server: add "X-Accel-Buffering": "no" header to streaming endpoints

[regunakyle]

Overview

This header tells Nginx (as a reverse proxy with SSL) to NOT buffer responses.
Only streaming endpoints are affected. The header does nothing if Nginx is not involved.
Without it, Nginx will break streaming with certain applications (notably the Pi coding harness).
Nginx docs for reference

Requirements

• I have read and agree with the contributing guidelines
• AI usage disclosure: YES, for codebase exploration

[pnb]

This is great! I haven't had buffering actually break anything yet, but it was annoying me a bit because the text comes out of the server quite chunky and harder to read versus a smooth stream. I switched computers, internet connections, and reverse proxies at the same time, so I had assumed it was the internet or computer rather than switching from Apache to Nginx, but in fact this fixes it.

[ServeurpersoCom]

It costs nothing to add it. I haven't encountered this issue with Apache2/pi
well-known header in nginx, and the line is in the right place.

[ngxson]

not 100% sure but will this be set one more time in router mode ?

[ServeurpersoCom]

not 100% sure but will this be set one more time in router mode ?

I check if it passes through!
That reminds me of the issue with the duplicate headers that we fixed.

[ServeurpersoCom]

OK, on router, it works, and only one at that. Just note that it will apply to all endpoints.

[ngxson]

I mean, does the router add the same header once again? (i.e. duplicated header)

[ngxson]

nvm, headers is a map, so it's not possible to have duplicated keys

[ServeurpersoCom]

I meant, no duplicates.

[regunakyle]

OK, on router, it works, and only one at that. Just note that it will apply to all endpoints.

Pretty sure only streaming endpoints are affected. Non-streaming endpoints like /props and /models are not affected.

BTW as a note, Nginx will strip out the X-Accel-Buffering header before sending the proxied response back to the user.