Add MSC3030 experimental client and federation API endpoints to get the closest event to a given timestamp (#9445)

MSC3030: https://github.com/matrix-org/matrix-doc/pull/3030

Client API endpoint. This will also go and fetch from the federation API endpoint if unable to find an event locally or we found an extremity with possibly a closer event we don't know about.
```
GET /_matrix/client/unstable/org.matrix.msc3030/rooms/<roomID>/timestamp_to_event?ts=<timestamp>&dir=<direction>
{
    "event_id": ...
    "origin_server_ts": ...
}
```

Federation API endpoint:
```
GET /_matrix/federation/unstable/org.matrix.msc3030/timestamp_to_event/<roomID>?ts=<timestamp>&dir=<direction>
{
    "event_id": ...
    "origin_server_ts": ...
}
```

Co-authored-by: Erik Johnston <erik@matrix.org>
This commit is contained in:
Eric Eastwood 2021-12-02 01:02:20 -06:00 committed by GitHub
parent 84dc50e160
commit a6f1a3abec
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13 changed files with 674 additions and 31 deletions

1
changelog.d/9445.feature Normal file
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@ -0,0 +1 @@
Add [MSC3030](https://github.com/matrix-org/matrix-doc/pull/3030) experimental client and federation API endpoints to get the closest event to a given timestamp.

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@ -46,3 +46,6 @@ class ExperimentalConfig(Config):
# MSC3266 (room summary api)
self.msc3266_enabled: bool = experimental.get("msc3266_enabled", False)
# MSC3030 (Jump to date API endpoint)
self.msc3030_enabled: bool = experimental.get("msc3030_enabled", False)

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@ -1517,6 +1517,83 @@ class FederationClient(FederationBase):
self._get_room_hierarchy_cache[(room_id, suggested_only)] = result
return result
async def timestamp_to_event(
self, destination: str, room_id: str, timestamp: int, direction: str
) -> "TimestampToEventResponse":
"""
Calls a remote federating server at `destination` asking for their
closest event to the given timestamp in the given direction. Also
validates the response to always return the expected keys or raises an
error.
Args:
destination: Domain name of the remote homeserver
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
Raises:
Various exceptions when the request fails
InvalidResponseError when the response does not have the correct
keys or wrong types
"""
remote_response = await self.transport_layer.timestamp_to_event(
destination, room_id, timestamp, direction
)
if not isinstance(remote_response, dict):
raise InvalidResponseError(
"Response must be a JSON dictionary but received %r" % remote_response
)
try:
return TimestampToEventResponse.from_json_dict(remote_response)
except ValueError as e:
raise InvalidResponseError(str(e))
@attr.s(frozen=True, slots=True, auto_attribs=True)
class TimestampToEventResponse:
"""Typed response dictionary for the federation /timestamp_to_event endpoint"""
event_id: str
origin_server_ts: int
# the raw data, including the above keys
data: JsonDict
@classmethod
def from_json_dict(cls, d: JsonDict) -> "TimestampToEventResponse":
"""Parsed response from the federation /timestamp_to_event endpoint
Args:
d: JSON object response to be parsed
Raises:
ValueError if d does not the correct keys or they are the wrong types
"""
event_id = d.get("event_id")
if not isinstance(event_id, str):
raise ValueError(
"Invalid response: 'event_id' must be a str but received %r" % event_id
)
origin_server_ts = d.get("origin_server_ts")
if not isinstance(origin_server_ts, int):
raise ValueError(
"Invalid response: 'origin_server_ts' must be a int but received %r"
% origin_server_ts
)
return cls(event_id, origin_server_ts, d)
@attr.s(frozen=True, slots=True, auto_attribs=True)
class FederationSpaceSummaryEventResult:

