virtual-net: initial (#4751)

pkg/vnet/tun_darwin.go

@@ -0,0 +1,85 @@
+// Copyright 2025 The frp Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package vnet
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"os/exec"
+
+	"golang.zx2c4.com/wireguard/tun"
+)
+
+const (
+	defaultTunName = "utun"
+	defaultMTU     = 1420
+)
+
+func openTun(_ context.Context, addr string) (tun.Device, error) {
+	dev, err := tun.CreateTUN(defaultTunName, defaultMTU)
+	if err != nil {
+		return nil, err
+	}
+
+	name, err := dev.Name()
+	if err != nil {
+		return nil, err
+	}
+
+	ip, ipNet, err := net.ParseCIDR(addr)
+	if err != nil {
+		return nil, err
+	}
+
+	// Calculate a peer IP for the point-to-point tunnel
+	peerIP := generatePeerIP(ip)
+
+	// Configure the interface with proper point-to-point addressing
+	if err = exec.Command("ifconfig", name, "inet", ip.String(), peerIP.String(), "mtu", fmt.Sprint(defaultMTU), "up").Run(); err != nil {
+		return nil, err
+	}
+
+	// Add default route for the tunnel subnet
+	routes := []net.IPNet{*ipNet}
+	if err = addRoutes(name, routes); err != nil {
+		return nil, err
+	}
+	return dev, nil
+}
+
+// generatePeerIP creates a peer IP for the point-to-point tunnel
+// by incrementing the last octet of the IP
+func generatePeerIP(ip net.IP) net.IP {
+	// Make a copy to avoid modifying the original
+	peerIP := make(net.IP, len(ip))
+	copy(peerIP, ip)
+
+	// Increment the last octet
+	peerIP[len(peerIP)-1]++
+
+	return peerIP
+}
+
+// addRoutes configures system routes for the TUN interface
+func addRoutes(ifName string, routes []net.IPNet) error {
+	for _, route := range routes {
+		routeStr := route.String()
+		if err := exec.Command("route", "add", "-net", routeStr, "-interface", ifName).Run(); err != nil {
+			return err
+		}
+	}
+	return nil
+}