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Update get_pdu to return the original, pristine EventBase (#13320)

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Update `get_pdu` to return the untouched, pristine `EventBase` as it was originally seen over federation (no metadata added). Previously, we returned the same `event` reference that we stored in the cache which downstream code modified in place and added metadata like setting it as an `outlier`  and essentially poisoned our cache. Now we always return a copy of the `event` so the original can stay pristine in our cache and re-used for the next cache call.

Split out from https://github.com/matrix-org/synapse/pull/13205

As discussed at:

 - https://github.com/matrix-org/synapse/pull/13205#discussion_r918365746
 - https://github.com/matrix-org/synapse/pull/13205#discussion_r918366125

Related to https://github.com/matrix-org/synapse/issues/12584. This PR doesn't fix that issue because it hits [`get_event` which exists from the local database before it tries to `get_pdu`](7864f33e28/synapse/federation/federation_client.py (L581-L594)).
This commit is contained in:
Eric Eastwood 2022-07-20 15:58:51 -05:00 committed by GitHub
parent a1b62af2af
commit 0f971ca68e
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5 changed files with 232 additions and 60 deletions
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1
changelog.d/13320.misc Normal file
View file

@ -0,0 +1 @@
Fix `FederationClient.get_pdu()` returning events from the cache as `outliers` instead of original events we saw over federation.

65
synapse/federation/federation_client.py
View file

@ -53,7 +53,7 @@ from synapse.api.room_versions import (
RoomVersion,
RoomVersions,
)
from synapse.events import EventBase, builder
from synapse.events import EventBase, builder, make_event_from_dict
from synapse.federation.federation_base import (
FederationBase,
InvalidEventSignatureError,
@ -299,7 +299,8 @@ class FederationClient(FederationBase):
moving to the next destination. None indicates no timeout.
Returns:
The requested PDU, or None if we were unable to find it.
A copy of the requested PDU that is safe to modify, or None if we
were unable to find it.
Raises:
SynapseError, NotRetryingDestination, FederationDeniedError
@ -309,7 +310,7 @@ class FederationClient(FederationBase):
)
logger.debug(
"retrieved event id %s from %s: %r",
"get_pdu_from_destination_raw: retrieved event id %s from %s: %r",
event_id,
destination,
transaction_data,
@ -358,23 +359,38 @@ class FederationClient(FederationBase):
The requested PDU, or None if we were unable to find it.
"""
logger.debug(
"get_pdu: event_id=%s from destinations=%s", event_id, destinations
)
# TODO: Rate limit the number of times we try and get the same event.
ev = self._get_pdu_cache.get(event_id)
if ev:
return ev
# We might need the same event multiple times in quick succession (before
# it gets persisted to the database), so we cache the results of the lookup.
# Note that this is separate to the regular get_event cache which caches
# events once they have been persisted.
event = self._get_pdu_cache.get(event_id)
# If we don't see the event in the cache, go try to fetch it from the
# provided remote federated destinations
if not event:
pdu_attempts = self.pdu_destination_tried.setdefault(event_id, {})
signed_pdu = None
for destination in destinations:
now = self._clock.time_msec()
last_attempt = pdu_attempts.get(destination, 0)
if last_attempt + PDU_RETRY_TIME_MS > now:
logger.debug(
"get_pdu: skipping destination=%s because we tried it recently last_attempt=%s and we only check every %s (now=%s)",
destination,
last_attempt,
PDU_RETRY_TIME_MS,
now,
)
continue
try:
signed_pdu = await self.get_pdu_from_destination_raw(
event = await self.get_pdu_from_destination_raw(
destination=destination,
event_id=event_id,
room_version=room_version,
@ -383,9 +399,20 @@ class FederationClient(FederationBase):
pdu_attempts[destination] = now
if event:
# Prime the cache
self._get_pdu_cache[event.event_id] = event
# FIXME: We should add a `break` here to avoid calling every
# destination after we already found a PDU (will follow-up
# in a separate PR)
except SynapseError as e:
logger.info(
"Failed to get PDU %s from %s because %s", event_id, destination, e
"Failed to get PDU %s from %s because %s",
event_id,
destination,
e,
)
continue
except NotRetryingDestination as e:
@ -398,14 +425,26 @@ class FederationClient(FederationBase):
pdu_attempts[destination] = now
logger.info(
"Failed to get PDU %s from %s because %s", event_id, destination, e
"Failed to get PDU %s from %s because %s",
event_id,
destination,
e,
)
continue
if signed_pdu:
self._get_pdu_cache[event_id] = signed_pdu
if not event:
return None
return signed_pdu
# `event` now refers to an object stored in `get_pdu_cache`. Our
# callers may need to modify the returned object (eg to set
# `event.internal_metadata.outlier = true`), so we return a copy
# rather than the original object.
event_copy = make_event_from_dict(
event.get_pdu_json(),
event.room_version,
)
return event_copy
async def get_room_state_ids(
self, destination: str, room_id: str, event_id: str