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@ -110,6 +110,7 @@ class FederationServer(FederationBase):
super().__init__(hs)
self.handler = hs.get_federation_handler()
self.storage = hs.get_storage()
self._federation_event_handler = hs.get_federation_event_handler()
self.state = hs.get_state_handler()
self._event_auth_handler = hs.get_event_auth_handler()
@ -200,6 +201,48 @@ class FederationServer(FederationBase):
return 200, res
async def on_timestamp_to_event_request(
self, origin: str, room_id: str, timestamp: int, direction: str
) -> Tuple[int, Dict[str, Any]]:
"""When we receive a federated `/timestamp_to_event` request,
handle all of the logic for validating and fetching the event.
Args:
origin: The server we received the event 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:
Tuple indicating the response status code and dictionary response
body including `event_id`.
"""
with (await self._server_linearizer.queue((origin, room_id))):
origin_host, _ = parse_server_name(origin)
await self.check_server_matches_acl(origin_host, room_id)
# We only try to fetch data from the local database
event_id = await self.store.get_event_id_for_timestamp(
room_id, timestamp, direction
)
if event_id:
event = await self.store.get_event(
event_id, allow_none=False, allow_rejected=False
)
return 200, {
"event_id": event_id,
"origin_server_ts": event.origin_server_ts,
}
raise SynapseError(
404,
"Unable to find event from %s in direction %s" % (timestamp, direction),
errcode=Codes.NOT_FOUND,
)
async def on_incoming_transaction(
self,
origin: str,

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@ -148,6 +148,42 @@ class TransportLayerClient:
destination, path=path, args=args, try_trailing_slash_on_400=True
)
@log_function
async def timestamp_to_event(
self, destination: str, room_id: str, timestamp: int, direction: str
) -> Union[JsonDict, List]:
"""
Calls a remote federating server at `destination` asking for their
closest event to the given timestamp in the given direction.
Args:
destination: Domain name of the remote homeserver
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:
Response dict received from the remote homeserver.
Raises:
Various exceptions when the request fails
"""
path = _create_path(
FEDERATION_UNSTABLE_PREFIX,
"/org.matrix.msc3030/timestamp_to_event/%s",
room_id,
)
args = {"ts": [str(timestamp)], "dir": [direction]}
remote_response = await self.client.get_json(
destination, path=path, args=args, try_trailing_slash_on_400=True
)
return remote_response
@log_function
async def send_transaction(
self,

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@ -22,7 +22,10 @@ from synapse.federation.transport.server._base import (
Authenticator,
BaseFederationServlet,
)
from synapse.federation.transport.server.federation import FEDERATION_SERVLET_CLASSES
from synapse.federation.transport.server.federation import (
FEDERATION_SERVLET_CLASSES,
FederationTimestampLookupServlet,
)
from synapse.federation.transport.server.groups_local import GROUP_LOCAL_SERVLET_CLASSES
from synapse.federation.transport.server.groups_server import (
GROUP_SERVER_SERVLET_CLASSES,
@ -324,6 +327,13 @@ def register_servlets(
)
for servletclass in DEFAULT_SERVLET_GROUPS[servlet_group]:
# Only allow the `/timestamp_to_event` servlet if msc3030 is enabled
if (
servletclass == FederationTimestampLookupServlet
and not hs.config.experimental.msc3030_enabled
):
continue
servletclass(
hs=hs,
authenticator=authenticator,

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@ -174,6 +174,46 @@ class FederationBackfillServlet(BaseFederationServerServlet):
return await self.handler.on_backfill_request(origin, room_id, versions, limit)
class FederationTimestampLookupServlet(BaseFederationServerServlet):
"""
API endpoint to fetch the `event_id` of the closest event to the given
timestamp (`ts` query parameter) in the given direction (`dir` query
parameter).
Useful for other homeservers when they're unable to find an event locally.
`ts` is a timestamp in milliseconds where we will find the closest event in
the given direction.
`dir` can be `f` or `b` to indicate forwards and backwards in time from the
given timestamp.
GET /_matrix/federation/unstable/org.matrix.msc3030/timestamp_to_event/<roomID>?ts=<timestamp>&dir=<direction>
{
"event_id": ...
}
"""
PATH = "/timestamp_to_event/(?P<room_id>[^/]*)/?"
PREFIX = FEDERATION_UNSTABLE_PREFIX + "/org.matrix.msc3030"
async def on_GET(
self,
origin: str,
content: Literal[None],
query: Dict[bytes, List[bytes]],
room_id: str,
) -> Tuple[int, JsonDict]:
timestamp = parse_integer_from_args(query, "ts", required=True)
direction = parse_string_from_args(
query, "dir", default="f", allowed_values=["f", "b"], required=True
)
return await self.handler.on_timestamp_to_event_request(
origin, room_id, timestamp, direction
)
class FederationQueryServlet(BaseFederationServerServlet):
PATH = "/query/(?P<query_type>[^/]*)"
@ -683,6 +723,7 @@ FEDERATION_SERVLET_CLASSES: Tuple[Type[BaseFederationServlet], ...] = (
FederationStateV1Servlet,
FederationStateIdsServlet,
FederationBackfillServlet,
FederationTimestampLookupServlet,
FederationQueryServlet,
FederationMakeJoinServlet,
FederationMakeLeaveServlet,

