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Refactor MSC3030 `/timestamp_to_event` to move away from our snowflake pull from `destination` pattern (#14096) 

1. `federation_client.timestamp_to_event(...)` now handles all `destination` looping and uses our generic `_try_destination_list(...)` helper.
 2. Consistently handling `NotRetryingDestination` and `FederationDeniedError` across `get_pdu` , backfill, and the generic `_try_destination_list` which is used for many places we use this pattern.
 3. `get_pdu(...)` now returns `PulledPduInfo` so we know which `destination` we ended up pulling the PDU from
This commit is contained in:
Eric Eastwood 2022-10-26 16:10:55 -05:00 committed by GitHub
parent 0d59ae706a
commit 40fa8294e3
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7 changed files with 192 additions and 127 deletions
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1
changelog.d/14096.misc Normal file
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@ -0,0 +1 @@
Refactor [MSC3030](https://github.com/matrix-org/matrix-spec-proposals/pull/3030) `/timestamp_to_event` endpoint to loop over federation destinations with standard pattern and error handling.

130
synapse/federation/federation_client.py
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@ -80,6 +80,18 @@ PDU_RETRY_TIME_MS = 1 * 60 * 1000
T = TypeVar("T")
@attr.s(frozen=True, slots=True, auto_attribs=True)
class PulledPduInfo:
"""
A result object that stores the PDU and info about it like which homeserver we
pulled it from (`pull_origin`)
"""
pdu: EventBase
# Which homeserver we pulled the PDU from
pull_origin: str
class InvalidResponseError(RuntimeError):
"""Helper for _try_destination_list: indicates that the server returned a response
we couldn't parse
@ -114,7 +126,9 @@ class FederationClient(FederationBase):
self.hostname = hs.hostname
self.signing_key = hs.signing_key
self._get_pdu_cache: ExpiringCache[str, EventBase] = ExpiringCache(
# Cache mapping `event_id` to a tuple of the event itself and the `pull_origin`
# (which server we pulled the event from)
self._get_pdu_cache: ExpiringCache[str, Tuple[EventBase, str]] = ExpiringCache(
cache_name="get_pdu_cache",
clock=self._clock,
max_len=1000,
@ -352,11 +366,11 @@ class FederationClient(FederationBase):
@tag_args
async def get_pdu(
self,
destinations: Iterable[str],
destinations: Collection[str],
event_id: str,
room_version: RoomVersion,
timeout: Optional[int] = None,
) -> Optional[EventBase]:
) -> Optional[PulledPduInfo]:
"""Requests the PDU with given origin and ID from the remote home
servers.
@ -371,11 +385,11 @@ 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.
The requested PDU wrapped in `PulledPduInfo`, or None if we were unable to find it.
"""
logger.debug(
"get_pdu: event_id=%s from destinations=%s", event_id, destinations
"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.
@ -384,19 +398,25 @@ class FederationClient(FederationBase):
# 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)
get_pdu_cache_entry = self._get_pdu_cache.get(event_id)
event = None
pull_origin = None
if get_pdu_cache_entry:
event, pull_origin = get_pdu_cache_entry
# If we don't see the event in the cache, go try to fetch it from the
# provided remote federated destinations
if not event:
else:
pdu_attempts = self.pdu_destination_tried.setdefault(event_id, {})
# TODO: We can probably refactor this to use `_try_destination_list`
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)",
"get_pdu(event_id=%s): skipping destination=%s because we tried it recently last_attempt=%s and we only check every %s (now=%s)",
event_id,
destination,
last_attempt,
PDU_RETRY_TIME_MS,
@ -411,43 +431,48 @@ class FederationClient(FederationBase):
room_version=room_version,
timeout=timeout,
)
pull_origin = destination
pdu_attempts[destination] = now
if event:
# Prime the cache
self._get_pdu_cache[event.event_id] = event
self._get_pdu_cache[event.event_id] = (event, pull_origin)
# Now that we have an event, we can break out of this
# loop and stop asking other destinations.
break
except NotRetryingDestination as e:
logger.info("get_pdu(event_id=%s): %s", event_id, e)
continue
except FederationDeniedError:
logger.info(
