Excessive calls to `GET /relations` and `GET /event`, with MSC3981 enabled and working

[turt2live]

Steps to reproduce

1. Restart app
2. Click around a couple rooms
3. Enjoy the flood of http requests

Outcome

What did you expect?

For the app to start up quickly, quietly (this bug causes my CPU fans to be fast-moving), and without duplicating requests.

What happened instead?

There's tens of thousands of requests, so haven't identified a pattern yet. A few example URLs are:

• https://t2l.io/_matrix/client/v1/rooms/!REDACTED:matrix.org/relations/$REDACTED/m.replace/m.room.encrypted?limit=1
• https://t2l.io/_matrix/client/v1/rooms/!REDACTED:element.io/relations/$REDACTED/m.replace/m.room.encrypted?limit=1
• https://t2l.io/_matrix/client/r0/rooms/!REDACTED:element.io/event/$REDACTED
• etc

Specifically on the GET /event calls, many appear to be duplicated:

I was told ages ago that MSC3981 would fix this, but it hasn't (or the scope of the MSC changed between 6 months ago and now).

Operating system

Windows 11

Application version

Element Nightly version: 0.0.1-nightly.2023051701 Olm version: 3.2.14

How did you install the app?

The Internet

Homeserver

t2l.io

Will you send logs?

Yes

[turt2live]

This can cause /sync to be suffocated of resources, making it impossible to actually keep up to date for upwards of 30-40 minutes (in my case)

[clokep]

I was told ages ago that MSC3981 would fix this, but it hasn't (or the scope of the MSC changed between 6 months ago and now).

I thought MSC3925 was meant to fix this, not MSC3981?

[turt2live]

I've just turned on MSC3981 support, and while it's reduced a lot of the /relations spam, I'm still seeing plenty of duplicated requests for GET /event.

[turt2live]

I spoke too soon: it's now spamming /relations too (same request as before).

[justjanne]

The implementation of MSC 3981 in element-web was actually slightly faulty, as it still did the old-style /relations requests (though ignored the results). This should be fixed now.

[turt2live]

/relations is indeed fixed (assuming server support is advertised). GET /event is 64% of all requests my client makes, though (as I understand it though, the /relations fix wouldn't have fixed this particular one).

[andybalaam]

@turt2live I assume your server supports MSC3981? Element Web won't use it unless the server advertises support for it.

[turt2live]

Yes, enabling MSC3981 support stopped the /relations spam, per above.

[richvdh]

Excessive calls to GET /relations and GET /event, with MSC3981 enabled and working [my emphasis]
Yes, enabling MSC3981 support stopped the /relations spam, per above.

These two statements seem to be in conflict. Which is correct?

In any case, I experienced much the same (cf #25705), and it doesn't seem to be making a /relations request for every event in the thread, so how would MSC3981 help?

[richvdh]

I think this is mis-triaged. It's basically a show-stopping DoS which happens every time you reload the app.