Ok, it looks like I can emulate it with TCP from info in this old post : http://mailman.nginx.org/pipermail/nginx/2007-June/001069.html
> No, I do not plan to add piped logs.
> However, you can use named pipe (FIFO).
>
> Also you can use the post_action to track downloading:
>
> location /xar/ {
> internal;
>
> root ...;
> post_action /done;
> }
>
> location = /done {
> internal;
>
> fastcgi_pass ...
> fastcgi_param URI $request_uri;
> ....
> }