Discard retention policies when retrieving state

changelog.d/6436.bugfix

@@ -0,0 +1 @@
+Fix a bug where a room could become unusable with a low retention policy and a low activity.

synapse/handlers/message.py

@@ -138,7 +138,7 @@ def get_state_events(
  raise NotFoundError("Can't find event for token %s" % (at_token,))
 
  visible_events = yield filter_events_for_client(
- self.storage, user_id, last_events
+ self.storage, user_id, last_events, apply_retention_policies=False
  )
 
  event = last_events[0]

synapse/visibility.py

@@ -44,7 +44,12 @@
 
 @defer.inlineCallbacks
 def filter_events_for_client(
- storage: Storage, user_id, events, is_peeking=False, always_include_ids=frozenset()
+ storage: Storage,
+ user_id,
+ events,
+ is_peeking=False,
+ always_include_ids=frozenset(),
+ apply_retention_policies=True,
 ):
  """
  Check which events a user is allowed to see
@@ -59,6 +64,10 @@ def filter_events_for_client(
  events
  always_include_ids (set(event_id)): set of event ids to specifically
  include (unless sender is ignored)
+ apply_retention_policies (bool): Whether to filter out events that's older than
+ allowed by the room's retention policy. Useful when this function is called
+ to e.g. check whether a user should be allowed to see the state at a given
+ event rather than to know if it should send an event to a user's client(s).
 
  Returns:
  Deferred[list[synapse.events.EventBase]]
@@ -86,13 +95,14 @@ def filter_events_for_client(
 
  erased_senders = yield storage.main.are_users_erased((e.sender for e in events))
 
- room_ids = set(e.room_id for e in events)
- retention_policies = {}
+ if apply_retention_policies:
+ room_ids = set(e.room_id for e in events)
+ retention_policies = {}
 
- for room_id in room_ids:
- retention_policies[room_id] = yield storage.main.get_retention_policy_for_room(
- room_id
- )
+  for room_id in room_ids:
+  retention_policies[
+  room_id
+  ] = yield storage.main.get_retention_policy_for_room(room_id)
 
  def allowed(event):
  """
@@ -113,7 +123,7 @@ def allowed(event):
 
  # Don't try to apply the room's retention policy if the event is a state event, as
  # MSC1763 states that retention is only considered for non-state events.
- if not event.is_state():
+ if apply_retention_policies and not event.is_state():
  retention_policy = retention_policies[event.room_id]
  max_lifetime = retention_policy.get("max_lifetime")