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@ -68,6 +68,37 @@ if TYPE_CHECKING:
logger = logging.getLogger(__name__)
def get_domains_from_state(state: StateMap[EventBase]) -> List[Tuple[str, int]]:
"""Get joined domains from state
Args:
state: State map from type/state key to event.
Returns:
Returns a list of servers with the lowest depth of their joins.
Sorted by lowest depth first.
"""
joined_users = [
(state_key, int(event.depth))
for (e_type, state_key), event in state.items()
if e_type == EventTypes.Member and event.membership == Membership.JOIN
]
joined_domains: Dict[str, int] = {}
for u, d in joined_users:
try:
dom = get_domain_from_id(u)
old_d = joined_domains.get(dom)
if old_d:
joined_domains[dom] = min(d, old_d)
else:
joined_domains[dom] = d
except Exception:
pass
return sorted(joined_domains.items(), key=lambda d: d[1])
class FederationHandler:
"""Handles general incoming federation requests
@ -268,36 +299,6 @@ class FederationHandler:
curr_state = await self.state_handler.get_current_state(room_id)
def get_domains_from_state(state: StateMap[EventBase]) -> List[Tuple[str, int]]:
"""Get joined domains from state
Args:
state: State map from type/state key to event.
Returns:
Returns a list of servers with the lowest depth of their joins.
Sorted by lowest depth first.
"""
joined_users = [
(state_key, int(event.depth))
for (e_type, state_key), event in state.items()
if e_type == EventTypes.Member and event.membership == Membership.JOIN
]
joined_domains: Dict[str, int] = {}
for u, d in joined_users:
try:
dom = get_domain_from_id(u)
old_d = joined_domains.get(dom)
if old_d:
joined_domains[dom] = min(d, old_d)
else:
joined_domains[dom] = d
except Exception:
pass
return sorted(joined_domains.items(), key=lambda d: d[1])
curr_domains = get_domains_from_state(curr_state)
likely_domains = [

