[FIX] runbot: forward X-Accel-Buffering header for streaming responses

[caburj]

Because of multi-layered use of nginx, responses with "X-Accel-Buffering: no" is still buffered because the special header is absorbed by layer just above the odoo app. As a result, it's impossible to test in runbot endpoints that stream responses. To ensure that header is respected thoughout the stack, we propose in this commit to pass the "X-Accel-Buffering" header.

[Julien00859]

This is a very bad idea.

First the code is not correct, proxy_pass_header is about adding a header on on request to be forwarded, not about adding a header on the response. You meant add_header.

But preventing nginx from buffering most responses (location /) is absolutely madness. Don't do that.

[Julien00859]

There should be some code that check for the presence of the X-Accel-Buffering header on the original response, and repeat it on the forwarded response.

[caburj]

My goal is to stream response and prevent the buffering so that the client won't receive the streamed data at once, thus, I'm adding an nginx custom header "x-accel-buffering: no" which is actually suggested from the docs of proxy_buffering (https://nginx.org/en/docs/http/ngx_http_proxy_module.html#proxy_buffering).

"Buffering can also be enabled or disabled by passing “yes” or “no” in the “X-Accel-Buffering” response header field."

First the code is not correct, proxy_pass_header is about adding a header on on request to be forwarded, not about adding a header on the response. You meant add_header.

The docs (https://nginx.org/en/docs/http/ngx_http_proxy_module.html#proxy_pass_header) says otherwise:

proxy_pass_header: "Permits passing otherwise disabled header fields from a proxied server to a client."

Note: server to client so it pertains to the response. There is proxy_pass_request_header for requests (https://nginx.org/en/docs/http/ngx_http_proxy_module.html#proxy_pass_request_headers).

But preventing nginx from buffering most responses (location /) is absolutely madness. Don't do that.

proxy_buffering is "on" by default. To escape the buffering for specific responses, they suggest to add a response header called "x-accel-buffering: no". This is what I'm doing in the referenced enterprise PR. I'm just exceptionally disabling buffering for a certain endpoint. I'm not disabling the buffering for location /. I didn't put proxy_buffering off;.

[Julien00859]

You are right about everything! I got proxy_pass_header mixed with proxy_set_header. What does it mean for X-Accel-Redirect? that specific header should be interpreted by nginx and not copied to the next hop.

[caburj]

I can't imagine a connection between "X-Accel-Buffering" and "X-Accel-Redirect", they seem independent. But I suppose "X-Accel-Redirect" isn't affected by the proposed change because the change is very specific to "X-Accel-Buffering".