We're in the middle of properly mitigating spam caused by malicious aliases being added to a room. However, until this work fully lands, we temporarily filter out all m.room.aliases events from /sync and /messages on the CS API, to remove abusive aliases. This is considered acceptable as m.room.aliases events were never a reliable record of the given alias->id mapping and were purely informational, and in their current state do more harm than good.
Purge jobs don't delete the latest event in a room in order to keep the forward extremity and not break the room. On the other hand, get_state_events, when given an at_token argument calls filter_events_for_client to know if the user can see the event that matches that (sync) token. That function uses the retention policies of the events it's given to filter out those that are too old from a client's view.
Some clients, such as Riot, when loading a room, request the list of members for the latest sync token it knows about, and get confused to the point of refusing to send any message if the server tells it that it can't get that information. This can happen very easily with the message retention feature turned on and a room with low activity so that the last event sent becomes too old according to the room's retention policy.
An easy and clean fix for that issue is to discard the room's retention policies when retrieving state.
When filtering events to send to server we check more than just history
visibility. However when deciding whether to backfill or not we only
care about the history visibility.
Currently when fetching state groups from the data store we make two
hits two the database: once for members and once for non-members (unless
request is filtered to one or the other). This adds needless load to the
datbase, so this PR refactors the lookup to make only a single database
hit.
We're better off hashing just the event_id than the whole ((type, state_key),
event_id) tuple - so use a dict instead of a set.
Also, iteritems > items.
This is only used by filter_events_for_client, so we can simplify the whole
thing by just doing one user at a time, and removing a dead storage function to
boot.
