tun.go

package main

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

	"golang.org/x/net/ipv4"

	"github.com/songgao/water"
)

const (
	// I use TUN interface, so only plain IP packet, no ethernet header + mtu is set to 1300
	BUFFERSIZE = 1600
	MTU        = "1300"
)

func main() {
	iface, err := water.New(water.Config{})
	fatalIf(err)

	log.Printf("tun interface: %s", iface.Name())
	runBin("/bin/ip", "link", "set", "dev", iface.Name(), "mtu", MTU)
	runBin("/bin/ip", "addr", "add", "10.2.0.10/24", "dev", iface.Name())
	runBin("/bin/ip", "link", "set", "dev", iface.Name(), "up")

	buf := make([]byte, BUFFERSIZE)

	for {
		n, err := iface.Read(buf)
		if err != nil {
			log.Fatal(err)
		}

		header, _ := ipv4.ParseHeader(buf[:n])

		log.Printf("isTCP: %v, header: %s", header.Protocol == 6, header)
	}
}

func fatalIf(err error) {
	if err != nil {
		log.Fatal(err)
	}
}

func runBin(bin string, args ...string) {
	cmd := exec.Command(bin, args...)
	cmd.Stderr = os.Stderr
	cmd.Stdout = os.Stdout
	cmd.Stdin = os.Stdin
	fatalIf(cmd.Run())
}

https://gist.github.com/aofei/563636c7cca9eceef403bb9983e4f190