Reading/Writing Mac's TUN/TAP device using Go.

tun-ping-mac.go

package main

import (
	"exec"
	"log"
	"os"
)

func main() {
	file, err := os.Open("/dev/tun0", os.O_RDWR, 0)
	if err != nil {
		log.Exitf("error os.Open(): %v\n", err)
	}

	cmd, err := exec.Run("/sbin/ifconfig",
		[]string{"ifconfig", "tun0", "192.168.7.1", "192.168.7.2", "up"},
		nil, ".", 0, 1, 2)
	if err != nil {
		log.Exitf("error exec.Run(): %v\n", err)
	}
	cmd.Wait(0)

	for {
		buf := make([]byte, 2048)
		read, err := file.Read(buf)
		if err != nil {
			log.Exitf("error os.Read(): %v\n", err)
		}

		for i := 0; i < 4; i++ {
			buf[i+12], buf[i+16] = buf[i+16], buf[i+12]
		}
		buf[20] = 0
		buf[22] = 0
		buf[23] = 0
		var checksum uint16
		for i := 20; i < read; i += 2 {
			checksum += uint16(buf[i])<<8 + uint16(buf[i+1])
		}
		checksum = ^(checksum + 4)
		buf[22] = byte(checksum >> 8)
		buf[23] = byte(checksum & ((1 << 8) - 1))

		_, err = file.Write(buf)
		if err != nil {
			log.Exitf("error os.Write(): %v\n", err)
		}
	}
}