Stabilize support for MSC2946: spaces summary

[clokep]

Once MSC2946 lands we should (at some point) switch to a stable endpoint and make some updates. There's few bits to this that we need to do:

Phase 1

• Support to the stable endpoint.
• Require limit to be > 0. (This has always been correct.)
• Ensure the endpoint is ratelimited.

Phase 2

• Remove the fallback logic of get_room_hierarchy to request the /spaces endpoint over federation.
• Remove the /spaces client and federation endpoints (and corresponding code in the handlers).
• Update the API responses to remove allowed_spaces (this was replaced with allowed_room_ids).
• Clean-up code around max-children, which is not used by the /hierarchy endpoint.
• Remove room_id from the serialized children_state, it is redundant and removed from the API response.

Phase 3

• Remove unstable /hierarchy client and federation endpoints.
• Remove the typo join_rules field from the response.

[clokep]

I think this work needs to be split into a few pieces.

Phase 1:

• Support the stable endpoint.
• Remove some of the legacy code (the /spaces endpoint? and surrounding bits?)
• Enforce the limit / ratelimiting.

Phase 2:

• Remove the unstable /hierarchy endpoint.

[clokep]

Remove some of the legacy code (the /spaces endpoint? and surrounding bits?)

It looks like these endpoints still get some usage on matrix.org, so might be best to just leave them for now and remove all the unstable code at once.

[clokep]

Client bugs for using the stable endpoint:

• Use the stable hierarcy endpoint from MSC2946 element-hq/element-ios#5144
• Use the stable hierarchy endpoint from MSC2946 element-hq/element-android#4462
• Use the stable hierarchy endpoint from MSC2946 element-hq/element-web#19738

The only other client I know of which implements spaces is Cinny, which uses the matrix-js-sdk.

See also element-hq/element-meta#84.

[clokep]

For phase 2 it is useful to know which version of clients first started using (unstable or stable) /hierarchy instead of /spaces.

• Element Android v1.2.1 (Feature/bca/space explore pagination element-hq/element-android#3926)
• matrix-ios-sdk v0.20.11 (Support pagination in the Space Summary API matrix-ios-sdk#1259)
  • Element iOS: v1.6.9 (https://github.com/vector-im/element-ios/blob/v1.6.9/Podfile#L16)
• matrix-js-sdk v12.4.0 (Add support for /hierarchy API and fall back to /spaces API if needed matrix-js-sdk#1818):
  • Element Web: v1.8.2 (https://github.com/vector-im/element-web/blob/v1.8.2/package.json#L64)
  • Cinny: v1.2.1 (https://github.com/ajbura/cinny/blob/v1.2.1/package.json#L27)

[clokep]

Note that I don't think Element iOS ever shipped a version using /spaces? I think before v1.6.9 it didn't even have spaces support.

[turt2live]

Using our opt-in analytics to determine "market share" of each Element platform (where values at or near zero aren't considered) for the Feb 17th - 22nd period, the following conclusions can be drawn. Note that scraping user agents is likely to be more reliable, however I think given the numbers below it's safe enough to move forward.

TLDR: All platforms are reporting versions which exceed the minimum outlined by previous comments.

• iOS (requires 1.6.9+ to be safe):
  • 1.7.0 is at 21.61%
  • 1.8.1 is at 77.04%
• Android (requires 1.2.1+ to be safe):
  • 1.3.15 is at 7.00%
  • 1.3.18 is at 12.65%
  • 1.4.0 is at 79.89%
• Web (requires 1.8.2+ to be safe):
  • No data (reporting error)
• Desktop (requires 1.8.2+ to be safe):
  • No data (reporting error)

While I don't have data on Element Web/Desktop, 1.8.2 was August 2021 and it's now February - if people haven't updated, I don't hold hope that they will by now.