Remove default timeout on Sync

[pik]

There is currently no backup strategy for low-bandwidth connections which cannot complete a /sync within localTimeoutMs -- this means that slow connections will never load riot-web as the set of state events even for several popular rooms is very large - this removes the localTimeoutMs entirely from the default /sync calls (it can still be set via client.opts) as per element-hq/element-web#2737 (comment).

[ara4n]

I wonder whether removing the client timeout means that if you lose your connectivity during a sync (e.g. by sleeping your laptop, or switching network, etc), the sync will never timeout and the client will never recover from the outage, wedging solid.

Unless the keepAlives logic is adequate to recover from that scenario...

@kegsay, wdyt?

[pik]

The browser should fail with either, net::ERR_INCOMPLETE_CHUNKED_ENCODING net::ERR_NETWORK_CHANGED etc. I think? Is there a case where the browser might not set request status to failed ? The errors should be handled here: https://github.com/matrix-org/matrix-js-sdk/blob/develop/src/sync.js#L554 and a sync retried after keepalive?

[kegsay]

In practice, browsers do not fail and just wedge entirely. Notably, Safari does this. This is why localTimeoutMs is A Thing. I can't accept this PR because it will break other users.

[pik]

In practice, browsers do not fail and just wedge entirely. Notably, Safari does this

Really? In my testing both Firefox and Chromium fail correctly, is there an open bug for this in Safari?

At any-rate if this is a possibility we have to contend with - what about hooking into onprogress to debounce the timeout event?

[kegsay]

what about hooking into onprogress to debounce the timeout event?

That's what I would prefer.

[richvdh]

I think this got superceded by #330, and thence #392.