"get_pdu(event_id=%s): Not attempting to fetch PDU from %s because the homeserver is not on our federation whitelist",
event_id,
destination,
)
continue
except SynapseError as e:
logger.info(
"Failed to get PDU %s from %s because %s",
"get_pdu(event_id=%s): Failed to get PDU from %s because %s",
event_id,
destination,
e,
)
continue
except NotRetryingDestination as e:
logger.info(str(e))
continue
except FederationDeniedError as e:
logger.info(str(e))
continue
except Exception as e:
pdu_attempts[destination] = now
logger.info(
"Failed to get PDU %s from %s because %s",
"get_pdu(event_id=): Failed to get PDU from %s because %s",
event_id,
destination,
e,
)
continue
if not event:
if not event or not pull_origin:
return None
# `event` now refers to an object stored in `get_pdu_cache`. Our
@ -459,7 +484,7 @@ class FederationClient(FederationBase):
event.room_version,
)
return event_copy
return PulledPduInfo(event_copy, pull_origin)
@trace
@tag_args
@ -699,12 +724,14 @@ class FederationClient(FederationBase):
pdu_origin = get_domain_from_id(pdu.sender)
if not res and pdu_origin != origin:
try:
res = await self.get_pdu(
pulled_pdu_info = await self.get_pdu(
destinations=[pdu_origin],
event_id=pdu.event_id,
room_version=room_version,
timeout=10000,
)
if pulled_pdu_info is not None:
res = pulled_pdu_info.pdu
except SynapseError:
pass
@ -806,6 +833,7 @@ class FederationClient(FederationBase):
)
for destination in destinations:
# We don't want to ask our own server for information we don't have
if destination == self.server_name:
continue
@ -814,9 +842,21 @@ class FederationClient(FederationBase):
except (
RequestSendFailed,
InvalidResponseError,
NotRetryingDestination,
) as e:
logger.warning("Failed to %s via %s: %s", description, destination, e)
# Skip to the next homeserver in the list to try.
continue
except NotRetryingDestination as e:
logger.info("%s: %s", description, e)
continue
except FederationDeniedError:
logger.info(
"%s: Not attempting to %s from %s because the homeserver is not on our federation whitelist",
description,
description,
destination,
)
continue
except UnsupportedRoomVersionError:
raise
except HttpResponseException as e:
@ -1609,6 +1649,54 @@ class FederationClient(FederationBase):
return result
async def timestamp_to_event(
self, *, destinations: List[str], room_id: str, timestamp: int, direction: str
) -> Optional["TimestampToEventResponse"]:
"""
Calls each remote federating server from `destinations` asking for their closest
event to the given timestamp in the given direction until we get a response.
Also validates the response to always return the expected keys or raises an
error.
Args:
destinations: The domains of homeservers to try fetching from
room_id: Room to fetch the event from
timestamp: The point in time (inclusive) we should navigate from in
the given direction to find the closest event.
direction: ["f"|"b"] to indicate whether we should navigate forward
or backward from the given timestamp to find the closest event.
Returns:
A parsed TimestampToEventResponse including the closest event_id
and origin_server_ts or None if no destination has a response.
"""
async def _timestamp_to_event_from_destination(
destination: str,
) -> TimestampToEventResponse:
return await self._timestamp_to_event_from_destination(
destination, room_id, timestamp, direction
)
try:
# Loop through each homeserver candidate until we get a succesful response
timestamp_to_event_response = await self._try_destination_list(
"timestamp_to_event",
destinations,
# TODO: The requested timestamp may lie in a part of the
# event graph that the remote server *also* didn't have,
# in which case they will have returned another event
# which may be nowhere near the requested timestamp. In
# the future, we may need to reconcile that gap and ask
# other homeservers, and/or extend `/timestamp_to_event`
# to return events on *both* sides of the timestamp to
# help reconcile the gap faster.
_timestamp_to_event_from_destination,
)
return timestamp_to_event_response
except SynapseError:
return None
async def _timestamp_to_event_from_destination(
self, destination: str, room_id: str, timestamp: int, direction: str
) -> "TimestampToEventResponse":
"""

