MSC4476: Image pack rooms

proposals/4476-image-pack-rooms.md

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+# MSC4476: Image pack rooms
+
+[MSC2545](https://github.com/matrix-org/matrix-spec-proposals/pull/2545) introduced image packs for storing stickers and
+custom emojis in room state. While packs can be enabled globally via `m.image_pack.rooms` account data, there is
+currently no way to create standalone image packs that are not tied to a normal joined room or space.
+However, users may wish to create and share image packs independently of such existing chat rooms or communities,
+similar to how other chat networks like Telegram or Signal handle sticker packs.
+
+Accordingly, this proposal introduces a new room type dedicated to image pack usage, that allows clients to decouple
+image pack handling from traditional room and space UI.
+
+
+## Proposal
+
+A new room type, `m.image_pack`, is introduced. Similar to
+[spaces](https://spec.matrix.org/v1.18/client-server-api/#spaces)
+(rooms configured as `m.space`), message sending should be disabled by default, as the main purpose of such rooms is to
+hold `m.image_pack` state events. Furthermore, new image pack rooms are recommended to be configured as public rooms,
+e.g. to allow users to share rooms by URL via
+[traditional means of linking rooms](https://spec.matrix.org/v1.18/appendices/#uris).
+Clients are still allowed to configure arbitrary join rules as desired.
+
+Upon successful creation of an `m.image_pack` room, clients should add the new room ID to the user's `m.image_pack.rooms`
+account data, since the user likely expects being able to use the new pack they created globally right away. Users may
+however still decide to not enable these packs globally, e.g. when they only want to maintain a sticker pack for other
+users without using it themselves. Accordingly, the presence of dedicated image pack rooms should not affect the logic
+of which image packs to enable globally, i.e. `m.image_pack.rooms` account data remains the single source of truth in
+this regard, and clients are allowed to expose suitable settings to users accordingly.
+
+Managing image packs in dedicated image pack rooms works as before on a technical level, i.e., as defined by
+[MSC2545](https://github.com/matrix-org/matrix-spec-proposals/pull/2545). Clients should however present such rooms
+in a different way to the user, e.g. in some dedicated image pack settings screen, rather than in the room list
+dedicated to chat rooms. Since a room may hold multiple image packs, clients may want to refer to image pack rooms as
+"image pack collections" or similar.
+
+
+## Potential issues
+
+#### User expectations for sharing image packs may not match the Matrix room model
+
+Since importing an image pack involves joining a room, this action will naturally expose the user's room membership to
+other members of this room. Users may not expect this implication, as it is not common on other networks.
+
+Maybe a future MSC could introduce the concept of "broadcast rooms" of some kind, in which the server hides the
+membership of other users in a room, which would then also be a natural fit for image pack rooms.
+Another approach would be some kind of federated room peeking mechanism, such that users can read image pack rooms
+without actually joining. For the time being, clients are encouraged to educate users about the implications of
+joining the image pack room.
+
+
+## Alternatives
+
+One could try to invent a completely new primitive that does not build on rooms, e.g. in order to allow sharing packs
+without leaking room membership. New primitives add complexity both for clients and servers and can probably not be
+justified for image packs.
+
+
+## Security considerations
+
+The mismatch between user expectations and the fact that importing image packs involves room membership, as outlined in
+potential issues, may be considered a security consideration, if users are not properly educated.
+
+Apart from that, none.
+
+
+## Unstable prefix
+
+`com.beeper.image_pack` can be used as room type instead of `m.image_pack`.
+
+
+## Dependencies
+
+This MSC builds on [MSC2545](https://github.com/matrix-org/matrix-spec-proposals/pull/2545), which has recently been
+accepted and merged.
+
+This MSC can furthermore naturally be combined with
+[MSC4459](https://github.com/matrix-org/matrix-spec-proposals/pull/4459) to link image pack rooms from sent stickers and
+emotes, but both can be useful independently, so it is not a dependency.