A Go function for returning the current public IP address (supports both IPv4 and IPv6)

get_public_ip.go

package main

import (
	"fmt"

	"github.com/pion/stun"
)

func getPublicIP(ipType string) ([]string, error) {
	var network string = "udp4"

	if ipType == "ipv6" {
		network = "udp6"
	}

	var ips []string = []string{}

	// Connect to a public STUN server (Google maintains a free one)
	c, err := stun.Dial(network, "stun.l.google.com:19302")
	if err != nil {
		return ips, err
	}

	defer c.Close()

	// Create a message to "bind" (ask for our address)
	message := stun.MustBuild(stun.TransactionID, stun.BindingRequest)

	var err_ error = nil

	// Send the request and wait for a response
	if err := c.Do(message, func(res stun.Event) {
		if res.Error != nil {
			err_ = res.Error
		} else {
			// Decode the XOR-MAPPED-ADDRESS attribute
			var xorAddr stun.XORMappedAddress

			if err := xorAddr.GetFrom(res.Message); err != nil {
				err_ = err
			} else {
				publicIP := xorAddr.IP.String()

				ips = append(ips, publicIP)
			}
		}
	}); err != nil {
		return ips, err
	}

	if ipType == "both" {
		ipv6Query, err := getPublicIP("ipv6")
		if err == nil {
			ips = append(ips, ipv6Query[0])
		}
	}

	return ips, err_
}

func main() {
  fmt.Println(getPublicIP("")) // retrieve the IPv4
  fmt.Println(getPublicIP("ipv6")) // retrieve the IPv6
  fmt.Println(getPublicIP("both")) // retrieve both IP types
}