22
synapse/handlers/federation_event.py
View file

@ -766,10 +766,24 @@ class FederationEventHandler:
"""
logger.info("Processing pulled event %s", event)
# these should not be outliers.
assert (
not event.internal_metadata.is_outlier()
), "pulled event unexpectedly flagged as outlier"
# This function should not be used to persist outliers (use something
# else) because this does a bunch of operations that aren't necessary
# (extra work; in particular, it makes sure we have all the prev_events
# and resolves the state across those prev events). If you happen to run
# into a situation where the event you're trying to process/backfill is
# marked as an `outlier`, then you should update that spot to return an
# `EventBase` copy that doesn't have `outlier` flag set.
#
# `EventBase` is used to represent both an event we have not yet
# persisted, and one that we have persisted and now keep in the cache.
# In an ideal world this method would only be called with the first type
# of event, but it turns out that's not actually the case and for
# example, you could get an event from cache that is marked as an
# `outlier` (fix up that spot though).
assert not event.internal_metadata.is_outlier(), (
"Outlier event passed to _process_pulled_event. "
"To persist an event as a non-outlier, make sure to pass in a copy without `event.internal_metadata.outlier = true`."
)
event_id = event.event_id

23
synapse/storage/databases/main/events.py
View file

@ -1346,9 +1346,24 @@ class PersistEventsStore:
event_id: outlier for event_id, outlier in txn
}
logger.debug(
"_update_outliers_txn: events=%s have_persisted=%s",
[ev.event_id for ev, _ in events_and_contexts],
have_persisted,
)
to_remove = set()
for event, context in events_and_contexts:
if event.event_id not in have_persisted:
outlier_persisted = have_persisted.get(event.event_id)
logger.debug(
"_update_outliers_txn: event=%s outlier=%s outlier_persisted=%s",
event.event_id,
event.internal_metadata.is_outlier(),
outlier_persisted,
)
# Ignore events which we haven't persisted at all
if outlier_persisted is None:
continue
to_remove.add(event)
@ -1358,7 +1373,6 @@ class PersistEventsStore:
# was an outlier or not - what we have is at least as good.
continue
outlier_persisted = have_persisted[event.event_id]
if not event.internal_metadata.is_outlier() and outlier_persisted:
# We received a copy of an event that we had already stored as
# an outlier in the database. We now have some state at that event
@ -1369,7 +1383,10 @@ class PersistEventsStore:
# events down /sync. In general they will be historical events, so that
# doesn't matter too much, but that is not always the case.
logger.info("Updating state for ex-outlier event %s", event.event_id)
logger.info(
"_update_outliers_txn: Updating state for ex-outlier event %s",
event.event_id,
)
# insert into event_to_state_groups.
try:

