Extract `_resolve_state_at_missing_prevs` (#10624)
This is a follow-up to #10615: it takes the code that constructs the state at a backwards extremity, and extracts it to a separate method.
This commit is contained in:
Richard van der Hoff
GitHub
parent
000aa89be6
commit
50af1efe4b
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Clean up some of the federation event authentication code for clarity.
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@ -285,12 +285,12 @@ class FederationHandler(BaseHandler):
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# - Fetching any missing prev events to fill in gaps in the graph
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# - Fetching state if we have a hole in the graph
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if not pdu.internal_metadata.is_outlier():
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prevs = set(pdu.prev_event_ids())
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seen = await self.store.have_events_in_timeline(prevs)
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missing_prevs = prevs - seen
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if sent_to_us_directly:
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prevs = set(pdu.prev_event_ids())
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seen = await self.store.have_events_in_timeline(prevs)
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missing_prevs = prevs - seen
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if missing_prevs:
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if sent_to_us_directly:
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if missing_prevs:
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# We only backfill backwards to the min depth.
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min_depth = await self.get_min_depth_for_context(pdu.room_id)
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logger.debug("min_depth: %d", min_depth)
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@ -351,106 +351,8 @@ class FederationHandler(BaseHandler):
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affected=pdu.event_id,
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)
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else:
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# We don't have all of the prev_events for this event.
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#
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# In this case, we need to fall back to asking another server in the
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# federation for the state at this event. That's ok provided we then
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# resolve the state against other bits of the DAG before using it (which
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# will ensure that you can't just take over a room by sending an event,
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# withholding its prev_events, and declaring yourself to be an admin in
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# the subsequent state request).
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#
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# Since we're pulling this event as a missing prev_event, then clearly
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# this event is not going to become the only forward-extremity and we are
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# guaranteed to resolve its state against our existing forward
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# extremities, so that should be fine.
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#
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# XXX this really feels like it could/should be merged with the above,
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# but there is an interaction with min_depth that I'm not really
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# following.
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logger.info(
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"Event %s is missing prev_events %s: calculating state for a "
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"backwards extremity",
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event_id,
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shortstr(missing_prevs),
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)
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# Calculate the state after each of the previous events, and
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# resolve them to find the correct state at the current event.
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event_map = {event_id: pdu}
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try:
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# Get the state of the events we know about
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ours = await self.state_store.get_state_groups_ids(
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room_id, seen
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)
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# state_maps is a list of mappings from (type, state_key) to event_id
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state_maps: List[StateMap[str]] = list(ours.values())
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# we don't need this any more, let's delete it.
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del ours
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# Ask the remote server for the states we don't
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# know about
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for p in missing_prevs:
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logger.info(
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"Requesting state after missing prev_event %s", p
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)
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with nested_logging_context(p):
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# note that if any of the missing prevs share missing state or
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# auth events, the requests to fetch those events are deduped
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# by the get_pdu_cache in federation_client.
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remote_state = (
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await self._get_state_after_missing_prev_event(
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origin, room_id, p
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)
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)
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remote_state_map = {
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(x.type, x.state_key): x.event_id
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for x in remote_state
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}
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state_maps.append(remote_state_map)
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for x in remote_state:
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event_map[x.event_id] = x
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room_version = await self.store.get_room_version_id(room_id)
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state_map = await self._state_resolution_handler.resolve_events_with_store(
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room_id,
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room_version,
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state_maps,
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event_map,
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state_res_store=StateResolutionStore(self.store),
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)
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# We need to give _process_received_pdu the actual state events
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# rather than event ids, so generate that now.
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# First though we need to fetch all the events that are in
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# state_map, so we can build up the state below.
