I rarely use this information in my program for serious purposes so I just stuff with REMOTE_HOST || REMOTE_ADDR, which will give me at least the IP address. If the request came by proxy than I would get that proxy IP address instead. I know there exists HTTP headers to distinguish these proxies in between, but I'll always have to lookup the references over the Internet to recall again about HTTP_VIA and HTTP_X_FORWARDED_FOR.

Here's a page discussing various proxy types and how they fill in those related HTTP headers. It would tell you right away your IP address, whether you're coming by a proxy, and if so, the proxy's IP address as well. You seem to have really consider it if you need accurate remote host or IP address information.