.handler.notify_interested_services(RoomStreamToken(None, 1))
 
         self.mock_scheduler.submit_event_for_as.assert_called_once_with(
             interested_service, event
@@ -77,7 +77,6 @@ def test_query_user_exists_unknown_user(self):
         self.mock_as_api.query_user.return_value = make_awaitable(True)
         self.mock_store.get_new_events_for_appservice.side_effect = [
             make_awaitable((0, [event])),
-            make_awaitable((0, [])),
         ]
 
         self.handler.notify_interested_services(RoomStreamToken(None, 0))
@@ -95,7 +94,6 @@ def test_query_user_exists_known_user(self):
         self.mock_as_api.query_user.return_value = make_awaitable(True)
         self.mock_store.get_new_events_for_appservice.side_effect = [
             make_awaitable((0, [event])),
-            make_awaitable((0, [])),
         ]
 
         self.handler.notify_interested_services(RoomStreamToken(None, 0))