feat(wip): DirectOutbound bind to device

extras/outbounds/ob_direct.go

@@ -4,6 +4,7 @@ import (
 	"errors"
 	"net"
 	"strconv"
+	"time"
 )
 
 type DirectOutboundMode int
@@ -14,22 +15,34 @@ const (
 	DirectOutboundMode46                             // Use IPv4 address when available, otherwise IPv6
 	DirectOutboundMode6                              // Use IPv6 only, fail if not available
 	DirectOutboundMode4                              // Use IPv4 only, fail if not available
+
+	defaultDialerTimeout = 10 * time.Second
 )
 
-var _ PluggableOutbound = (*DirectOutbound)(nil)
-
-// DirectOutbound is a PluggableOutbound that connects directly to the target
+// directOutbound is a PluggableOutbound that connects directly to the target
 // using the local network (as opposed to using a proxy, for example).
 // It prefers to use ResolveInfo in AddrEx if available. But if it's nil,
 // it will fall back to resolving Host using Go's built-in DNS resolver.
-type DirectOutbound struct {
-	Mode   DirectOutboundMode
-	Dialer *net.Dialer
+type directOutbound struct {
+	Mode       DirectOutboundMode
+	Dialer     *net.Dialer
+	DeviceName string // For UDP binding
+}
+
+// NewDirectOutboundSimple creates a new directOutbound with the given mode,
+// without binding to a specific device. Works on all platforms.
+func NewDirectOutboundSimple(mode DirectOutboundMode) PluggableOutbound {
+	return &directOutbound{
+		Mode: mode,
+		Dialer: &net.Dialer{
+			Timeout: defaultDialerTimeout,
+		},
+	}
 }
 
 // resolve is our built-in DNS resolver for handling the case when
 // AddrEx.ResolveInfo is nil.
-func (d *DirectOutbound) resolve(reqAddr *AddrEx) {
+func (d *directOutbound) resolve(reqAddr *AddrEx) {
 	ips, err := net.LookupIP(reqAddr.Host)
 	if err != nil {
 		reqAddr.ResolveInfo = &ResolveInfo{Err: err}
@@ -52,7 +65,7 @@ func (d *DirectOutbound) resolve(reqAddr *AddrEx) {
 	reqAddr.ResolveInfo = r
 }
 
-func (d *DirectOutbound) DialTCP(reqAddr *AddrEx) (net.Conn, error) {
+func (d *directOutbound) DialTCP(reqAddr *AddrEx) (net.Conn, error) {
 	if reqAddr.ResolveInfo == nil {
 		// AddrEx.ResolveInfo is nil (no resolver in the pipeline),
 		// we need to resolve the address ourselves.
@@ -103,7 +116,7 @@ func (d *DirectOutbound) DialTCP(reqAddr *AddrEx) (net.Conn, error) {
 	}
 }
 
-func (d *DirectOutbound) dialTCP(ip net.IP, port uint16) (net.Conn, error) {
+func (d *directOutbound) dialTCP(ip net.IP, port uint16) (net.Conn, error) {
 	return d.Dialer.Dial("tcp", net.JoinHostPort(ip.String(), strconv.Itoa(int(port))))
 }
 
@@ -115,7 +128,7 @@ type dialResult struct {
 // dualStackDialTCP dials the target using both IPv4 and IPv6 addresses simultaneously.
 // It returns the first successful connection and drops the other one.
 // If both connections fail, it returns the last error.
-func (d *DirectOutbound) dualStackDialTCP(ipv4, ipv6 net.IP, port uint16) (net.Conn, error) {
+func (d *directOutbound) dualStackDialTCP(ipv4, ipv6 net.IP, port uint16) (net.Conn, error) {
 	ch := make(chan dialResult, 2)
 	go func() {
 		conn, err := d.dialTCP(ipv4, port)
@@ -143,7 +156,7 @@ func (d *DirectOutbound) dualStackDialTCP(ipv4, ipv6 net.IP, port uint16) (net.C
 }
 
 type directOutboundUDPConn struct {
-	*DirectOutbound
+	*directOutbound
 	*net.UDPConn
 }
 