15
synapse/handlers/federation.py
View File

@ -442,6 +442,15 @@ class FederationHandler:
# appropriate stuff.
# TODO: We can probably do something more intelligent here.
return True
except NotRetryingDestination as e:
logger.info("_maybe_backfill_inner: %s", e)
continue
except FederationDeniedError:
logger.info(
"_maybe_backfill_inner: Not attempting to backfill from %s because the homeserver is not on our federation whitelist",
dom,
)
continue
except (SynapseError, InvalidResponseError) as e:
logger.info("Failed to backfill from %s because %s", dom, e)
continue
@ -477,15 +486,9 @@ class FederationHandler:
logger.info("Failed to backfill from %s because %s", dom, e)
continue
except NotRetryingDestination as e:
logger.info(str(e))
continue
except RequestSendFailed as e:
logger.info("Failed to get backfill from %s because %s", dom, e)
continue
except FederationDeniedError as e:
logger.info(e)
continue
except Exception as e:
logger.exception("Failed to backfill from %s because %s", dom, e)
continue

31
synapse/handlers/federation_event.py
View File

@ -58,7 +58,7 @@ from synapse.event_auth import (
)
from synapse.events import EventBase
from synapse.events.snapshot import EventContext
from synapse.federation.federation_client import InvalidResponseError
from synapse.federation.federation_client import InvalidResponseError, PulledPduInfo
from synapse.logging.context import nested_logging_context
from synapse.logging.opentracing import (
SynapseTags,
@ -1517,8 +1517,8 @@ class FederationEventHandler:
)
async def backfill_event_id(
self, destination: str, room_id: str, event_id: str
) -> EventBase:
self, destinations: List[str], room_id: str, event_id: str
) -> PulledPduInfo:
"""Backfill a single event and persist it as a non-outlier which means
we also pull in all of the state and auth events necessary for it.
@ -1530,24 +1530,21 @@ class FederationEventHandler:
Raises:
FederationError if we are unable to find the event from the destination
"""
logger.info(
"backfill_event_id: event_id=%s from destination=%s", event_id, destination
)
logger.info("backfill_event_id: event_id=%s", event_id)
room_version = await self._store.get_room_version(room_id)
event_from_response = await self._federation_client.get_pdu(
[destination],
pulled_pdu_info = await self._federation_client.get_pdu(
destinations,
event_id,
room_version,
)
if not event_from_response:
if not pulled_pdu_info:
raise FederationError(
"ERROR",
404,
"Unable to find event_id=%s from destination=%s to backfill."
% (event_id, destination),
f"Unable to find event_id={event_id} from remote servers to backfill.",
affected=event_id,
)
@ -1555,13 +1552,13 @@ class FederationEventHandler:
# and auth events to de-outlier it. This also sets up the necessary
# `state_groups` for the event.
await self._process_pulled_events(
destination,
[event_from_response],
pulled_pdu_info.pull_origin,
[pulled_pdu_info.pdu],
# Prevent notifications going to clients
backfilled=True,
)
return event_from_response
return pulled_pdu_info
@trace
@tag_args
@ -1584,19 +1581,19 @@ class FederationEventHandler:
async def get_event(event_id: str) -> None:
with nested_logging_context(event_id):
try:
event = await self._federation_client.get_pdu(
pulled_pdu_info = await self._federation_client.get_pdu(
[destination],
event_id,
room_version,
)
if event is None:
if pulled_pdu_info is None:
logger.warning(
"Server %s didn't return event %s",
destination,
event_id,
)
return
events.append(event)
events.append(pulled_pdu_info.pdu)
except Exception as e:
logger.warning(

