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Kegan DougalandEric Eastwood
54c0a78f76
Adds the serving functions needed for MSC4242: State DAGs. This PR adds MSC4242 support to /make_join, /send_join and /get_missing_events, as well as calculates the destinations for /send events correctly using `prev_state_events`. Built on top of https://github.com/element-hq/synapse/pull/19718 for the storage functions it makes. Split out from https://github.com/element-hq/synapse/pull/19425 Part of a series of 5x PRs to land the federation part of [MSC4242](https://github.com/matrix-org/matrix-spec-proposals/pull/4242) ([storage](https://github.com/element-hq/synapse/pull/19718), [fedclient](https://github.com/element-hq/synapse/pull/20127), serving (this PR), inbound-joins, inbound-pulls). Whilst this is mostly a port of the code in #19425 there are a few changes: - `/get_missing_events` accepts message events when walking the state DAG, in which case it resolves the first hop to be that event's `prev_state_events`. The original PR made the client `/event` the message event and then set `latest=[prev_state_events]` on its own. This is not very efficient (extra round trip to fetch the event) and there's no reason why the server can't do the message->prev_state_events lookup, so we do so. This matches the MSC examples. - We cap the amount of events fetched via `/get_missing_events`. The MSC allows it, so it's a good safety check. - We sort the returned state DAG in `/send_join` by depth then event ID so it's "mostly" sorted. This is more a formality than anything else, the MSC does not mandate this, but it makes `/send_join` responses deterministic. - `notify_on_event_delivered_over_federation` is a new thing since #19425, so we include state DAG events in it like we do with state/auth_chain. This PR does remove the forced `m.federate: false` setting for MSC4242 rooms, so it makes it possible for federated MSC4242 rooms to be made. This is mostly so we can test via the endpoints. Given you must opt-in to MSC4242 via the experimental features config option, it seems reasonable to loosen this setting. The forced no-federation flag existed prior to review saying that the MSC4242 room version could itself be gated behind an experimental feature. Reviewable commit-by-commit. ### 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 <erice@element.io>