init

internal/tun/tun.go

@@ -0,0 +1,29 @@
+// Package tun provides a cross-platform TUN virtual network card
+// abstraction. Each platform implements the Device interface.
+//
+// On macOS the TUN device is a utunN interface created via the
+// songgao/water library (same as the server). Configuration uses
+// ifconfig/route commands and requires root privileges.
+package tun
+
+import "net"
+
+// Device represents a TUN virtual network interface.
+type Device interface {
+	// Name returns the OS-assigned interface name (e.g. utun4).
+	Name() string
+	// Read reads one IP packet from the TUN device.
+	Read(p []byte) (int, error)
+	// Write writes one IP packet to the TUN device.
+	Write(p []byte) (int, error)
+	// Configure sets the interface address, prefix, and peer IP.
+	Configure(localIP net.IP, prefix int, peerIP net.IP) error
+	// SetMTU sets the interface MTU.
+	SetMTU(mtu int) error
+	// Close destroys the TUN device.
+	Close() error
+}
+
+// Create creates a new TUN device. If name is empty, the OS assigns
+// a name (utunN on macOS, tunN on Linux).
+func Create(name string) (Device, error) { return createTUN(name) }

internal/tun/tun_darwin.go

@@ -0,0 +1,60 @@
+//go:build darwin
+
+package tun
+
+import (
+	"fmt"
+	"net"
+	"os"
+	"os/exec"
+	"strings"
+
+	"github.com/songgao/water"
+)
+
+type darwinDevice struct {
+	ifce *water.Interface
+}
+
+func createTUN(name string) (Device, error) {
+	cfg := water.Config{DeviceType: water.TUN}
+	cfg.Name = name
+	ifce, err := water.New(cfg)
+	if err != nil {
+		return nil, fmt.Errorf("create utun: %w", err)
+	}
+	return &darwinDevice{ifce: ifce}, nil
+}
+
+func (d *darwinDevice) Name() string                  { return d.ifce.Name() }
+func (d *darwinDevice) Read(p []byte) (int, error)    { return d.ifce.Read(p) }
+func (d *darwinDevice) Write(p []byte) (int, error)   { return d.ifce.Write(p) }
+func (d *darwinDevice) Close() error                  { return d.ifce.Close() }
+
+func (d *darwinDevice) Configure(localIP net.IP, prefix int, peerIP net.IP) error {
+	if localIP == nil {
+		return execCmd("ifconfig", d.Name(), "up")
+	}
+	inetType := "inet"
+	if localIP.To4() == nil {
+		inetType = "inet6"
+	}
+	localCidr := fmt.Sprintf("%s/%d", localIP.String(), prefix)
+	// ifconfig utunN inet <ip>/<prefix> <peer_ip> up
+	return execCmd("ifconfig", d.Name(), inetType, localCidr, peerIP.String(), "up")
+}
+
+func (d *darwinDevice) SetMTU(mtu int) error {
+	return execCmd("ifconfig", d.Name(), "mtu", fmt.Sprintf("%d", mtu))
+}
+
+// execCmd runs a command, forwarding stdout/stderr.
+func execCmd(name string, arg ...string) error {
+	cmd := exec.Command(name, arg...)
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+	if err := cmd.Run(); err != nil {
+		return fmt.Errorf("%s %s: %w", name, strings.Join(arg, " "), err)
+	}
+	return nil
+}

internal/tun/tun_linux.go

@@ -0,0 +1,61 @@
+//go:build !darwin
+
+package tun
+
+import (
+	"fmt"
+	"net"
+	"os"
+	"os/exec"
+	"strings"
+
+	"github.com/songgao/water"
+)
+
+type linuxDevice struct {
+	ifce *water.Interface
+}
+
+func createTUN(name string) (Device, error) {
+	cfg := water.Config{DeviceType: water.TUN}
+	cfg.Name = name
+	ifce, err := water.New(cfg)
+	if err != nil {
+		return nil, fmt.Errorf("create tun: %w", err)
+	}
+	return &linuxDevice{ifce: ifce}, nil
+}
+
+func (d *linuxDevice) Name() string                { return d.ifce.Name() }
+func (d *linuxDevice) Read(p []byte) (int, error)  { return d.ifce.Read(p) }
+func (d *linuxDevice) Write(p []byte) (int, error) { return d.ifce.Write(p) }
+func (d *linuxDevice) Close() error                { return d.ifce.Close() }
+
+func (d *linuxDevice) Configure(localIP net.IP, prefix int, peerIP net.IP) error {
+	if err := execCmd("ip", "link", "set", "dev", d.Name(), "up"); err != nil {
+		return err
+	}
+	if localIP == nil {
+		return nil
+	}
+	localCidr := fmt.Sprintf("%s/%d", localIP.String(), prefix)
+	if err := execCmd("ip", "addr", "add", "dev", d.Name(), localCidr, "peer", peerIP.String()); err != nil {
+		// Fall back without peer (some kernels).
+		return execCmd("ip", "addr", "add", "dev", d.Name(), localCidr)
+	}
+	return nil
+}
+
+func (d *linuxDevice) SetMTU(mtu int) error {
+	return execCmd("ip", "link", "set", "dev", d.Name(), "mtu", fmt.Sprintf("%d", mtu))
+}
+
+func execCmd(name string, arg ...string) error {
+	cmd := exec.Command(name, arg...)
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+	if err := cmd.Run(); err != nil {
+		return fmt.Errorf("%s %s: %w", name, strings.Join(arg, " "), err)
+	}
+	return nil
+}