128
synapse/handlers/room.py
View File

@ -49,7 +49,6 @@ from synapse.api.constants import (
from synapse.api.errors import (
AuthError,
Codes,
HttpResponseException,
LimitExceededError,
NotFoundError,
StoreError,
@ -60,7 +59,6 @@ from synapse.api.room_versions import KNOWN_ROOM_VERSIONS, RoomVersion
from synapse.event_auth import validate_event_for_room_version
from synapse.events import EventBase
from synapse.events.utils import copy_and_fixup_power_levels_contents
from synapse.federation.federation_client import InvalidResponseError
from synapse.handlers.relations import BundledAggregations
from synapse.module_api import NOT_SPAM
from synapse.rest.admin._base import assert_user_is_admin
@ -1472,7 +1470,12 @@ class TimestampLookupHandler:
Raises:
SynapseError if unable to find any event locally in the given direction
"""
logger.debug(
"get_event_for_timestamp(room_id=%s, timestamp=%s, direction=%s) Finding closest event...",
room_id,
timestamp,
direction,
)
local_event_id = await self.store.get_event_id_for_timestamp(
room_id, timestamp, direction
)
@ -1524,85 +1527,54 @@ class TimestampLookupHandler:
)
)
# Loop through each homeserver candidate until we get a succesful response
for domain in likely_domains:
# We don't want to ask our own server for information we don't have
if domain == self.server_name:
continue
remote_response = await self.federation_client.timestamp_to_event(
destinations=likely_domains,
room_id=room_id,
timestamp=timestamp,
direction=direction,
)
if remote_response is not None:
logger.debug(
"get_event_for_timestamp: remote_response=%s",
remote_response,
)
try:
remote_response = await self.federation_client.timestamp_to_event(
domain, room_id, timestamp, direction
)
logger.debug(
"get_event_for_timestamp: response from domain(%s)=%s",
domain,
remote_response,
remote_event_id = remote_response.event_id
remote_origin_server_ts = remote_response.origin_server_ts
# Backfill this event so we can get a pagination token for
# it with `/context` and paginate `/messages` from this
# point.
pulled_pdu_info = await self.federation_event_handler.backfill_event_id(
likely_domains, room_id, remote_event_id
)
remote_event = pulled_pdu_info.pdu
# XXX: When we see that the remote server is not trustworthy,
# maybe we should not ask them first in the future.
if remote_origin_server_ts != remote_event.origin_server_ts:
logger.info(
"get_event_for_timestamp: Remote server (%s) claimed that remote_event_id=%s occured at remote_origin_server_ts=%s but that isn't true (actually occured at %s). Their claims are dubious and we should consider not trusting them.",
pulled_pdu_info.pull_origin,
remote_event_id,
remote_origin_server_ts,
remote_event.origin_server_ts,
)
remote_event_id = remote_response.event_id
remote_origin_server_ts = remote_response.origin_server_ts
# Backfill this event so we can get a pagination token for
# it with `/context` and paginate `/messages` from this
# point.
#
# TODO: The requested timestamp may lie in a part of the
# event graph that the remote server *also* didn't have,
# in which case they will have returned another event
# which may be nowhere near the requested timestamp. In
# the future, we may need to reconcile that gap and ask
# other homeservers, and/or extend `/timestamp_to_event`
# to return events on *both* sides of the timestamp to
# help reconcile the gap faster.
remote_event = (
await self.federation_event_handler.backfill_event_id(
domain, room_id, remote_event_id
)
)
# XXX: When we see that the remote server is not trustworthy,
# maybe we should not ask them first in the future.
if remote_origin_server_ts != remote_event.origin_server_ts:
logger.info(
"get_event_for_timestamp: Remote server (%s) claimed that remote_event_id=%s occured at remote_origin_server_ts=%s but that isn't true (actually occured at %s). Their claims are dubious and we should consider not trusting them.",
domain,
remote_event_id,
remote_origin_server_ts,
remote_event.origin_server_ts,
)
# Only return the remote event if it's closer than the local event
if not local_event or (
abs(remote_event.origin_server_ts - timestamp)
< abs(local_event.origin_server_ts - timestamp)
):
logger.info(
"get_event_for_timestamp: returning remote_event_id=%s (%s) since it's closer to timestamp=%s than local_event=%s (%s)",
remote_event_id,
remote_event.origin_server_ts,
timestamp,
local_event.event_id if local_event else None,
local_event.origin_server_ts if local_event else None,
)
return remote_event_id, remote_origin_server_ts
except (HttpResponseException, InvalidResponseError) as ex:
# Let's not put a high priority on some other homeserver
# failing to respond or giving a random response
logger.debug(
"get_event_for_timestamp: Failed to fetch /timestamp_to_event from %s because of exception(%s) %s args=%s",
domain,
type(ex).__name__,
ex,
ex.args,
)
except Exception:
# But we do want to see some exceptions in our code
logger.warning(
"get_event_for_timestamp: Failed to fetch /timestamp_to_event from %s because of exception",
domain,
exc_info=True,
# Only return the remote event if it's closer than the local event
if not local_event or (
abs(remote_event.origin_server_ts - timestamp)
< abs(local_event.origin_server_ts - timestamp)
):
logger.info(
"get_event_for_timestamp: returning remote_event_id=%s (%s) since it's closer to timestamp=%s than local_event=%s (%s)",
remote_event_id,
remote_event.origin_server_ts,
timestamp,
local_event.event_id if local_event else None,
local_event.origin_server_ts if local_event else None,
)
return remote_event_id, remote_origin_server_ts
# To appease mypy, we have to add both of these conditions to check for
# `None`. We only expect `local_event` to be `None` when

