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Refactor on_receive_pdu code (#10615)

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* drop room pdu linearizer sooner

No point holding onto it while we recheck the db

* move out `missing_prevs` calculation

we're going to need `missing_prevs` whatever we do, so we may as well calculate
it eagerly and just update it if it gets outdated.

* Add another `if missing_prevs` condition

this should be a no-op, since all the code inside the block already checks `if
missing_prevs`

* reorder if conditions

This shouldn't change the logic at all.

* Push down `min_depth` read

No point reading it from the database unless we're going to use it.

* Collect the sent_to_us_directly code together

Move the remaining `sent_to_us_directly` code inside the `if
sent_to_us_directly` block.

* Properly separate the `not sent_to_us_directly` branch

Since the only way this second block is now reachable is if we
*didn't* go into the `sent_to_us_directly` branch, we can replace it with a
simple `else`.

* changelog
This commit is contained in:
Richard van der Hoff 2021-08-18 12:36:22 +01:00 committed by GitHub
parent 6a5f8fbcda
commit 964f29cb6f
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2 changed files with 134 additions and 130 deletions
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changelog.d/10615.misc Normal file
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@ -0,0 +1 @@
Clean up some of the federation event authentication code for clarity.

93
synapse/handlers/federation.py
View File

@ -285,17 +285,17 @@ 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 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:
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(
@ -322,39 +322,20 @@ class FederationHandler(BaseHandler):
# Update the set of things we've seen after trying to
# fetch the missing stuff
seen = await self.store.have_events_in_timeline(prevs)
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:
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),
@ -370,6 +351,24 @@ class FederationHandler(BaseHandler):
affected=pdu.event_id,
)
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",
@ -382,7 +381,9 @@ class FederationHandler(BaseHandler):
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)
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())
@ -393,7 +394,9 @@ class FederationHandler(BaseHandler):
# 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)
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
@ -406,7 +409,8 @@ class FederationHandler(BaseHandler):
)
remote_state_map = {
(x.type, x.state_key): x.event_id for x in remote_state
(x.type, x.state_key): x.event_id
for x in remote_state
}
state_maps.append(remote_state_map)
@ -414,15 +418,13 @@ class FederationHandler(BaseHandler):
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(
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.
@ -439,7 +441,8 @@ class FederationHandler(BaseHandler):
state = [event_map[e] for e in state_map.values()]
except Exception:
logger.warning(
"Error attempting to resolve state at missing " "prev_events",
"Error attempting to resolve state at missing "
"prev_events",
exc_info=True,
)
raise FederationError(