1 files changed, 21 insertions, 7 deletions
diff --git a/synapse/handlers/typing.py b/synapse/handlers/typing.py
index e22393adc4..0cb651a400 100644
--- a/synapse/handlers/typing.py
+++ b/synapse/handlers/typing.py
@@ -68,11 +68,11 @@ class FollowerTypingHandler:
             )
 
         # map room IDs to serial numbers
-        self._room_serials = {}  # type: Dict[str, int]
+        self._room_serials: Dict[str, int] = {}
         # map room IDs to sets of users currently typing
-        self._room_typing = {}  # type: Dict[str, Set[str]]
+        self._room_typing: Dict[str, Set[str]] = {}
 
-        self._member_last_federation_poke = {}  # type: Dict[RoomMember, int]
+        self._member_last_federation_poke: Dict[RoomMember, int] = {}
         self.wheel_timer = WheelTimer(bucket_size=5000)
         self._latest_room_serial = 0
 
@@ -208,6 +208,7 @@ class TypingWriterHandler(FollowerTypingHandler):
 
         self.auth = hs.get_auth()
         self.notifier = hs.get_notifier()
+        self.event_auth_handler = hs.get_event_auth_handler()
 
         self.hs = hs
 
@@ -216,7 +217,7 @@ class TypingWriterHandler(FollowerTypingHandler):
         hs.get_distributor().observe("user_left_room", self.user_left_room)
 
         # clock time we expect to stop
-        self._member_typing_until = {}  # type: Dict[RoomMember, int]
+        self._member_typing_until: Dict[RoomMember, int] = {}
 
         # caches which room_ids changed at which serials
         self._typing_stream_change_cache = StreamChangeCache(
@@ -326,6 +327,19 @@ class TypingWriterHandler(FollowerTypingHandler):
         room_id = content["room_id"]
         user_id = content["user_id"]
 
+        # If we're not in the room just ditch the event entirely. This is
+        # probably an old server that has come back and thinks we're still in
+        # the room (or we've been rejoined to the room by a state reset).
+        is_in_room = await self.event_auth_handler.check_host_in_room(
+            room_id, self.server_name
+        )
+        if not is_in_room:
+            logger.info(
+                "Ignoring typing update from %s as we're not in the room",
+                origin,
+            )
+            return
+
         member = RoomMember(user_id=user_id, room_id=room_id)
 
         # Check that the string is a valid user id
@@ -391,9 +405,9 @@ class TypingWriterHandler(FollowerTypingHandler):
         if last_id == current_id:
             return [], current_id, False
 
-        changed_rooms = self._typing_stream_change_cache.get_all_entities_changed(
-            last_id
-        )  # type: Optional[Iterable[str]]
+        changed_rooms: Optional[
+            Iterable[str]
+        ] = self._typing_stream_change_cache.get_all_entities_changed(last_id)
 
         if changed_rooms is None:
             changed_rooms = self._room_serials