[PATCH] fastcgi_params: added REMOTE_HOST parameter

[Maxim Dounin]

Hello!

On Fri, Jan 12, 2024 at 05:04:22PM +0000, Jakub Zelenka wrote:

> Hi,
> 
> I'm a PHP-FPM maintainer and some FPM users have issues with missing host
> header when using HTTP/3: https://github.com/php/php-src/issues/13021 .
> This is not an nginx issue as correctly noted in
> https://trac.nginx.org/nginx/ticket/2281 but it would be nice to have
> fastcgi_param set for getting host in default config. I was thinking how to
> best expose $host and REMOTE_HOST seems logical and so I think it could be
> useful addition. I can update FPM to also set REMOTE_HOST from HTTP_HOST if
> REMOTE_HOST is not set which would make it even more available for HTTP/1.1
> and HTTP/2 users.
> 
> Please let me know what you think!
> 
> # HG changeset patch
> # User Jakub Zelenka <bukka at php.net>
> # Date 1705078404 0
> #      Fri Jan 12 16:53:24 2024 +0000
> # Node ID 1ff2f737bd318a730d0944a6037c8fd7c7da2656
> # Parent  ee40e2b1d0833b46128a357fbc84c6e23be9be07
> Added REMOTE_HOST parameter to fastcgi_params.
> 
> When HTTP/3 is used, users will no longer get HTTP_HOST as host header is no
> longer set by most clients. It is useful / necessary for many setups to have
> such information and REMOTE_HOST is defined in CGI/1.1 for such purpose.

https://datatracker.ietf.org/doc/html/rfc3875#section-4.1.9

   The REMOTE_HOST variable contains the fully qualified domain name of
   the client sending the request to the server, if available, otherwise
   NULL.

That is, REMOTE_HOST is completely unrelated.  It is not the 
hostname of the requested server, but the hostname of the client - 
result of a reverse DNS lookup of a client's IP address, something 
used to be provided by some servers when Internet was small (e.g, 
HostnameLookups in Apache).  It is certainly not the right param 
to use for $host.

IMO, proper param to use would be SERVER_NAME.  It is set to 
$server_name by default, though can be modified locally to provide 
$host if needed in the particular configuration.

> 
> diff -r ee40e2b1d083 -r 1ff2f737bd31 conf/fastcgi_params
> --- a/conf/fastcgi_params       Mon Dec 25 21:15:48 2023 +0400
> +++ b/conf/fastcgi_params       Fri Jan 12 16:53:24 2024 +0000
> @@ -17,6 +17,7 @@
> 
>  fastcgi_param  REMOTE_ADDR        $remote_addr;
>  fastcgi_param  REMOTE_PORT        $remote_port;
> +fastcgi_param  REMOTE_HOST        $host;
>  fastcgi_param  SERVER_ADDR        $server_addr;
>  fastcgi_param  SERVER_PORT        $server_port;
>  fastcgi_param  SERVER_NAME        $server_name;

-- 
Maxim Dounin
http://mdounin.ru/