76 lines
1.6 KiB
Go
76 lines
1.6 KiB
Go
//go:build linux
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package sdk
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import (
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"fmt"
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"syscall"
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"unsafe"
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)
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type tapInterface struct {
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Name string
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MTU int
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fd int
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}
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func openTap(name string, mtu int) (*tapInterface, error) {
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fd, err := syscall.Open("/dev/net/tun", syscall.O_RDWR, 0)
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if err != nil {
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return nil, fmt.Errorf("open /dev/net/tun: %w", err)
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}
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var ifr struct {
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name [16]byte
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flags uint16
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}
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copy(ifr.name[:], []byte(name))
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ifr.flags = 0x0002 | 0x1000 // IFF_TAP | IFF_NO_PI
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if _, _, errno := syscall.Syscall(syscall.SYS_IOCTL, uintptr(fd), 0x400454ca, uintptr(unsafe.Pointer(&ifr))); errno != 0 {
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syscall.Close(fd)
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return nil, fmt.Errorf("TUNSETIFF: %w", errno)
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}
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devName := string(ifr.name[:])
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if idx := indexOfZero(devName); idx >= 0 {
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devName = devName[:idx]
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}
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ti := &tapInterface{Name: devName, MTU: mtu, fd: fd}
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// Set MTU via socket ioctl
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s, err := syscall.Socket(syscall.AF_INET, syscall.SOCK_DGRAM, 0)
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if err == nil {
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defer syscall.Close(s)
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var mtuReq struct {
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name [16]byte
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mtu int32
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}
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copy(mtuReq.name[:], []byte(devName))
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mtuReq.mtu = int32(mtu)
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syscall.Syscall(syscall.SYS_IOCTL, uintptr(s), 0x400c4a52, uintptr(unsafe.Pointer(&mtuReq))) // SIOCSIFMTU
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}
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return ti, nil
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}
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func (ti *tapInterface) Read(buf []byte) (int, error) {
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return syscall.Read(ti.fd, buf)
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}
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func (ti *tapInterface) Write(buf []byte) error {
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_, err := syscall.Write(ti.fd, buf)
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return err
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}
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func (ti *tapInterface) Close() error {
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return syscall.Close(ti.fd)
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}
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func indexOfZero(s string) int {
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for i, c := range []byte(s) {
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if c == 0 {
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return i
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}
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}
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return -1
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}
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