vpn.go

package main

import (
	"log"
	"net"
	"os/exec"

	"github.com/hsheth2/water"
)

var (
	Iface    = "192.168.137.2/24"
	Dest     = "192.168.137.1:8001"
	BindAddr = ":8001"
)

func createIface() (*water.Interface, error) {
	ifce, err := water.NewTUN("tun0")
	if err != nil {
		return nil, err
	}
	if err := exec.Command("ip", "link", "set", "tun0", "up").Run(); err != nil {
		return nil, err
	}
	if err := exec.Command("ip", "addr", "add", Iface, "dev", "tun0").Run(); err != nil {
		return nil, err
	}
	return ifce, nil
}

func main() {
	ifce, err := createIface()
	if err != nil {
		log.Fatal(err)
	}
	go listenInterface(ifce)
	addr, err := net.ResolveUDPAddr("udp", BindAddr)
	if err != nil {
		log.Fatal(err)
	}

	/* Now listen at selected port */
	conn, err := net.ListenUDP("udp", addr)
	if err != nil {
		log.Fatal(err)
	}
	defer conn.Close()

	buf := make([]byte, 1500)

	for {
		n, _, err := conn.ReadFromUDP(buf)
		packet := buf[0:n]
		if err != nil {
			log.Println("Error: ", err)
		}
		_, err = ifce.Write(packet)
		if err != nil {
			log.Println(err)
		}
	}

}

func listenInterface(ifce *water.Interface) {

	buffer := make([]byte, 1500)

	for {
		n, err := ifce.Read(buffer)
		if err != nil {
			log.Println(err)
			continue
		}
		if n > 0 {

			packet := buffer[0:n]
			addr, err := net.ResolveUDPAddr("udp", Dest)
			if err != nil {
				log.Println(err)
			}

			local, err := net.ResolveUDPAddr("udp", "127.0.0.1:0")
			if err != nil {
				log.Println(err)
			}

			conn, err := net.DialUDP("udp", local, addr)
			if err != nil {
				log.Println(err)
			}
			defer conn.Close()
			conn.Write(packet)
		}

	}
}