A function to get your IP address from ipify.org. It doesn't use any libraries and writes raw input in connection.

ipify.rs

use std::net::{TcpStream};
use std::io::{Write, BufReader, BufRead};

/// Connects to api.ipify.org and returns your IP address
/// Note that this method does not use any proxies
fn get_ip() -> Result<String, String> {
    // at first, try to to connect to ipify
    match TcpStream::connect("api.ipify.org:80") {
        Ok(mut stream) => {
            // create the request header; This is a const value
            let msg = b"GET / HTTP/1.1\r\nHost: api.ipify.org\r\nConnection: close\r\n\r\n";
            match stream.write(msg) { // write the header to stream
                Ok(_) => {
                    let stream = BufReader::new(stream); // wrap stream to buf reader to read it line by line
                    let mut lines = stream.lines().map(|l| l.unwrap());
                    // read the first line of stream to make sure we got 200
                    match lines.next() {
                        Some(line) => {
                            if !line.ends_with("200 OK") {
                                return Err(String::from(format!("Server didn't return code 200! Code {} is returned.", line)));
                            }
                        }
                        None => {
                            return Err(String::from("Empty body from server"));
                        }
                    }
                    // read all next lines until we reach an "empty line". After that, the next line is the IP address
                    loop {
                        match lines.next() {
                            Some(line) => {
                                if line.len() == 0 { // check if the have reached the empty line
                                    return Ok(lines.next().unwrap());
                                }
                            }
                            None => {
                                break;
                            }
                        }
                    }
                }
                Err(e) => { return Err(String::from(format!("Cannot write server's buffer: {}", e))); }
            }
        }
        Err(e) => {
            return Err(String::from(format!("Cannot connect to server: {}", e)));
        }
    };
    return Err(String::from("Empty body from server"));
}

fn main() {
    println!("{:?}", get_ip());
}