feat: add Go SDK package (REST client + VL1 agent + TAP device)

sdk/tap_linux.go

@@ -0,0 +1,75 @@
+//go:build linux
+
+package sdk
+
+import (
+	"fmt"
+	"syscall"
+	"unsafe"
+)
+
+type tapInterface struct {
+	Name string
+	MTU  int
+	fd   int
+}
+
+func openTap(name string, mtu int) (*tapInterface, error) {
+	fd, err := syscall.Open("/dev/net/tun", syscall.O_RDWR, 0)
+	if err != nil {
+		return nil, fmt.Errorf("open /dev/net/tun: %w", err)
+	}
+	var ifr struct {
+		name  [16]byte
+		flags uint16
+	}
+	copy(ifr.name[:], []byte(name))
+	ifr.flags = 0x0002 | 0x1000 // IFF_TAP | IFF_NO_PI
+	if _, _, errno := syscall.Syscall(syscall.SYS_IOCTL, uintptr(fd), 0x400454ca, uintptr(unsafe.Pointer(&ifr))); errno != 0 {
+		syscall.Close(fd)
+		return nil, fmt.Errorf("TUNSETIFF: %w", errno)
+	}
+	devName := string(ifr.name[:])
+	if idx := indexOfZero(devName); idx >= 0 {
+		devName = devName[:idx]
+	}
+	ti := &tapInterface{Name: devName, MTU: mtu, fd: fd}
+
+	// Set MTU via socket ioctl
+	s, err := syscall.Socket(syscall.AF_INET, syscall.SOCK_DGRAM, 0)
+	if err == nil {
+		defer syscall.Close(s)
+		var mtuReq struct {
+			name [16]byte
+			mtu  int32
+		}
+		copy(mtuReq.name[:], []byte(devName))
+		mtuReq.mtu = int32(mtu)
+		syscall.Syscall(syscall.SYS_IOCTL, uintptr(s), 0x400c4a52, uintptr(unsafe.Pointer(&mtuReq))) // SIOCSIFMTU
+	}
+	return ti, nil
+}
+
+func (ti *tapInterface) Read(buf []byte) (int, error) {
+	return syscall.Read(ti.fd, buf)
+}
+
+func (ti *tapInterface) Write(buf []byte) error {
+	_, err := syscall.Write(ti.fd, buf)
+	return err
+}
+
+func (ti *tapInterface) Close() error {
+	return syscall.Close(ti.fd)
+}
+
+func indexOfZero(s string) int {
+	for i, c := range []byte(s) {
+		if c == 0 {
+			return i
+		}
+	}
+	return -1
+}
+
+