diff --git a/synapse/events/builder.py b/synapse/events/builder.py
index 10ef01131b..76df083d69 100644
--- a/synapse/events/builder.py
+++ b/synapse/events/builder.py
@@ -24,7 +24,7 @@ from typing import TYPE_CHECKING, Any, Dict, List, Optional, Tuple, Union
import attr
from signedjson.types import SigningKey
-from synapse.api.constants import MAX_DEPTH
+from synapse.api.constants import MAX_DEPTH, EventTypes
from synapse.api.room_versions import (
KNOWN_EVENT_FORMAT_VERSIONS,
EventFormatVersions,
@@ -109,6 +109,19 @@ class EventBuilder:
def is_state(self) -> bool:
return self._state_key is not None
+ def is_mine_id(self, user_id: str) -> bool:
+ """Determines whether a user ID or room alias originates from this homeserver.
+
+ Returns:
+ `True` if the hostname part of the user ID or room alias matches this
+ homeserver.
+ `False` otherwise, or if the user ID or room alias is malformed.
+ """
+ localpart_hostname = user_id.split(":", 1)
+ if len(localpart_hostname) < 2:
+ return False
+ return localpart_hostname[1] == self._hostname
+
async def build(
self,
prev_event_ids: List[str],
@@ -142,6 +155,46 @@ class EventBuilder:
self, state_ids
)
+ # Check for out-of-band membership that may have been exposed on `/sync` but
+ # the events have not been de-outliered yet so they won't be part of the
+ # room state yet.
+ #
+ # This helps in situations where a remote homeserver invites a local user to
+ # a room that we're already participating in; and we've persisted the invite
+ # as an out-of-band membership (outlier), but it hasn't been pushed to us as
+ # part of a `/send` transaction yet and de-outliered. This also helps for
+ # any of the other out-of-band membership transitions.
+ #
+ # As an optimization, we could check if the room state already includes a
+ # non-`leave` membership event, then we can assume the membership event has
+ # been de-outliered and we don't need to check for an out-of-band
+ # membership. But we don't have the necessary information from a
+ # `StateMap[str]` and we'll just have to take the hit of this extra lookup
+ # for any membership event for now.
+ if self.type == EventTypes.Member and self.is_mine_id(self.state_key):
+ (
+ _membership,
+ member_event_id,
+ ) = await self._store.get_local_current_membership_for_user_in_room(
+ user_id=self.state_key,
+ room_id=self.room_id,
+ )
+ # There is no need to check if the membership is actually an
+ # out-of-band membership (`outlier`) as we would end up with the
+ # same result either way (adding the member event to the
+ # `auth_event_ids`).
+ if (
+ member_event_id is not None
+ # We only need to be careful about duplicating the event in the
+ # `auth_event_ids` list (duplicate `type`/`state_key` is part of the
+ # authorization rules)
+ and member_event_id not in auth_event_ids
+ ):
+ auth_event_ids.append(member_event_id)
+ # Also make sure to point to the previous membership event that will
+ # allow this one to happen so the computed state works out.
+ prev_event_ids.append(member_event_id)
+
format_version = self.room_version.event_format
# The types of auth/prev events changes between event versions.
prev_events: Union[StrCollection, List[Tuple[str, Dict[str, str]]]]
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