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|
package main
import (
"encoding/binary"
"errors"
"os"
"strings"
"syscall"
"unsafe"
)
/* Implementation of the TUN device interface for linux
*/
const CloneDevicePath = "/dev/net/tun"
type NativeTun struct {
fd *os.File
name string
}
func (tun *NativeTun) Name() string {
return tun.name
}
func (tun *NativeTun) MTU() (int, error) {
// open datagram socket
fd, err := syscall.Socket(
syscall.AF_INET,
syscall.SOCK_DGRAM,
0,
)
if err != nil {
return 0, err
}
// do ioctl call
var ifr [64]byte
var flags uint16
copy(ifr[:], tun.name)
binary.LittleEndian.PutUint16(ifr[16:], flags)
_, _, errno := syscall.Syscall(
syscall.SYS_IOCTL,
uintptr(fd),
uintptr(syscall.SIOCGIFMTU),
uintptr(unsafe.Pointer(&ifr[0])),
)
if errno != 0 {
return 0, errors.New("Failed to get MTU of TUN device")
}
// convert result to signed 32-bit int
val := binary.LittleEndian.Uint32(ifr[16:20])
if val >= (1 << 31) {
return int(val-(1<<31)) - (1 << 31), nil
}
return int(val), nil
}
func (tun *NativeTun) Write(d []byte) (int, error) {
return tun.fd.Write(d)
}
func (tun *NativeTun) Read(d []byte) (int, error) {
return tun.fd.Read(d)
}
func CreateTUN(name string) (TUNDevice, error) {
// open clone device
fd, err := os.OpenFile(CloneDevicePath, os.O_RDWR, 0)
if err != nil {
return nil, err
}
// prepare ifreq struct
var ifr [64]byte
var flags uint16 = syscall.IFF_TUN | syscall.IFF_NO_PI
nameBytes := []byte(name)
if len(nameBytes) >= syscall.IFNAMSIZ {
return nil, errors.New("Name size too long")
}
copy(ifr[:], nameBytes)
binary.LittleEndian.PutUint16(ifr[16:], flags)
// create new device
_, _, errno := syscall.Syscall(
syscall.SYS_IOCTL,
uintptr(fd.Fd()),
uintptr(syscall.TUNSETIFF),
uintptr(unsafe.Pointer(&ifr[0])),
)
if errno != 0 {
return nil, errors.New("Failed to create tun, ioctl call failed")
}
// read (new) name of interface
newName := string(ifr[:])
newName = newName[:strings.Index(newName, "\000")]
return &NativeTun{
fd: fd,
name: newName,
}, nil
}
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