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@ -46,6 +46,7 @@ from synapse.api.constants import (
from synapse.api.errors import (
AuthError,
Codes,
HttpResponseException,
LimitExceededError,
NotFoundError,
StoreError,
@ -56,6 +57,8 @@ 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_power_levels_contents
from synapse.federation.federation_client import InvalidResponseError
from synapse.handlers.federation import get_domains_from_state
from synapse.rest.admin._base import assert_user_is_admin
from synapse.storage.state import StateFilter
from synapse.streams import EventSource
@ -1220,6 +1223,147 @@ class RoomContextHandler:
return results
class TimestampLookupHandler:
def __init__(self, hs: "HomeServer"):
self.server_name = hs.hostname
self.store = hs.get_datastore()
self.state_handler = hs.get_state_handler()
self.federation_client = hs.get_federation_client()
async def get_event_for_timestamp(
self,
requester: Requester,
room_id: str,
timestamp: int,
direction: str,
) -> Tuple[str, int]:
"""Find the closest event to the given timestamp in the given direction.
If we can't find an event locally or the event we have locally is next to a gap,
it will ask other federated homeservers for an event.
Args:
requester: The user making the request according to the access token
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 tuple containing the `event_id` closest to the given timestamp in
the given direction and the `origin_server_ts`.
Raises:
SynapseError if unable to find any event locally in the given direction
"""
local_event_id = await self.store.get_event_id_for_timestamp(
room_id, timestamp, direction
)
logger.debug(
"get_event_for_timestamp: locally, we found event_id=%s closest to timestamp=%s",
local_event_id,
timestamp,
)
# Check for gaps in the history where events could be hiding in between
# the timestamp given and the event we were able to find locally
is_event_next_to_backward_gap = False
is_event_next_to_forward_gap = False
if local_event_id:
local_event = await self.store.get_event(
local_event_id, allow_none=False, allow_rejected=False
)
if direction == "f":
# We only need to check for a backward gap if we're looking forwards
# to ensure there is nothing in between.
is_event_next_to_backward_gap = (
await self.store.is_event_next_to_backward_gap(local_event)
)
elif direction == "b":
# We only need to check for a forward gap if we're looking backwards
# to ensure there is nothing in between
is_event_next_to_forward_gap = (
await self.store.is_event_next_to_forward_gap(local_event)
)
# If we found a gap, we should probably ask another homeserver first
# about more history in between
if (
not local_event_id
or is_event_next_to_backward_gap
or is_event_next_to_forward_gap
):
logger.debug(
"get_event_for_timestamp: locally, we found event_id=%s closest to timestamp=%s which is next to a gap in event history so we're asking other homeservers first",
local_event_id,
timestamp,
)
# Find other homeservers from the given state in the room
curr_state = await self.state_handler.get_current_state(room_id)
curr_domains = get_domains_from_state(curr_state)
likely_domains = [
domain for domain, depth in curr_domains if domain != self.server_name
]
# Loop through each homeserver candidate until we get a succesful response
for domain in likely_domains:
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,
)
# TODO: Do we want to persist this as an extremity?
# TODO: I think ideally, we would try to backfill from
# this event and run this whole
# `get_event_for_timestamp` function again to make sure
# they didn't give us an event from their gappy history.
remote_event_id = remote_response.event_id
origin_server_ts = remote_response.origin_server_ts
# Only return the remote event if it's closer than the local event
if not local_event or (
abs(origin_server_ts - timestamp)
< abs(local_event.origin_server_ts - timestamp)
):
return remote_event_id, 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(
"Failed to fetch /timestamp_to_event from %s because of exception(%s) %s args=%s",
domain,
type(ex).__name__,
ex,
ex.args,
)
except Exception as ex:
# But we do want to see some exceptions in our code
logger.warning(
"Failed to fetch /timestamp_to_event from %s because of exception(%s) %s args=%s",
domain,
type(ex).__name__,
ex,
ex.args,
)
if not local_event_id:
raise SynapseError(
404,
"Unable to find event from %s in direction %s" % (timestamp, direction),
errcode=Codes.NOT_FOUND,
)
return local_event_id, local_event.origin_server_ts
class RoomEventSource(EventSource[RoomStreamToken, EventBase]):
def __init__(self, hs: "HomeServer"):
self.store = hs.get_datastore()

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@ -79,6 +79,35 @@ def parse_integer(
return parse_integer_from_args(args, name, default, required)
@overload
def parse_integer_from_args(
args: Mapping[bytes, Sequence[bytes]],
name: str,
default: Optional[int] = None,
) -> Optional[int]:
...
@overload
def parse_integer_from_args(
args: Mapping[bytes, Sequence[bytes]],
name: str,
*,
required: Literal[True],
) -> int:
...
@overload
def parse_integer_from_args(
args: Mapping[bytes, Sequence[bytes]],
name: str,
default: Optional[int] = None,
required: bool = False,
) -> Optional[int]:
...
def parse_integer_from_args(
args: Mapping[bytes, Sequence[bytes]],
name: str,