@@ -163,13 +176,13 @@ func (u *directOutboundUDPConn) WriteTo(b []byte, addr *AddrEx) (int, error) {
 	if addr.ResolveInfo == nil {
 		// Although practically rare, it is possible to send
 		// UDP packets to a hostname (instead of an IP address).
-		u.DirectOutbound.resolve(addr)
+		u.directOutbound.resolve(addr)
 	}
 	r := addr.ResolveInfo
 	if r.IPv4 == nil && r.IPv6 == nil {
 		return 0, r.Err
 	}
-	switch u.DirectOutbound.Mode {
+	switch u.directOutbound.Mode {
 	case DirectOutboundModeAuto:
 		// This is a special case.
 		// It's not possible to do a "dual stack race dial" for UDP,
@@ -237,13 +250,20 @@ func (u *directOutboundUDPConn) Close() error {
 	return u.UDPConn.Close()
 }
 
-func (d *DirectOutbound) ListenUDP() (UDPConn, error) {
+func (d *directOutbound) ListenUDP() (UDPConn, error) {
 	c, err := net.ListenUDP("udp", nil)
 	if err != nil {
 		return nil, err
 	}
+	if d.DeviceName != "" {
+		if err := udpConnBindToDevice(c, d.DeviceName); err != nil {
+			// Don't forget to close the UDPConn if binding fails
+			_ = c.Close()
+			return nil, err
+		}
+	}
 	return &directOutboundUDPConn{
-		DirectOutbound: d,
+		directOutbound: d,
 		UDPConn:        c,
 	}, nil
 }

extras/outbounds/ob_direct_linux.go

@@ -0,0 +1,55 @@
+package outbounds
+
+import (
+	"errors"
+	"net"
+	"syscall"
+)
+
+// NewDirectOutboundBindToDevice creates a new directOutbound with the given mode,
+// and binds to the given device. Only works on Linux.
+func NewDirectOutboundBindToDevice(mode DirectOutboundMode, deviceName string) (PluggableOutbound, error) {
+	if err := verifyDeviceName(deviceName); err != nil {
+		return nil, err
+	}
+	return &directOutbound{
+		Mode: mode,
+		Dialer: &net.Dialer{
+			Timeout: defaultDialerTimeout,
+			Control: func(network, address string, c syscall.RawConn) error {
+				var errBind error
+				err := c.Control(func(fd uintptr) {
+					errBind = syscall.BindToDevice(int(fd), deviceName)
+				})
+				if err != nil {
+					return err
+				}
+				return errBind
+			},
+		},
+		DeviceName: deviceName,
+	}, nil
+}
+
+func verifyDeviceName(deviceName string) error {
+	if deviceName == "" {
+		return errors.New("device name cannot be empty")
+	}
+	_, err := net.InterfaceByName(deviceName)
+	return err
+}
+
+func udpConnBindToDevice(conn *net.UDPConn, deviceName string) error {
+	sc, err := conn.SyscallConn()
+	if err != nil {
+		return err
+	}
+	var errBind error
+	err = sc.Control(func(fd uintptr) {
+		errBind = syscall.BindToDevice(int(fd), deviceName)
+	})
+	if err != nil {
+		return err
+	}
+	return errBind
+}

extras/outbounds/ob_direct_others.go

@@ -0,0 +1,19 @@
+//go:build !linux
+
+package outbounds
+
+import (
+	"errors"
+	"net"
+)
+
+// NewDirectOutboundBindToDevice creates a new directOutbound with the given mode,
+// and binds to the given device. This doesn't work on non-Linux platforms, so this
+// is just a stub function that always returns an error.
+func NewDirectOutboundBindToDevice(mode DirectOutboundMode, deviceName string) (PluggableOutbound, error) {
+	return nil, errors.New("binding to device is not supported on this platform")
+}
+
+func udpConnBindToDevice(conn *net.UDPConn, deviceName string) error {
+	return errors.New("binding to device is not supported on this platform")
+}