NAT traversal is an impossible problem in practice in the general case (boo symmetric NATs), and the best-effort version is a solved problem since at least 2003 with the STUN protocol[1] which is part of WebRTC, and there are STUN implementations available in many languages[2].

[1]: https://datatracker.ietf.org/doc/html/rfc3489 [2]: For instance, Rust: https://github.com/webrtc-rs/stun & Go:https://github.com/pion/stun, and see this HN comment listing a few WebRTC implementations (which include STUN): https://news.ycombinator.com/item?id=26739253