nat-punch: A Go repository from dev-rice

Simple UDP NAT Punchthrough

Implementation taken from https://en.wikipedia.org/wiki/UDP_hole_punching#Flow

Running the example

On some server with known, public IP:

go run cmd/introducer/main.go --listen-address :9001

On client A (can be anywhere)

go run cmd/client/main.go --introducer-address <introducer-ip>:9001

On client B (can be anywhere)

go run cmd/client/main.go --introducer-address <introducer-ip>:9001

After both clients connect to the introducer server, they will be able to send packets to each other without the need for any port forwarding rules. In this example, they just send their "secret number" to each other.

Example output:

Introducer

listening on :9001
read 16 bytes from 35.238.218.17:43155: hello introducer
read 16 bytes from 67.123.133.53:62917: hello introducer
sending peer info to 35.238.218.17:43155
sending peer info to 67.123.133.53:62917

Client A

wrote 16 bytes: hello introducer
read 19 bytes from 35.225.210.119:9001: 67.123.133.53:64097
introducer introduced me to peer '67.123.133.53:64097'
my secret number: 1844085407
sending secret number to 67.123.133.53:64097
read 31 bytes from 67.123.133.53:64097: hello. secret number: 554376187
sending secret number to 67.123.133.53:64097
read 31 bytes from 67.123.133.53:64097: hello. secret number: 554376187
sending secret number to 67.123.133.53:64097
read 31 bytes from 67.123.133.53:64097: hello. secret number: 554376187
sending secret number to 67.123.133.53:64097
read 31 bytes from 67.123.133.53:64097: hello. secret number: 554376187

Client B