m.room.aliases events do not necessarily correspond to room directory entries #533
Description
the content of an m.room.aliases event is best treated as a guide, at best. There are several reasons for this:
- There is nothing stopping a malicious or buggy homeserver from claiming that a given alias points to one room in an
m.room.aliasesevent, but then responding differently in a directory lookup.- In any case, it is inherently racy.
On the subject of buggy homeservers: Deleting an alias via DELETE /directory/room doesn't seem to delete it from m.room.aliases (SYN-598) synapse#1477- There is nothing stopping a homeserver advertising aliases on another server: m.room.aliases may contain aliases from other homeservers #539
- The alias might belong to a homeserver which is no longer participating in the room, and which has since updated the alias to point elsewhere. The federation protocol does not allow departed homeservers to send events to a room, so there is no way for it to update the room state.