Function is_loopback_host 

fn is_loopback_host(host: &str) -> bool

Whether host is loopback: the localhost name, or any address in a loopback range. Every form counts, not three literals: 127.0.0.2, an expanded [0:0:0:0:0:0:0:1] and an IPv4-mapped [::ffff:127.0.0.1] are all this machine.