4267-auto-forget.md

MSC4267: Automatically forgetting rooms on leave

Matrix discriminates between "leaving" and "forgetting" a room. /_matrix/client/v3/rooms/{roomId}/leave stops a user participating in a room but still allows them to retrieve history. A subsequent call to /_matrix/client/v3/rooms/{roomId}/forget then stops the user from being able to retrieve history.

Clients don't always differentiate these two operations in their UI and may only offer leaving without forgetting a room. Thus, some servers automatically forget rooms when a user leaves them in order to more aggressively free up their resources. One example of this is the forget_rooms_on_leave config option in Synapse.

The present proposal seeks to standaradize this proprietary behaviour.

Proposal

When a user leaves a room, either through /_matrix/client/v3/rooms/{roomId}/leave or by being kicked or banned, Servers MAY automatically forget the room – as if the user had called /_matrix/client/v3/rooms/{roomId}/forget themselves.

This can limit clients' options to maintain an archive of historic rooms (such that they have left without forgetting them). Therefore, servers that auto-forget rooms MUST advertise that they do so via an m.forget_forced_upon_leave capability.

{
  "capabilities": {
    "m.forget_forced_upon_leave": {
      "enabled": true
    }
  }
}

A value of true means that the server performs auto-forget so that the client cannot leave rooms without also forgetting them. A value of false means that rooms will only be forgotten when the clients calls /_matrix/client/v3/rooms/{roomId}/forget.

When the capability is missing, clients SHOULD assume that the server does not auto-forget.

Potential issues

None.

Alternatives

None.

Security considerations

None.

Unstable prefix

While this proposal is unstable, clients should refer to m.forget_forced_upon_leave as org.matrix.msc4267.forget_forced_upon_leave.

Dependencies

None.