Set gateway for windows

tun.go

@@ -53,6 +53,8 @@ type Options struct {
 	MTU                      uint32
 	GSO                      bool
 	AutoRoute                bool
+	Inet4Gateway             netip.Addr
+	Inet6Gateway             netip.Addr
 	DNSServers               []netip.Addr
 	IPRoute2TableIndex       int
 	IPRoute2RuleIndex        int
@@ -82,6 +84,26 @@ type Options struct {
 	EXP_DisableDNSHijack bool
 }
 
+func (o *Options) Inet4GatewayAddr() netip.Addr {
+	if o.Inet4Gateway.IsValid() {
+		return o.Inet4Gateway
+	}
+	if len(o.Inet4Address) > 0 {
+		return o.Inet4Address[0].Addr()
+	}
+	return netip.IPv4Unspecified()
+}
+
+func (o *Options) Inet6GatewayAddr() netip.Addr {
+	if o.Inet6Gateway.IsValid() {
+		return o.Inet6Gateway
+	}
+	if len(o.Inet6Address) > 0 {
+		return o.Inet6Address[0].Addr()
+	}
+	return netip.IPv6Unspecified()
+}
+
 func CalculateInterfaceName(name string) (tunName string) {
 	if runtime.GOOS == "darwin" {
 		tunName = "utun"

tun_darwin.go

@@ -245,11 +245,12 @@ func configure(tunFd int, ifIndex int, name string, options Options) error {
 		if err != nil {
 			return err
 		}
+		gateway4, gateway6 := options.Inet4GatewayAddr(), options.Inet6GatewayAddr()
 		for _, routeRange := range routeRanges {
 			if routeRange.Addr().Is4() {
-				err = addRoute(routeRange, options.Inet4Address[0].Addr())
+				err = addRoute(routeRange, gateway4)
 			} else {
-				err = addRoute(routeRange, options.Inet6Address[0].Addr())
+				err = addRoute(routeRange, gateway6)
 			}
 			if err != nil {
 				return E.Cause(err, "add route: ", routeRange)

tun_linux.go

@@ -350,9 +350,26 @@ func (t *NativeTun) routes(tunLink netlink.Link) ([]netlink.Route, error) {
 	if err != nil {
 		return nil, err
 	}
+	// Do not create gateway on linux by default
+	var (
+		gateway4, gateway6 netip.Addr
+	)
+	if t.options.Inet4Gateway.IsValid() {
+		gateway4 = t.options.Inet4Gateway
+	}
+	if t.options.Inet6Gateway.IsValid() {
+		gateway6 = t.options.Inet6Gateway
+	}
 	return common.Map(routeRanges, func(it netip.Prefix) netlink.Route {
+		var gateway net.IP
+		if it.Addr().Is4() && gateway4.IsValid() {
+			gateway = gateway4.AsSlice()
+		} else if it.Addr().Is6() && gateway6.IsValid() {
+			gateway = gateway6.AsSlice()
+		}
 		return netlink.Route{
 			Dst:       prefixToIPNet(it),
+			Gw:        gateway,
 			LinkIndex: tunLink.Attrs().Index,
 			Table:     t.options.IPRoute2TableIndex,
 		}

tun_windows.go

@@ -103,15 +103,16 @@ func (t *NativeTun) configure() error {
 		_ = luid.DisableDNSRegistration()
 	}
 	if t.options.AutoRoute {
+		gateway4, gateway6 := t.options.Inet4GatewayAddr(), t.options.Inet6GatewayAddr()
 		routeRanges, err := t.options.BuildAutoRouteRanges(false)
 		if err != nil {
 			return err
 		}
 		for _, routeRange := range routeRanges {
 			if routeRange.Addr().Is4() {
-				err = luid.AddRoute(routeRange, netip.IPv4Unspecified(), 0)
+				err = luid.AddRoute(routeRange, gateway4, 0)
 			} else {
-				err = luid.AddRoute(routeRange, netip.IPv6Unspecified(), 0)
+				err = luid.AddRoute(routeRange, gateway6, 0)
 			}
 		}
 		if err != nil {