How to get the port used by the request

Hello,

When a request is handled by mod_perl, I'd like to know what port was used
to request the server. But $r->server->port always returns 0. I have tested
$r->main and $r->prev, but the problem doesn't come from here. And I didn't
find any other way to get the port. Even $r->uri and such don't return the
port, even though $r->hostname returns the server hostname. Where is my
mistake?

Thanks for your time.