Re: [RFC] http_response: ignore invalid header response characters

[Eric Wong <bofh@yhbt.net>]

cf. https://yhbt.net/unicorn-public/20201126115902.GA8883@dcvr/T/

This RFC patch isn't necessary and it's a waste of CPU cycles
for existing users returning valid responses.

I've confirmed nginx will return 502 (Bad Gateway) errors if
either the header key OR header value have "\r" (CR) in it.  The
client never sees the bad response through nginx, only the 502
from nginx.

For anybody unfamiliar with unicorn: unicorn was always designed
to have nginx in front of it, otherwise clients can trivially
DoS it.

I tested with nginx/1.14.2 on Debian stable (10.x).  Also,
varnish/6.1.1 (again on Debian stable) will fail with a 503
error when it sees "\r" in either the header key or value
(nowadays I rely on varnish quite a bit)

Again, thanks for the concern, but no action is necessary for
correctly configured deployments using nginx with or w/o varnish.

The following config.ru can be edited by uncommenting either
of the "cr*" lines to trigger the 502 from nginx.  Leaving
both lines commented shows a 200 "HI\n" response as expected.

==> config.ru <==
#\-E none
use Rack::CommonLogger
run lambda { |env|
  [ 200, {
     'Content-Type' => 'text/plain',
     'Content-Length' => '3',
     # uncommenting either of the following lines causes nginx to 502
     # varnish will 503
     #  "cr\rkey" => "cr-key",
     #  "cr-val" => "cr\rkey",
    },
    [ "HI\n" ]
  ]
}