Is this a feature request? Yes

I'd like to use ExpressJS and delegate to Nginx on the same machine.
Nginx listens on "unix:/home/simba/gateway.sock" instead of a port number.
http://nginx.org/en/docs/http/ngx_http_core_module.html#listen

server
{
    listen       unix:/home/simba/gateway.sock;
    server_name  navicore.mapbar.com;
    ...
}

From my past experience, Unix domain socket has much less connection overhead.
Even without "connection: keep-alive", the performance will be maximized.

So is it possible to add this support?