125
tests/federation/test_federation_client.py
View file

@ -22,6 +22,7 @@ from twisted.python.failure import Failure
from twisted.test.proto_helpers import MemoryReactor
from synapse.api.room_versions import RoomVersions
from synapse.events import EventBase
from synapse.server import HomeServer
from synapse.types import JsonDict
from synapse.util import Clock
@ -38,20 +39,24 @@ class FederationClientTest(FederatingHomeserverTestCase):
self._mock_agent = mock.create_autospec(twisted.web.client.Agent, spec_set=True)
homeserver.get_federation_http_client().agent = self._mock_agent
def test_get_room_state(self):
creator = f"@creator:{self.OTHER_SERVER_NAME}"
test_room_id = "!room_id"
# Move clock up to somewhat realistic time so the PDU destination retry
# works (`now` needs to be larger than `0 + PDU_RETRY_TIME_MS`).
self.reactor.advance(1000000000)
self.creator = f"@creator:{self.OTHER_SERVER_NAME}"
self.test_room_id = "!room_id"
def test_get_room_state(self):
# mock up some events to use in the response.
# In real life, these would have things in `prev_events` and `auth_events`, but that's
# a bit annoying to mock up, and the code under test doesn't care, so we don't bother.
create_event_dict = self.add_hashes_and_signatures_from_other_server(
{
"room_id": test_room_id,
"room_id": self.test_room_id,
"type": "m.room.create",
"state_key": "",
"sender": creator,
"content": {"creator": creator},
"sender": self.creator,
"content": {"creator": self.creator},
"prev_events": [],
"auth_events": [],
"origin_server_ts": 500,
@ -59,10 +64,10 @@ class FederationClientTest(FederatingHomeserverTestCase):
)
member_event_dict = self.add_hashes_and_signatures_from_other_server(
{
"room_id": test_room_id,
"room_id": self.test_room_id,
"type": "m.room.member",
"sender": creator,
"state_key": creator,
"sender": self.creator,
"state_key": self.creator,
"content": {"membership": "join"},
"prev_events": [],
"auth_events": [],
@ -71,9 +76,9 @@ class FederationClientTest(FederatingHomeserverTestCase):
)
pl_event_dict = self.add_hashes_and_signatures_from_other_server(
{
"room_id": test_room_id,
"room_id": self.test_room_id,
"type": "m.room.power_levels",
"sender": creator,
"sender": self.creator,
"state_key": "",
"content": {},
"prev_events": [],
@ -103,7 +108,7 @@ class FederationClientTest(FederatingHomeserverTestCase):
state_resp, auth_resp = self.get_success(
self.hs.get_federation_client().get_room_state(
"yet.another.server",
test_room_id,
self.test_room_id,
"event_id",
RoomVersions.V9,
)
@ -130,6 +135,102 @@ class FederationClientTest(FederatingHomeserverTestCase):
["m.room.create", "m.room.member", "m.room.power_levels"],
)
def test_get_pdu_returns_nothing_when_event_does_not_exist(self):
"""No event should be returned when the event does not exist"""
remote_pdu = self.get_success(
self.hs.get_federation_client().get_pdu(
["yet.another.server"],
"event_should_not_exist",
RoomVersions.V9,
)
)
self.assertEqual(remote_pdu, None)
def test_get_pdu(self):
"""Test to make sure an event is returned by `get_pdu()`"""
self._get_pdu_once()
def test_get_pdu_event_from_cache_is_pristine(self):
"""Test that modifications made to events returned by `get_pdu()`
do not propagate back to to the internal cache (events returned should
be a copy).
"""
# Get the PDU in the cache
remote_pdu = self._get_pdu_once()
# Modify the the event reference.
# This change should not make it back to the `_get_pdu_cache`.
remote_pdu.internal_metadata.outlier = True
# Get the event again. This time it should read it from cache.
remote_pdu2 = self.get_success(
self.hs.get_federation_client().get_pdu(
["yet.another.server"],
remote_pdu.event_id,
RoomVersions.V9,
)
)
# Sanity check that we are working against the same event
self.assertEqual(remote_pdu.event_id, remote_pdu2.event_id)
# Make sure the event does not include modification from earlier
self.assertIsNotNone(remote_pdu2)
self.assertEqual(remote_pdu2.internal_metadata.outlier, False)
def _get_pdu_once(self) -> EventBase:
"""Retrieve an event via `get_pdu()` and assert that an event was returned.
Also used to prime the cache for subsequent test logic.
"""
message_event_dict = self.add_hashes_and_signatures_from_other_server(
{
"room_id": self.test_room_id,
"type": "m.room.message",
"sender": self.creator,
"state_key": "",
"content": {},
"prev_events": [],
"auth_events": [],
"origin_server_ts": 700,
"depth": 10,
}
)
# mock up the response, and have the agent return it
self._mock_agent.request.side_effect = lambda *args, **kwargs: defer.succeed(
_mock_response(
{
"origin": "yet.another.server",
"origin_server_ts": 900,
"pdus": [
message_event_dict,
],
}
)
)
remote_pdu = self.get_success(
self.hs.get_federation_client().get_pdu(
["yet.another.server"],
"event_id",
RoomVersions.V9,
)
)
# check the right call got made to the agent
self._mock_agent.request.assert_called_once_with(
b"GET",
b"matrix://yet.another.server/_matrix/federation/v1/event/event_id",
headers=mock.ANY,
bodyProducer=None,
)
self.assertIsNotNone(remote_pdu)
self.assertEqual(remote_pdu.internal_metadata.outlier, False)
return remote_pdu
def _mock_response(resp: JsonDict):
body = json.dumps(resp).encode("utf-8")