add ARP; add tap internal calls; more lneto2 additions

internal/tap.go

@@ -0,0 +1,68 @@
+//go:build linux && !baremetal
+
+package internal
+
+import (
+	"errors"
+	"fmt"
+	"net/netip"
+	"os"
+	"os/exec"
+	"syscall"
+	"unsafe"
+)
+
+type Tap struct {
+	fd   int
+	name string
+}
+
+func NewTap(name string, ip netip.Prefix) (*Tap, error) {
+	if len(name) >= syscall.IFNAMSIZ {
+		return nil, errors.New("name too large")
+	}
+	fd, err := syscall.Open("/dev/net/tun", os.O_RDWR, 0777)
+	if err != nil {
+		return nil, fmt.Errorf("failed to open tun device: %w", err)
+	}
+
+	var ifr [syscall.IFNAMSIZ + 64]byte // extra space for compatibility
+
+	// Set the name; it will be zero-padded automatically.
+	copy(ifr[:syscall.IFNAMSIZ-1], name)
+
+	// Set the flags (starting at offset IFNAMSIZ).
+	flags := uint16(syscall.IFF_TAP | syscall.IFF_NO_PI)
+	*(*uint16)(unsafe.Pointer(&ifr[syscall.IFNAMSIZ])) = flags
+	// Issue the ioctl to create the interface.
+	_, _, errno := syscall.Syscall(syscall.SYS_IOCTL, uintptr(fd), uintptr(syscall.TUNSETIFF), uintptr(unsafe.Pointer(&ifr[0])))
+	if errno != 0 {
+		return nil, fmt.Errorf("creating tap interface: %w", errno)
+	}
+	if ip.IsValid() {
+		// Optionally, bring the interface up and assign an IP address.
+		// You can do this using the 'ip' command for simplicity.
+		err = exec.Command("ip", "link", "set", "dev", name, "up").Run()
+		if err != nil {
+			return nil, fmt.Errorf("failed to set ip link: %w", err)
+		}
+
+		err = exec.Command("ip", "addr", "add", ip.String(), "dev", name).Run()
+		if err != nil {
+			return nil, fmt.Errorf("failed to assign IP address: %w", err)
+		}
+	}
+	return &Tap{fd: fd, name: name}, nil
+}
+
+func (tap *Tap) Read(b []byte) (int, error) {
+	return syscall.Read(tap.fd, b)
+}
+
+func (tap *Tap) Write(b []byte) (int, error) {
+	return syscall.Write(tap.fd, b)
+}
+
+func (tap *Tap) Close() error {
+	return syscall.Close(tap.fd)
+}