Part of #19414 (Support Matrix 1.16).
⚠️ Before merging, wait for the following PRs to be merged first:
- https://github.com/element-hq/synapse/pull/20081
- https://github.com/element-hq/synapse/pull/20169
- https://github.com/element-hq/synapse/pull/20171
---
Since Matrix 1.16, the
[spec](https://spec.matrix.org/v1.19/client-server-api/#get_matrixclientv3sync)
defines the stable identifiers for
[MSC4222](https://github.com/matrix-org/matrix-spec-proposals/pull/4222):
the `use_state_after` query parameter on `GET /_matrix/client/v3/sync`,
and the `state_after` room response field:
> **`use_state_after`** — `boolean` — Controls whether to receive state
changes between the previous sync and the start of the timeline, or
between the previous sync and the end of the timeline. If this is set to
`true`, servers MUST respond with the state between the previous sync
and the end of the timeline in `state_after` and MUST omit `state`. […]
>
> **`state_after`** — […] Required if `use_state_after` was set to true
in the request, even if it is empty. Added in `v1.16`
>
> — [Matrix
Spec](https://spec.matrix.org/v1.19/client-server-api/#get_matrixclientv3sync)
Synapse so far only implemented the unstable identifiers
(`org.matrix.msc4222.use_state_after` /
`org.matrix.msc4222.state_after`), gated behind the `msc4222_enabled`
experimental flag and the per-user experimental features admin API.
This PR:
- accepts the stable `use_state_after` query parameter, unconditionally,
and responds with the stable `state_after` field. The unstable query
parameter is kept for a transition period; clients opting in with it get
the unstable response field name back, so unstable-era clients see an
unchanged wire format. If both parameters are set, the stable one wins.
- removes the `msc4222_enabled` experimental flag and the `msc4222`
per-user feature from the experimental features admin API, since the
behaviour is no longer gated.
### Pull Request Checklist
<!-- Please read
https://element-hq.github.io/synapse/latest/development/contributing_guide.html
before submitting your pull request -->
* [x] Pull request is based on the develop branch
* [x] Pull request includes a [changelog
file](https://element-hq.github.io/synapse/latest/development/contributing_guide.html#changelog).
The entry should:
- Be a short description of your change which makes sense to users.
"Fixed a bug that prevented receiving messages from other servers."
instead of "Moved X method from `EventStore` to `EventWorkerStore`.".
- Use markdown where necessary, mostly for `code blocks`.
- End with either a period (.) or an exclamation mark (!).
- Start with a capital letter.
- Feel free to credit yourself, by adding a sentence "Contributed by
@github_username." or "Contributed by [Your Name]." to the end of the
entry.
* [x] [Code
style](https://element-hq.github.io/synapse/latest/code_style.html) is
correct (run the
[linters](https://element-hq.github.io/synapse/latest/development/contributing_guide.html#run-the-linters))
---------
Co-authored-by: Eric Eastwood <madlittlemods@gmail.com>
Basically, if the client sets a special query param on `/sync` v2
instead of responding with `state` at the *start* of the timeline, we
instead respond with `state_after` at the *end* of the timeline.
We do this by using the `current_state_delta_stream` table, which is
actually reliable, rather than messing around with "state at" points on
the timeline.
c.f. MSC4222
Follows on from @H-Shay's great work at
https://github.com/matrix-org/synapse/pull/15344 and MSC4026.
Also enables its use for MSC3881, mainly as an easy but concrete example
of how to use it.
