matrix-spec-proposals/proposals/3874-messages-endpoint-threads-filter.md

MSC3874 Loading Messages excluding Threads

Motivation

In Element's beta implementation of threads, it's become a noticeable issue where a room may have activity in a long-running thread while the main timeline is inactive. If a user starts their client and tries to paginate through the main timeline, loading will feel sluggish, as lots of events have to be loaded that won’t be displayed.

This proposal would allow reducing the number of requests and amount of data transmitted.

Proposal

Allow filtering the /messages API to not include threaded messages

This proposal recommends extending the existing Event filters are extended with a new filter, named not_related_by_rel_types, which acts exactly like the opposite of the existing related_by_rel_types filter.

This means, if this filter is specified, only message which match none of the given relation types will be returned.

GET /_matrix/client/unstable/org.matrix.msc3874/rooms/!room_id:domain/messages?filter=...

The filter string includes the new fields, above. In this example, the URL encoded JSON is presented unencoded and formatted for legibility:

{
  "types": ["m.room.message"],
  "not_related_by_rel_types": ["m.thread"]
}

Note that the newly added filtering parameters return events based on information in related events. Consider the following events in a room:

• A: a m.room.message event sent by alice
• B: a m.room.message event sent by bob
• C: a m.room.message event sent by charlie which relates to A with type m.thread

Using a filter of "not_related_by_rel_types": ["m.thread"] would return only event B as it has no event which relates to it via m.thread.

Server capabilities

Threads might have sporadic support across servers, to simplify feature detections for clients, a homeserver must advertise unstable support for threads as part of the /versions API:

{
  "unstable_features": {
    "org.matrix.msc3874": true,
    // ...
  }
}

Potential issues

This proposal moves the loading and processing of these hidden events onto the server. Depending on the server’s architecture, this may have a non-negligible performance impact.

Limitations

This proposal only considers events which have a direct relationship with the thread itself. Events such as reactions don’t, so they won’t be able to be filtered by this proposal.

Alternatives

• A suitable workaround, depending on the ratio of thread-messages compared to main timeline messages in a room, may be an increase of the page size

Dependencies

• MSC2674 ✓
• MSC2675 ✓
• MSC3567 ✓
• MSC3676 ✓
• MSC3440 ✓