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@ -1070,6 +1070,62 @@ def register_txn_path(
)
class TimestampLookupRestServlet(RestServlet):
"""
API endpoint to fetch the `event_id` of the closest event to the given
timestamp (`ts` query parameter) in the given direction (`dir` query
parameter).
Useful for cases like jump to date so you can start paginating messages from
a given date in the archive.
`ts` is a timestamp in milliseconds where we will find the closest event in
the given direction.
`dir` can be `f` or `b` to indicate forwards and backwards in time from the
given timestamp.
GET /_matrix/client/unstable/org.matrix.msc3030/rooms/<roomID>/timestamp_to_event?ts=<timestamp>&dir=<direction>
{
"event_id": ...
}
"""
PATTERNS = (
re.compile(
"^/_matrix/client/unstable/org.matrix.msc3030"
"/rooms/(?P<room_id>[^/]*)/timestamp_to_event$"
),
)
def __init__(self, hs: "HomeServer"):
super().__init__()
self._auth = hs.get_auth()
self._store = hs.get_datastore()
self.timestamp_lookup_handler = hs.get_timestamp_lookup_handler()
async def on_GET(
self, request: SynapseRequest, room_id: str
) -> Tuple[int, JsonDict]:
requester = await self._auth.get_user_by_req(request)
await self._auth.check_user_in_room(room_id, requester.user.to_string())
timestamp = parse_integer(request, "ts", required=True)
direction = parse_string(request, "dir", default="f", allowed_values=["f", "b"])
(
event_id,
origin_server_ts,
) = await self.timestamp_lookup_handler.get_event_for_timestamp(
requester, room_id, timestamp, direction
)
return 200, {
"event_id": event_id,
"origin_server_ts": origin_server_ts,
}
class RoomSpaceSummaryRestServlet(RestServlet):
PATTERNS = (
re.compile(
@ -1239,6 +1295,8 @@ def register_servlets(
RoomAliasListServlet(hs).register(http_server)
SearchRestServlet(hs).register(http_server)
RoomCreateRestServlet(hs).register(http_server)
if hs.config.experimental.msc3030_enabled:
TimestampLookupRestServlet(hs).register(http_server)
# Some servlets only get registered for the main process.
if not is_worker:

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@ -97,6 +97,7 @@ from synapse.handlers.room import (
RoomContextHandler,
RoomCreationHandler,
RoomShutdownHandler,
TimestampLookupHandler,
)
from synapse.handlers.room_batch import RoomBatchHandler
from synapse.handlers.room_list import RoomListHandler
@ -728,6 +729,10 @@ class HomeServer(metaclass=abc.ABCMeta):
def get_room_context_handler(self) -> RoomContextHandler:
return RoomContextHandler(self)
@cache_in_self
def get_timestamp_lookup_handler(self) -> TimestampLookupHandler:
return TimestampLookupHandler(self)
@cache_in_self
def get_registration_handler(self) -> RegistrationHandler:
return RegistrationHandler(self)

