Factor out `_send_dummy_event_for_room` (#8370)

this makes it possible to use from the manhole, and seems cleaner anyway.

changelog.d/8370.misc

@@ -0,0 +1 @@
+Factor out a `_send_dummy_event_for_room` method.

synapse/handlers/message.py

@@ -1182,15 +1182,36 @@ class EventCreationHandler:
         )
 
         for room_id in room_ids:
+            dummy_event_sent = await self._send_dummy_event_for_room(room_id)
+
+            if not dummy_event_sent:
+                # Did not find a valid user in the room, so remove from future attempts
+                # Exclusion is time limited, so the room will be rechecked in the future
+                # dependent on _DUMMY_EVENT_ROOM_EXCLUSION_EXPIRY
+                logger.info(
+                    "Failed to send dummy event into room %s. Will exclude it from "
+                    "future attempts until cache expires" % (room_id,)
+                )
+                now = self.clock.time_msec()
+                self._rooms_to_exclude_from_dummy_event_insertion[room_id] = now
+
+    async def _send_dummy_event_for_room(self, room_id: str) -> bool:
+        """Attempt to send a dummy event for the given room.
+
+        Args:
+            room_id: room to try to send an event from
+
+        Returns:
+            True if a dummy event was successfully sent. False if no user was able
+            to send an event.
+        """
+
         # For each room we need to find a joined member we can use to send
         # the dummy event with.
-
         latest_event_ids = await self.store.get_prev_events_for_room(room_id)
-
         members = await self.state.get_current_users_in_room(
             room_id, latest_event_ids=latest_event_ids
         )
-            dummy_event_sent = False
         for user_id in members:
             if not self.hs.is_mine_id(user_id):
                 continue
@@ -1212,14 +1233,9 @@ class EventCreationHandler:
                 # Since this is a dummy-event it is OK if it is sent by a
                 # shadow-banned user.
                 await self.send_nonmember_event(
-                        requester,
+                    requester, event, context, ratelimit=False, ignore_shadow_ban=True,
-                        event,
-                        context,
-                        ratelimit=False,
-                        ignore_shadow_ban=True,
                 )
-                    dummy_event_sent = True
+                return True
-                    break
             except ConsentNotGivenError:
                 logger.info(
                     "Failed to send dummy event into room %s for user %s due to "
@@ -1230,17 +1246,7 @@ class EventCreationHandler:
                     "Failed to send dummy event into room %s for user %s due to "
                     "lack of power. Will try another user" % (room_id, user_id)
                 )
-
+        return False
-            if not dummy_event_sent:
-                # Did not find a valid user in the room, so remove from future attempts
-                # Exclusion is time limited, so the room will be rechecked in the future
-                # dependent on _DUMMY_EVENT_ROOM_EXCLUSION_EXPIRY
-                logger.info(
-                    "Failed to send dummy event into room %s. Will exclude it from "
-                    "future attempts until cache expires" % (room_id,)
-                )
-                now = self.clock.time_msec()
-                self._rooms_to_exclude_from_dummy_event_insertion[room_id] = now
 
     def _expire_rooms_to_exclude_from_dummy_event_insertion(self):
         expire_before = self.clock.time_msec() - _DUMMY_EVENT_ROOM_EXCLUSION_EXPIRY