2.6 KiB
MSC3567: Allow requesting events from the start/end of the room history
It can be useful to request the latest events in a room directly without calling
/_matrix/client/v3/sync first to fetch the room state. Some use-cases include:
- Requesting events using a different filter after receiving a
/syncresponse. - A client which does not need to fully sync an account, but wishes to inspect a specific room's history (perhaps for exporting or auditing).
Proposal
The from field on the /_matrix/client/v3/rooms/{roomId}/messages
becomes optional. If it is not provided, the homeserver shall return a list of
messages from the first or last (per the value of the dir parameter) visible
event in the room history for the requesting user.
Note that Synapse already implements this, but it is not spec-compliant. It is known to be used by Element Android 1 and Element Web, and there are other use-cases involving threads 2, which shows real-world usage that this would be valuable.
Ideally this would not be necessary and the prev_batch token received from
calling /sync could be provided as the pagination token to /messages, but this
will not work if you /sync with a filter that excludes a given class of event
(such as threaded replies), and all the events taking place in a room are of that
class. This will result in your /sync not returning an update for that room,
which means that your most recent prev_batch token precedes all the excluded
events. Trying to back-paginate from prev_batch using /messages will not
result in seeing the excluded events.
Potential issues
None.
Alternatives
The alternative is today's status quo: a client must first make a request to
/_matrix/client/v3/sync and then follow-up that request with queries to
/_matrix/client/v3/rooms/{roomId}/messages. This is clunky if the client is
going to throw away most of the information received from the /sync request.
The behavior also seems undefined if a different filter parameter is provided
for the call to /sync compared to the one used for /messages.
Security considerations
None.
Unstable prefix
Since this is modifying the endpoint to support not including a field, no unstable prefix is necessary.
Dependencies
N/A
-
In order to list all threads in a room without pulling the history locally it uses
/messagesto push the filtering onto the homeserver. See https://github.com/matrix-org/matrix-js-sdk/pull/2065 ↩︎