diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index a257d87fed..529d025c39 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -285,169 +285,172 @@ class FederationHandler(BaseHandler):
# - Fetching any missing prev events to fill in gaps in the graph
# - Fetching state if we have a hole in the graph
if not pdu.internal_metadata.is_outlier():
- # We only backfill backwards to the min depth.
- min_depth = await self.get_min_depth_for_context(pdu.room_id)
-
- logger.debug("min_depth: %d", min_depth)
-
prevs = set(pdu.prev_event_ids())
seen = await self.store.have_events_in_timeline(prevs)
+ missing_prevs = prevs - seen
- if min_depth is not None and pdu.depth > min_depth:
- missing_prevs = prevs - seen
- if sent_to_us_directly and missing_prevs:
- # If we're missing stuff, ensure we only fetch stuff one
- # at a time.
- logger.info(
- "Acquiring room lock to fetch %d missing prev_events: %s",
- len(missing_prevs),
- shortstr(missing_prevs),
- )
- with (await self._room_pdu_linearizer.queue(pdu.room_id)):
+ if missing_prevs:
+ if sent_to_us_directly:
+ # We only backfill backwards to the min depth.
+ min_depth = await self.get_min_depth_for_context(pdu.room_id)
+ logger.debug("min_depth: %d", min_depth)
+
+ if min_depth is not None and pdu.depth > min_depth:
+ # If we're missing stuff, ensure we only fetch stuff one
+ # at a time.
logger.info(
- "Acquired room lock to fetch %d missing prev_events",
+ "Acquiring room lock to fetch %d missing prev_events: %s",
len(missing_prevs),
+ shortstr(missing_prevs),
)
-
- try:
- await self._get_missing_events_for_pdu(
- origin, pdu, prevs, min_depth
+ with (await self._room_pdu_linearizer.queue(pdu.room_id)):
+ logger.info(
+ "Acquired room lock to fetch %d missing prev_events",
+ len(missing_prevs),
)
- except Exception as e:
- raise Exception(
- "Error fetching missing prev_events for %s: %s"
- % (event_id, e)
- ) from e
+
+ try:
+ await self._get_missing_events_for_pdu(
+ origin, pdu, prevs, min_depth
+ )
+ except Exception as e:
+ raise Exception(
+ "Error fetching missing prev_events for %s: %s"
+ % (event_id, e)
+ ) from e
# Update the set of things we've seen after trying to
# fetch the missing stuff
seen = await self.store.have_events_in_timeline(prevs)
+ missing_prevs = prevs - seen
+
+ if not missing_prevs:
+ logger.info("Found all missing prev_events")
+
+ if missing_prevs:
+ # since this event was pushed to us, it is possible for it to
+ # become the only forward-extremity in the room, and we would then
+ # trust its state to be the state for the whole room. This is very
+ # bad. Further, if the event was pushed to us, there is no excuse
+ # for us not to have all the prev_events. (XXX: apart from
+ # min_depth?)
+ #
+ # We therefore reject any such events.
+ logger.warning(
+ "Rejecting: failed to fetch %d prev events: %s",
+ len(missing_prevs),
+ shortstr(missing_prevs),
+ )
+ raise FederationError(
+ "ERROR",
+ 403,
+ (
+ "Your server isn't divulging details about prev_events "
+ "referenced in this event."
+ ),
+ affected=pdu.event_id,
+ )
- if not prevs - seen:
- logger.info(
- "Found all missing prev_events",
- )
-
- missing_prevs = prevs - seen
- if missing_prevs:
- # We've still not been able to get all of the prev_events for this event.
- #
- # In this case, we need to fall back to asking another server in the
- # federation for the state at this event. That's ok provided we then
- # resolve the state against other bits of the DAG before using it (which
- # will ensure that you can't just take over a room by sending an event,
- # withholding its prev_events, and declaring yourself to be an admin in
- # the subsequent state request).
- #
- # Now, if we're pulling this event as a missing prev_event, then clearly
- # this event is not going to become the only forward-extremity and we are
- # guaranteed to resolve its state against our existing forward
- # extremities, so that should be fine.
- #
- # On the other hand, if this event was pushed to us, it is possible for
- # it to become the only forward-extremity in the room, and we would then
- # trust its state to be the state for the whole room. This is very bad.
- # Further, if the event was pushed to us, there is no excuse for us not to
- # have all the prev_events. We therefore reject any such events.
- #
- # XXX this really feels like it could/should be merged with the above,
- # but there is an interaction with min_depth that I'm not really
- # following.
-
- if sent_to_us_directly:
- logger.warning(
- "Rejecting: failed to fetch %d prev events: %s",
- len(missing_prevs),
+ else:
+ # We don't have all of the prev_events for this event.
+ #
+ # In this case, we need to fall back to asking another server in the
+ # federation for the state at this event. That's ok provided we then
+ # resolve the state against other bits of the DAG before using it (which
+ # will ensure that you can't just take over a room by sending an event,
+ # withholding its prev_events, and declaring yourself to be an admin in
+ # the subsequent state request).
