Cancellable requests

[MadLittleMods]

If someone cancels a long-running request in their browser, will we stop trying to talk to the Matrix homeserver? I assume we will continue to process the request as if nothing happened and seems to be the case according to https://stackoverflow.com/questions/35198208/handling-cancelled-request-with-express-node-js-and-angular

At the moment, the HTTP timeout for the app deployment in Red Hat OpenShift is 30 seconds while Synapse's timeout is 180 seconds (I think 120 seconds on matrix.org) so we often run into the scenario where the archive gets a 504 Gateway Timeout but are probably talking to the homeserver a lot more afterwards. Especially in some cases where every request is just slow (join, /timestamp_to_event, /context, /messages).

Synapse has recently been implementing cancellable requests so it will work on a granular level with them.

This is a minor thing for now so we can leave this for down the road.

Dev notes

I've implemented a cancellable request in Express once for the Gitter export resources since we stream out the data there and it can take a while.

let isRequestCanceled = false;
req.on('close', function() {
  isRequestCanceled = true;
});

---

Notes:

• fetch and AbortSignal, https://simonplend.com/how-to-cancel-an-http-request-in-node-js/