diff --git a/proposals/4356-recent-emoji.md b/proposals/4356-recent-emoji.md new file mode 100644 index 00000000000..2473c89ad14 --- /dev/null +++ b/proposals/4356-recent-emoji.md @@ -0,0 +1,81 @@ +# MSC4356: Recently used emoji + +Like other chat platforms, Matrix supports emoji as a way to visually express ideas or emotions. In +practice, most people use a limited set of emoji only. Since emoji are commonly used as a quick way +to react to something, it is desirable for clients to offer users shortcuts to their favorite emoji. +Some emoji picker libraries support this feature by locally tracking emoji usage. This doesn't work +well in a multi-device environment, however, because such history cannot easily be shared between +clients. + +This proposal introduces a way for clients to maintain a shared storage of recently used emoji to +enable emoji suggestions across clients. + +## Proposal + +A new global account data event `m.recent_emoji` is introduced. In `content`, it contains a single +property `recent_emoji` that is an array where each element is itself an array. The first element in +this nested array is the emoji, the second element is a counter (\<= 2^53-1) for how often it was +used. The outer `recent_emoji` array is ordered descendingly by last usage time. + +``` json5 +{ + "type": "m.recent_emoji", + "content": { + "recent_emoji": [ + [ "😅", 7 ], // Most recently used, 7 times overall + [ "👍", 84 ], // Second most recently used, 84 times overall + ... + } +} +``` + +When an emoji is used in a message or an annotation, the sending client moves (or adds) it to the +beginning of the `recent_emoji` array and increments (or initializes) its counter. + +When an image is sent as an inline image or in a reaction (using [MSC4027]), the `mxc://` URI of the +image MAY be used as the "emoji" in this event. Clients which do not support such use of images MUST +tolerate the existence of `mxc://` entries, e.g. by ignoring the entries when deciding what to +display to the user, while still preserving them when modifying the list. + +As new emoji are being used, clients SHOULD limit the length of the `recent_emoji` array by dropping +elements from the end. A RECOMMENDED maximum length is 100 emoji. Apart from this, no other +mechanism for resetting counters is mandated as the upper boundary of 2^53-1 seems sufficiently +large for all practical purposes. + +Clients MAY freely customise the logic for generating recommendations from the stored emoji. As an +example, they could select the 24 first (= most recently used) emoji and stably sort them by their +counters (so that more recently used emoji are ordered first on ties). + +## Potential issues + +Clients could choose wildly different ways to generate recommendations from the shared storage +leading to significantly different UX across clients. + +## Alternatives + +Further metadata such as the concrete access time or the room could be tracked together with emoji. +It is unclear, however, if this would lead to materially better suggestions. + +## Security considerations + +This proposal doesn't mandate encrypting the `m.recent_emoji` account data event. Since emoji are +most commonly used in annotations which are not encrypted, servers could already track and abuse +this information today, however. + +Malicious or buggy clients could cause undefined behavior on other clients by setting emoji counters +to negative values or the maximum allowed value. To prevent this, clients SHOULD drop any emojis +with a count below 0 from the list. When observing a count of 2^53-1 for an emoji, clients SHOULD +normalise the entire set of emoji by dividing all counts by two and rounding up. To prevent race +conditions, both of these changes SHOULD only be applied when the client is updating the account +data event due to local emoji usage. + +## Unstable prefix + +While this MSC is not considered stable, `m.recent_emoji` should be referred to as +`io.element.recent_emoji`. + +## Dependencies + +None. + + [MSC4027]: https://github.com/matrix-org/matrix-spec-proposals/pull/4027