JupyterHUB: progress API updates blocked by configurable-http-proxy

[lflis]

Hi.
JupyterHUB 4.0.2, CHP 0.3.0
Recently we came across the problem where progress page in jupyterhub was not updated until notebook spawning was complete.

We have narrowed down the issue to CHP blocking chunked-responses from jupyterhub api until response generation is complete. What's more, request times out after 20 seconds.

progress API is using keep-alive connection and sends chunked response to the client. It is based on XHR connection (event-type/stream).
CHP here:

• prevents Connection-type: keep-alive header from reaching the api server (changed to close),
• keeps keepalive packets sent by API from passing until response is complete
• keeps chunked updates (self.write(), yield self.flush()) from passing thru the proxy

This functionaly works properly in NPM counter part.

[AbdealiLoKo]

Hi thanks the the report - did a quick check and seems like I can reproduce the issue

Would you like to attempt a fix with a PR?

[lflis]

@AbdealiLoKo thank you for confirming the issue.

Would you like to attempt a fix with a PR?

Unfortunately i don't have a quickfix nor PR yet. I'm not very familiar with CHP architecture either so it may take some time for me to come up with a camera ready solution.

I guess you might have better idea on sensible fix it so feel free to patch.