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@bcho
Created July 25, 2020 09:22
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package main
import (
"encoding/binary"
"fmt"
"net"
"os"
"unsafe"
"golang.org/x/sys/unix"
)
const (
tunDevice = "/dev/net/tun"
ifReqSize = unix.IFNAMSIZ + 64
)
func checkErr(err error) {
if err == nil {
return
}
panic(err)
}
// https://www.kernel.org/doc/Documentation/networking/tuntap.txt
// setup: ip link set up wg1 && ip addr add 10.0.1.2/24 dev wg1
// test: ping -c1 -b 10.0.1.255
func main() {
nfd, err := unix.Open(tunDevice, os.O_RDWR, 0)
checkErr(err)
var ifr [ifReqSize]byte
var flags uint16 = unix.IFF_TUN | unix.IFF_NO_PI
name := []byte("wg1")
copy(ifr[:], name)
*(*uint16)(unsafe.Pointer(&ifr[unix.IFNAMSIZ])) = flags
fmt.Println(string(ifr[:unix.IFNAMSIZ]))
_, _, errno := unix.Syscall(
unix.SYS_IOCTL,
uintptr(nfd),
uintptr(unix.TUNSETIFF),
uintptr(unsafe.Pointer(&ifr[0])),
)
if errno != 0 {
checkErr(fmt.Errorf("ioctl errno: %d", errno))
}
err = unix.SetNonblock(nfd, true)
fd := os.NewFile(uintptr(nfd), tunDevice)
checkErr(err)
for {
buf := make([]byte, 1500)
_, err := fd.Read(buf)
if err != nil {
fmt.Printf("read error: %v\n", err)
continue
}
fmt.Println("received packet")
switch buf[0] & 0xF0 {
case 0x40:
fmt.Println("received ipv4")
fmt.Printf("Length: %d\n", binary.BigEndian.Uint16(buf[2:4]))
fmt.Printf("Protocol: %d (1=ICMP, 6=TCP, 17=UDP)\n", buf[9])
fmt.Printf("Source IP: %s\n", net.IP(buf[12:16]))
fmt.Printf("Destination IP: %s\n", net.IP(buf[16:20]))
case 0x60:
fmt.Println("received ipv6")
fmt.Printf("Length: %d\n", binary.BigEndian.Uint16(buf[4:6]))
fmt.Printf("Protocol: %d (1=ICMP, 6=TCP, 17=UDP)\n", buf[7])
fmt.Printf("Source IP: %s\n", net.IP(buf[8:24]))
fmt.Printf("Destination IP: %s\n", net.IP(buf[24:40]))
}
}
}
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