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evs = await self.store.get_events(
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list(state_map.values()),
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get_prev_content=False,
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redact_behaviour=EventRedactBehaviour.AS_IS,
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)
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event_map.update(evs)
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state = [event_map[e] for e in state_map.values()]
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except Exception:
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logger.warning(
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"Error attempting to resolve state at missing "
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"prev_events",
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exc_info=True,
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)
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raise FederationError(
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"ERROR",
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403,
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"We can't get valid state history.",
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affected=event_id,
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)
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else:
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state = await self._resolve_state_at_missing_prevs(origin, pdu)
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# A second round of checks for all events. Check that the event passes auth
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# based on `auth_events`, this allows us to assert that the event would
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@ -1493,6 +1395,123 @@ class FederationHandler(BaseHandler):
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event_infos,
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)
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async def _resolve_state_at_missing_prevs(
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self, dest: str, event: EventBase
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) -> Optional[Iterable[EventBase]]:
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"""Calculate the state at an event with missing prev_events.
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This is used when we have pulled a batch of events from a remote server, and
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still don't have all the prev_events.
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If we already have all the prev_events for `event`, this method does nothing.
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Otherwise, the missing prevs become new backwards extremities, and we fall back
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to asking the remote server for the state after each missing `prev_event`,
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and resolving across them.
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That's ok provided we then resolve the state against other bits of the DAG
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before using it - in other words, that the received event `event` is not going
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to become the only forwards_extremity in the room (which will ensure that you
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can't just take over a room by sending an event, withholding its prev_events,
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and declaring yourself to be an admin in the subsequent state request).
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In other words: we should only call this method if `event` has been *pulled*
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as part of a batch of missing prev events, or similar.
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Params:
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dest: the remote server to ask for state at the missing prevs. Typically,
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this will be the server we got `event` from.
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event: an event to check for missing prevs.
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Returns:
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if we already had all the prev events, `None`. Otherwise, returns a list of
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the events in the state at `event`.
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"""
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room_id = event.room_id
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event_id = event.event_id
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prevs = set(event.prev_event_ids())
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seen = await self.store.have_events_in_timeline(prevs)
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missing_prevs = prevs - seen
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if not missing_prevs:
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return None
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logger.info(
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"Event %s is missing prev_events %s: calculating state for a "
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"backwards extremity",
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event_id,
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shortstr(missing_prevs),
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)
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# Calculate the state after each of the previous events, and
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# resolve them to find the correct state at the current event.
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event_map = {event_id: event}
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try:
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# Get the state of the events we know about
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ours = await self.state_store.get_state_groups_ids(room_id, seen)
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# state_maps is a list of mappings from (type, state_key) to event_id
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state_maps: List[StateMap[str]] = list(ours.values())
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# we don't need this any more, let's delete it.
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del ours
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# Ask the remote server for the states we don't
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# know about
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for p in missing_prevs:
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logger.info("Requesting state after missing prev_event %s", p)
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with nested_logging_context(p):
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# note that if any of the missing prevs share missing state or
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# auth events, the requests to fetch those events are deduped
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# by the get_pdu_cache in federation_client.
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remote_state = await self._get_state_after_missing_prev_event(
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dest, room_id, p
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)
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remote_state_map = {
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(x.type, x.state_key): x.event_id for x in remote_state
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}
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state_maps.append(remote_state_map)
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for x in remote_state:
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event_map[x.event_id] = x
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room_version = await self.store.get_room_version_id(room_id)
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state_map = await self._state_resolution_handler.resolve_events_with_store(
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room_id,
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room_version,
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state_maps,
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event_map,
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state_res_store=StateResolutionStore(self.store),
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)
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# We need to give _process_received_pdu the actual state events
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# rather than event ids, so generate that now.
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# First though we need to fetch all the events that are in
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# state_map, so we can build up the state below.
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evs = await self.store.get_events(
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list(state_map.values()),
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get_prev_content=False,
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redact_behaviour=EventRedactBehaviour.AS_IS,
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)
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event_map.update(evs)
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state = [event_map[e] for e in state_map.values()]
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except Exception:
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logger.warning(
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"Error attempting to resolve state at missing prev_events",
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exc_info=True,
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)
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raise FederationError(
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"ERROR",
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403,
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"We can't get valid state history.",
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affected=event_id,
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)
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return state
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def _sanity_check_event(self, ev: EventBase) -> None:
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"""
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Do some early sanity checks of a received event
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