TUN example in Go

package main

import (
    "io"
    "net"
    "os"
    "fmt"
    "strings"
    "syscall"
    "unsafe"
)

const (
    cIFF_TUN   = 0x0001
    cIFF_NO_PI = 0x1000
)

const (
    cMAX_PACKET_SIZE = 1500 //MTU
)

type ifReq struct {
    Name  [0x10]byte
    Flags uint16
    pad   [0x28 - 0x10 - 2]byte
}

type tunIF struct {
    name string
    file *os.File
}

func (tun *tunIF) Name() string {
    return tun.name
}

func (tun *tunIF) createInterface(ifPattern string) (err error) {
    var req ifReq
    req.Flags = cIFF_TUN | cIFF_NO_PI
    copy(req.Name[:], ifPattern)
    _, _, errno := syscall.Syscall(syscall.SYS_IOCTL, tun.file.Fd(), uintptr(syscall.TUNSETIFF), uintptr(unsafe.Pointer(&req)))
    if errno != 0 {
        return errno
    }
    tun.name = strings.Trim(string(req.Name[:]), "\x00")
    return
}

func newTun(ifPattern string) (tun *tunIF, err error) {
    file, err := os.OpenFile("/dev/net/tun", os.O_RDWR, 0)
    if err != nil {
        return nil, err
    }
    tun = &tunIF{name: "", file: file}
    err = tun.createInterface(ifPattern)
    if err != nil {
        file.Close()
        return nil, err
    }
    return
}

// Read a packet from TUN device. 
func (tun *tunIF) Read() (packet []byte, err error) {
    buf := make([]byte, cMAX_PACKET_SIZE)
    n, err := tun.file.Read(buf)
    if err != nil && err != io.EOF {
        return
    }
    packet = buf[:n]
    return packet, nil
}

// Write a packet into TUN device (blocking)
func (tun *tunIF) Write(packet []byte) (err error) {
    _, err = tun.file.Write(packet)
    return
}

func IPFrom(bytes []byte) net.IP {
    return net.IPv4(bytes[0], bytes[1], bytes[2], bytes[3]).To4()
}

func main() {
    tun, err := newTun("tun0")
    if err != nil{
        fmt.Println(err)
    }
    for {
        packet, err := tun.Read()
        if err != nil {
            break
        }
        fmt.Printf("From: %v; To: %v\n", IPFrom(packet[12:16]), IPFrom(packet[16:20]))
    }
}