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@ -1762,3 +1762,198 @@ class EventsWorkerStore(SQLBaseStore):
"_cleanup_old_transaction_ids",
_cleanup_old_transaction_ids_txn,
)
async def is_event_next_to_backward_gap(self, event: EventBase) -> bool:
"""Check if the given event is next to a backward gap of missing events.
<latest messages> A(False)--->B(False)--->C(True)---> <gap, unknown events> <oldest messages>
Args:
room_id: room where the event lives
event_id: event to check
Returns:
Boolean indicating whether it's an extremity
"""
def is_event_next_to_backward_gap_txn(txn: LoggingTransaction) -> bool:
# If the event in question has any of its prev_events listed as a
# backward extremity, it's next to a gap.
#
# We can't just check the backward edges in `event_edges` because
# when we persist events, we will also record the prev_events as
# edges to the event in question regardless of whether we have those
# prev_events yet. We need to check whether those prev_events are
# backward extremities, also known as gaps, that need to be
# backfilled.
backward_extremity_query = """
SELECT 1 FROM event_backward_extremities
WHERE
room_id = ?
AND %s
LIMIT 1
"""
# If the event in question is a backward extremity or has any of its
# prev_events listed as a backward extremity, it's next to a
# backward gap.
clause, args = make_in_list_sql_clause(
self.database_engine,
"event_id",
[event.event_id] + list(event.prev_event_ids()),
)
txn.execute(backward_extremity_query % (clause,), [event.room_id] + args)
backward_extremities = txn.fetchall()
# We consider any backward extremity as a backward gap
if len(backward_extremities):
return True
return False
return await self.db_pool.runInteraction(
"is_event_next_to_backward_gap_txn",
is_event_next_to_backward_gap_txn,
)
async def is_event_next_to_forward_gap(self, event: EventBase) -> bool:
"""Check if the given event is next to a forward gap of missing events.
The gap in front of the latest events is not considered a gap.
<latest messages> A(False)--->B(False)--->C(False)---> <gap, unknown events> <oldest messages>
<latest messages> A(False)--->B(False)---> <gap, unknown events> --->D(True)--->E(False) <oldest messages>
Args:
room_id: room where the event lives
event_id: event to check
Returns:
Boolean indicating whether it's an extremity
"""
def is_event_next_to_gap_txn(txn: LoggingTransaction) -> bool:
# If the event in question is a forward extremity, we will just
# consider any potential forward gap as not a gap since it's one of
# the latest events in the room.
#
# `event_forward_extremities` does not include backfilled or outlier
# events so we can't rely on it to find forward gaps. We can only
# use it to determine whether a message is the latest in the room.
#
# We can't combine this query with the `forward_edge_query` below
# because if the event in question has no forward edges (isn't
# referenced by any other event's prev_events) but is in
# `event_forward_extremities`, we don't want to return 0 rows and
# say it's next to a gap.
forward_extremity_query = """
SELECT 1 FROM event_forward_extremities
WHERE
room_id = ?
AND event_id = ?
LIMIT 1
"""
# Check to see whether the event in question is already referenced
# by another event. If we don't see any edges, we're next to a
# forward gap.
forward_edge_query = """
SELECT 1 FROM event_edges
/* Check to make sure the event referencing our event in question is not rejected */
LEFT JOIN rejections ON event_edges.event_id == rejections.event_id
WHERE
event_edges.room_id = ?
AND event_edges.prev_event_id = ?
/* It's not a valid edge if the event referencing our event in
* question is rejected.
*/
AND rejections.event_id IS NULL
LIMIT 1
"""
# We consider any forward extremity as the latest in the room and
# not a forward gap.
#
# To expand, even though there is technically a gap at the front of
# the room where the forward extremities are, we consider those the
# latest messages in the room so asking other homeservers for more
# is useless. The new latest messages will just be federated as
# usual.
txn.execute(forward_extremity_query, (event.room_id, event.event_id))
forward_extremities = txn.fetchall()
if len(forward_extremities):
return False
# If there are no forward edges to the event in question (another
# event hasn't referenced this event in their prev_events), then we
# assume there is a forward gap in the history.
txn.execute(forward_edge_query, (event.room_id, event.event_id))
forward_edges = txn.fetchall()
if not len(forward_edges):
return True
return False
return await self.db_pool.runInteraction(
"is_event_next_to_gap_txn",
is_event_next_to_gap_txn,
)
async def get_event_id_for_timestamp(
self, room_id: str, timestamp: int, direction: str
) -> Optional[str]:
"""Find the closest event to the given timestamp in the given direction.
Args:
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:
The closest event_id otherwise None if we can't find any event in
the given direction.
"""
sql_template = """
SELECT event_id FROM events
LEFT JOIN rejections USING (event_id)
WHERE
origin_server_ts %s ?
AND room_id = ?
/* Make sure event is not rejected */
AND rejections.event_id IS NULL
ORDER BY origin_server_ts %s
LIMIT 1;
"""
def get_event_id_for_timestamp_txn(txn: LoggingTransaction) -> Optional[str]:
if direction == "b":
# Find closest event *before* a given timestamp. We use descending
# (which gives values largest to smallest) because we want the
# largest possible timestamp *before* the given timestamp.
comparison_operator = "<="
order = "DESC"
else:
# Find closest event *after* a given timestamp. We use ascending
# (which gives values smallest to largest) because we want the
# closest possible timestamp *after* the given timestamp.
comparison_operator = ">="
order = "ASC"
txn.execute(
sql_template % (comparison_operator, order), (timestamp, room_id)
)
row = txn.fetchone()
if row:
(event_id,) = row
return event_id
return None
if direction not in ("f", "b"):
raise ValueError("Unknown direction: %s" % (direction,))
return await self.db_pool.runInteraction(
"get_event_id_for_timestamp_txn",
get_event_id_for_timestamp_txn,
)