+ #
+ # Since we're pulling this event as a missing prev_event, then clearly
+ # this event is not going to become the only forward-extremity and we are
+ # guaranteed to resolve its state against our existing forward
+ # extremities, so that should be fine.
+ #
+ # XXX this really feels like it could/should be merged with the above,
+ # but there is an interaction with min_depth that I'm not really
+ # following.
+ logger.info(
+ "Event %s is missing prev_events %s: calculating state for a "
+ "backwards extremity",
+ event_id,
shortstr(missing_prevs),
)
- raise FederationError(
- "ERROR",
- 403,
- (
- "Your server isn't divulging details about prev_events "
- "referenced in this event."
- ),
- affected=pdu.event_id,
- )
- logger.info(
- "Event %s is missing prev_events %s: calculating state for a "
- "backwards extremity",
- event_id,
- shortstr(missing_prevs),
- )
+ # Calculate the state after each of the previous events, and
+ # resolve them to find the correct state at the current event.
+ event_map = {event_id: pdu}
+ try:
+ # Get the state of the events we know about
+ ours = await self.state_store.get_state_groups_ids(
+ room_id, seen
+ )
- # Calculate the state after each of the previous events, and
- # resolve them to find the correct state at the current event.
- event_map = {event_id: pdu}
- try:
- # Get the state of the events we know about
- ours = await self.state_store.get_state_groups_ids(room_id, seen)
-
- # state_maps is a list of mappings from (type, state_key) to event_id
- state_maps: List[StateMap[str]] = list(ours.values())
-
- # we don't need this any more, let's delete it.
- del ours
-
- # Ask the remote server for the states we don't
- # know about
- for p in missing_prevs:
- logger.info("Requesting state after missing prev_event %s", p)
-
- with nested_logging_context(p):
- # note that if any of the missing prevs share missing state or
- # auth events, the requests to fetch those events are deduped
- # by the get_pdu_cache in federation_client.
- remote_state = (
- await self._get_state_after_missing_prev_event(
- origin, room_id, p
- )
+ # state_maps is a list of mappings from (type, state_key) to event_id
+ state_maps: List[StateMap[str]] = list(ours.values())
+
+ # we don't need this any more, let's delete it.
+ del ours
+
+ # Ask the remote server for the states we don't
+ # know about
+ for p in missing_prevs:
+ logger.info(
+ "Requesting state after missing prev_event %s", p
)
- remote_state_map = {
- (x.type, x.state_key): x.event_id for x in remote_state
- }
- state_maps.append(remote_state_map)
+ with nested_logging_context(p):
+ # note that if any of the missing prevs share missing state or
+ # auth events, the requests to fetch those events are deduped
+ # by the get_pdu_cache in federation_client.
+ remote_state = (
+ await self._get_state_after_missing_prev_event(
+ origin, room_id, p
+ )
+ )
+
+ remote_state_map = {
+ (x.type, x.state_key): x.event_id
+ for x in remote_state
+ }
+ state_maps.append(remote_state_map)
- for x in remote_state:
- event_map[x.event_id] = x
+ for x in remote_state:
+ event_map[x.event_id] = x
- room_version = await self.store.get_room_version_id(room_id)
- state_map = (
- await self._state_resolution_handler.resolve_events_with_store(
+ room_version = await self.store.get_room_version_id(room_id)
+ state_map = await self._state_resolution_handler.resolve_events_with_store(
room_id,
room_version,
state_maps,
event_map,
state_res_store=StateResolutionStore(self.store),
)
- )
- # We need to give _process_received_pdu the actual state events
- # rather than event ids, so generate that now.
+ # We need to give _process_received_pdu the actual state events
+ # rather than event ids, so generate that now.
- # First though we need to fetch all the events that are in
- # state_map, so we can build up the state below.
- evs = await self.store.get_events(
- list(state_map.values()),
- get_prev_content=False,
- redact_behaviour=EventRedactBehaviour.AS_IS,
- )
- event_map.update(evs)
+ # First though we need to fetch all the events that are in
+ # state_map, so we can build up the state below.
+ evs = await self.store.get_events(
+ list(state_map.values()),
+ get_prev_content=False,
+ redact_behaviour=EventRedactBehaviour.AS_IS,
+ )
+ event_map.update(evs)
- state = [event_map[e] for e in state_map.values()]
- except Exception:
- logger.warning(
- "Error attempting to resolve state at missing " "prev_events",
- exc_info=True,
- )
- raise FederationError(
- "ERROR",
- 403,
- "We can't get valid state history.",
- affected=event_id,
- )
+ state = [event_map[e] for e in state_map.values()]
+ except Exception:
+ logger.warning(
+ "Error attempting to resolve state at missing "
+ "prev_events",
+ exc_info=True,
+ )
+ raise FederationError(
+ "ERROR",
+ 403,
+ "We can't get valid state history.",
+ affected=event_id,
+ )
# A second round of checks for all events. Check that the event passes auth
# based on `auth_events`, this allows us to assert that the event would
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