Rooms::DirectsController relaxes ensure_can_administer to true, because every
participant in a direct room may administer it. set_room was inherited unscoped,
though, so that relaxation applied to any room the caller was merely a member of:
DELETE /rooms/directs/<id> destroyed open and closed rooms and all their messages.
The same unscoped lookup let a direct room be loaded by the opens and closeds
controllers, where force_room_type promoted it. Promoting a DM to open grants every
user on the account membership and republishes the whole conversation, including the
other participant's messages; converting it to closed lets the initiator revise who
is in it and lock the other participant out.
Each controller now narrows room_scope to the types it may act on. Opens and closeds
keep reach into each other, since converting between them is a feature. Neither can
reach a direct room, and directs can only reach directs.
Room also refuses to change type away from Rooms::Direct, so the invariant holds for
any future caller of becomes! rather than only these two controllers.
Jeremy Daer
David Heinemeier Hansson
Kevin McConnell