Element X doesn't check that the proxy responses are 2xx

[thibaultamartin]

Steps to reproduce

1. Deploy a homeserver on matrix.example.com behind a reverse proxy
2. Update the .well-known/matrix/client file so it responds the "org.matrix.msc3575.proxy": {"url": "https://matrix.example.com"}
3. Log in with Element X to example.com. The sync screen beings
4. The reverse proxy returns 404s for the sliding sync endpoints
5. Element X keeps spinning on the initial sync, not detecting that the sliding sync proxy is not here/not working

Outcome

What did you expect?

I expected the client to tell me that something's wrong

What happened instead?

The client tells me to wait forever

Your phone model

iPhone 11 Pro

Operating system version

iOS 17

Application version

Element X TF 1.2.9 (3)

Homeserver

Synapse 1.91 + Sliding Sync Proxy 0.99.10

Will you send logs?

No

[pixlwave]

From #1866:

Steps to reproduce

1. Set up synapse and a sliding sync server. Both available on :8448, synapse on :443 as well.
2. Forget to expose the sliding sync server on :443
3. Configure the .well-known to point to both servers (in my case: two subdomains, same apache)
4. Log in to server in Element X

Outcome

What did you expect?

• Element X figures out the host is not reachable and errors out

What happened instead?

• I am able to get all the way to "Setting up your account, this may take a while"
• Element X keeps on spinning, the phone gets fairly warm (though that might not be related)
• Sliding sync server obviously never gets contacted
• Even if I fully quit the app and restart it, it goes back to the spinning immediately

Application version

1.3.1 (74)

Homeserver

Synapse 1.93.0 / Sliding Sync 0.99.10

[teon]

Same here. I forgot to add to my DNS the sync host domain and had Setting up your account, this may take a while indefinitely...
Thanks to @pixlwave and this issue I got an idea how to fixed it ;-)

[pixlwave]

Linking this to matrix-org/matrix-rust-sdk#2822 which is what we need to detect the failure.