typing: check origin server of typing event against room's servers

changelog.d/13830.bugfix

@@ -0,0 +1 @@
+Fix a long-standing bug where typing events would be accepted from remote servers not present in a room. Also fix a bug where incoming typing events would cause other incoming events to get stuck during a fast join.

synapse/handlers/typing.py

@@ -362,11 +362,14 @@ async def _recv_edu(self, origin: str, content: JsonDict) -> None:
             )
             return
 
-        domains = await self._storage_controllers.state.get_current_hosts_in_room(
+        # Let's check that the origin server is in the room before accepting the typing
+        # event. We don't want to block waiting on a partial state so take an
+        # approximation if needed.
+        domains = await self._storage_controllers.state.get_current_hosts_in_room_or_partial_state_approximation(
             room_id
         )
 
-        if self.server_name in domains:
+        if user.domain in domains:
             logger.info("Got typing update from %s: %r", user_id, content)
             now = self.clock.time_msec()
             self._member_typing_until[member] = now + FEDERATION_TIMEOUT