2
synapse/util/retryutils.py
View File

@ -51,7 +51,7 @@ class NotRetryingDestination(Exception):
destination: the domain in question
"""
msg = "Not retrying server %s." % (destination,)
msg = f"Not retrying server {destination} because we tried it recently retry_last_ts={retry_last_ts} and we won't check for another retry_interval={retry_interval}ms."
super().__init__(msg)
self.retry_last_ts = retry_last_ts

12
tests/federation/test_federation_client.py
View File

@ -142,14 +142,14 @@ class FederationClientTest(FederatingHomeserverTestCase):
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(
pulled_pdu_info = self.get_success(
self.hs.get_federation_client().get_pdu(
["yet.another.server"],
"event_should_not_exist",
RoomVersions.V9,
)
)
self.assertEqual(remote_pdu, None)
self.assertEqual(pulled_pdu_info, None)
def test_get_pdu(self):
"""Test to make sure an event is returned by `get_pdu()`"""
@ -169,13 +169,15 @@ class FederationClientTest(FederatingHomeserverTestCase):
remote_pdu.internal_metadata.outlier = True
# Get the event again. This time it should read it from cache.
remote_pdu2 = self.get_success(
pulled_pdu_info2 = self.get_success(
self.hs.get_federation_client().get_pdu(
["yet.another.server"],
remote_pdu.event_id,
RoomVersions.V9,
)
)
self.assertIsNotNone(pulled_pdu_info2)
remote_pdu2 = pulled_pdu_info2.pdu
# Sanity check that we are working against the same event
self.assertEqual(remote_pdu.event_id, remote_pdu2.event_id)
@ -215,13 +217,15 @@ class FederationClientTest(FederatingHomeserverTestCase):
)
)
remote_pdu = self.get_success(
pulled_pdu_info = self.get_success(
self.hs.get_federation_client().get_pdu(
["yet.another.server"],
"event_id",
RoomVersions.V9,
)
)
self.assertIsNotNone(pulled_pdu_info)
remote_pdu = pulled_pdu_info.pdu
# check the right call got made to the agent
self._mock_agent.request.assert_called_once_with(