How to do a DNS lookup without any crates?

According to https://doc.rust-lang.org/std/net/trait.ToSocketAddrs.html#examples,

use std::net::{SocketAddr, ToSocketAddrs};

// assuming 'localhost' resolves to 127.0.0.1
let mut addrs_iter = "localhost:443".to_socket_addrs().unwrap();
assert_eq!(addrs_iter.next(), Some(SocketAddr::from(([127, 0, 0, 1], 443))));