extip.rs

use std::io::net;

fn get_my_external_ip() -> Option<net::ip::IpAddr> {
    net::tcp::TcpStream::connect("8.8.8.8", 53).and_then(|ref mut s| s.socket_name()).map(|a| a.ip).ok()
}

fn main() {
    println!("My external IP: {}", get_my_external_ip());
}

$ rustc ./extip.rs
$ ./extip
My external IP: 192.168.1.200