Sort child events according to MSC1772 for the spaces summary API. (#9954)

This should help ensure that equivalent results are achieved between
homeservers querying for the summary of a space.

This implements modified MSC1772 rules, according to MSC2946.
The different is that the origin_server_ts of the m.room.create event
is not used as a tie-breaker since this might not be known if the
homeserver is not part of the room.
This commit is contained in:
Patrick Cloke 2021-05-11 12:57:39 -04:00 committed by GitHub
parent f4833e0c06
commit 27c375f812
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3 changed files with 151 additions and 2 deletions

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@ -14,6 +14,7 @@
import itertools
import logging
import re
from collections import deque
from typing import TYPE_CHECKING, Iterable, List, Optional, Sequence, Set, Tuple, cast
@ -226,6 +227,23 @@ class SpaceSummaryHandler:
suggested_only: bool,
max_children: Optional[int],
) -> Tuple[Sequence[JsonDict], Sequence[JsonDict]]:
"""
Generate a room entry and a list of event entries for a given room.
Args:
requester: The requesting user, or None if this is over federation.
room_id: The room ID to summarize.
suggested_only: True if only suggested children should be returned.
Otherwise, all children are returned.
max_children: The maximum number of children to return for this node.
Returns:
A tuple of:
An iterable of a single value of the room.
An iterable of the sorted children events. This may be limited
to a maximum size or may include all children.
"""
if not await self._is_room_accessible(room_id, requester):
return (), ()
@ -357,6 +375,18 @@ class SpaceSummaryHandler:
return room_entry
async def _get_child_events(self, room_id: str) -> Iterable[EventBase]:
"""
Get the child events for a given room.
The returned results are sorted for stability.
Args:
room_id: The room id to get the children of.
Returns:
An iterable of sorted child events.
"""
# look for child rooms/spaces.
current_state_ids = await self._store.get_current_state_ids(room_id)
@ -370,8 +400,9 @@ class SpaceSummaryHandler:
]
)
# filter out any events without a "via" (which implies it has been redacted)
return (e for e in events if _has_valid_via(e))
# filter out any events without a "via" (which implies it has been redacted),
# and order to ensure we return stable results.
return sorted(filter(_has_valid_via, events), key=_child_events_comparison_key)
@attr.s(frozen=True, slots=True)
@ -397,3 +428,39 @@ def _is_suggested_child_event(edge_event: EventBase) -> bool:
return True
logger.debug("Ignorning not-suggested child %s", edge_event.state_key)
return False
# Order may only contain characters in the range of \x20 (space) to \x7F (~).
_INVALID_ORDER_CHARS_RE = re.compile(r"[^\x20-\x7F]")
def _child_events_comparison_key(child: EventBase) -> Tuple[bool, Optional[str], str]:
"""
Generate a value for comparing two child events for ordering.
The rules for ordering are supposed to be:
1. The 'order' key, if it is valid.
2. The 'origin_server_ts' of the 'm.room.create' event.
3. The 'room_id'.
But we skip step 2 since we may not have any state from the room.
Args:
child: The event for generating a comparison key.
Returns:
The comparison key as a tuple of:
False if the ordering is valid.
The ordering field.
The room ID.
"""
order = child.content.get("order")
# If order is not a string or doesn't meet the requirements, ignore it.
if not isinstance(order, str):
order = None
elif len(order) > 50 or _INVALID_ORDER_CHARS_RE.search(order):
order = None
# Items without an order come last.
return (order is None, order, child.room_id)