Not necessarily. That code could be written assuming it is running behind a reverse proxy/other infrastructure (that would obviously strip/replace any x-forward

Not necessarily. That code could be written assuming it is running behind a reverse proxy/other infrastructure (that would obviously strip/replace any x-forwarded-for etc. provided by the user). The comments seem to indicate it is running behind a proxy of the author's choosing, but that may just be bad English. At the very least something has to be providing that HTTP_CLIENT_IP which is given the highest priority. It would be odd to prioritize that over HTTP_X_FORWARDED_FOR if you weren't adding special cases for different upstream proxies.