Feature: add dhcp type dns client (#1509)

component/dhcp/conn.go

@@ -0,0 +1,18 @@
+package dhcp
+
+import (
+	"context"
+	"net"
+	"runtime"
+
+	"github.com/Dreamacro/clash/component/dialer"
+)
+
+func ListenDHCPClient(ctx context.Context, ifaceName string) (net.PacketConn, error) {
+	listenAddr := "0.0.0.0:68"
+	if runtime.GOOS == "linux" || runtime.GOOS == "android" {
+		listenAddr = "255.255.255.255:68"
+	}
+
+	return dialer.ListenPacket(ctx, "udp4", listenAddr, dialer.WithInterface(ifaceName), dialer.WithAddrReuse(true))
+}

component/dhcp/dhcp.go

@@ -0,0 +1,94 @@
+package dhcp
+
+import (
+	"context"
+	"errors"
+	"math/rand"
+	"net"
+
+	"github.com/insomniacslk/dhcp/dhcpv4"
+)
+
+var (
+	ErrNotResponding = errors.New("DHCP not responding")
+	ErrNotFound      = errors.New("DNS option not found")
+)
+
+func ResolveDNSFromDHCP(context context.Context, ifaceName string) ([]net.IP, error) {
+	conn, err := ListenDHCPClient(context, ifaceName)
+	if err != nil {
+		return nil, err
+	}
+	defer conn.Close()
+
+	result := make(chan []net.IP, 1)
+
+	discovery, err := dhcpv4.NewDiscovery(randomHardware(), dhcpv4.WithBroadcast(true), dhcpv4.WithRequestedOptions(dhcpv4.OptionDomainNameServer))
+	if err != nil {
+		return nil, err
+	}
+
+	go receiveOffer(conn, discovery.TransactionID, result)
+
+	_, err = conn.WriteTo(discovery.ToBytes(), &net.UDPAddr{IP: net.IPv4bcast, Port: 67})
+	if err != nil {
+		return nil, err
+	}
+
+	select {
+	case r, ok := <-result:
+		if !ok {
+			return nil, ErrNotFound
+		}
+		return r, nil
+	case <-context.Done():
+		return nil, ErrNotResponding
+	}
+}
+
+func receiveOffer(conn net.PacketConn, id dhcpv4.TransactionID, result chan<- []net.IP) {
+	defer close(result)
+
+	buf := make([]byte, dhcpv4.MaxMessageSize)
+
+	for {
+		n, _, err := conn.ReadFrom(buf)
+		if err != nil {
+			return
+		}
+
+		pkt, err := dhcpv4.FromBytes(buf[:n])
+		if err != nil {
+			continue
+		}
+
+		if pkt.MessageType() != dhcpv4.MessageTypeOffer {
+			continue
+		}
+
+		if pkt.TransactionID != id {
+			continue
+		}
+
+		dns := pkt.DNS()
+		if len(dns) == 0 {
+			return
+		}
+
+		result <- dns
+
+		return
+	}
+}
+
+func randomHardware() net.HardwareAddr {
+	addr := make(net.HardwareAddr, 6)
+
+	addr[0] = 0xff
+
+	for i := 1; i < len(addr); i++ {
+		addr[i] = byte(rand.Intn(254) + 1)
+	}
+
+	return addr
+}

component/dialer/bind.go

@@ -1,118 +0,0 @@
-package dialer
-
-import (
-	"errors"
-	"net"
-	"time"
-
-	"github.com/Dreamacro/clash/common/singledo"
-)
-
-// In some OS, such as Windows, it takes a little longer to get interface information
-var ifaceSingle = singledo.NewSingle(time.Second * 20)
-
-var (
-	errPlatformNotSupport = errors.New("unsupport platform")
-)
-
-func lookupTCPAddr(ip net.IP, addrs []net.Addr) (*net.TCPAddr, error) {
-	ipv4 := ip.To4() != nil
-
-	for _, elm := range addrs {
-		addr, ok := elm.(*net.IPNet)
-		if !ok {
-			continue
-		}
-
-		addrV4 := addr.IP.To4() != nil
-
-		if addrV4 && ipv4 {
-			return &net.TCPAddr{IP: addr.IP, Port: 0}, nil
-		} else if !addrV4 && !ipv4 {
-			return &net.TCPAddr{IP: addr.IP, Port: 0}, nil
-		}
-	}
-
-	return nil, ErrAddrNotFound
-}
-
-func lookupUDPAddr(ip net.IP, addrs []net.Addr) (*net.UDPAddr, error) {
-	ipv4 := ip.To4() != nil
-
-	for _, elm := range addrs {
-		addr, ok := elm.(*net.IPNet)
-		if !ok {
-			continue
-		}
-
-		addrV4 := addr.IP.To4() != nil
-
-		if addrV4 && ipv4 {
-			return &net.UDPAddr{IP: addr.IP, Port: 0}, nil
-		} else if !addrV4 && !ipv4 {
-			return &net.UDPAddr{IP: addr.IP, Port: 0}, nil
-		}
-	}
-
-	return nil, ErrAddrNotFound
-}
-
-func fallbackBindToDialer(dialer *net.Dialer, network string, ip net.IP, name string) error {
-	if !ip.IsGlobalUnicast() {
-		return nil
-	}
-
-	iface, err, _ := ifaceSingle.Do(func() (interface{}, error) {
-		return net.InterfaceByName(name)
-	})
-	if err != nil {
-		return err
-	}
-
-	addrs, err := iface.(*net.Interface).Addrs()
-	if err != nil {
-		return err
-	}
-
-	switch network {
-	case "tcp", "tcp4", "tcp6":
-		if addr, err := lookupTCPAddr(ip, addrs); err == nil {
-			dialer.LocalAddr = addr
-		} else {
-			return err
-		}
-	case "udp", "udp4", "udp6":
-		if addr, err := lookupUDPAddr(ip, addrs); err == nil {
-			dialer.LocalAddr = addr
-		} else {
-			return err
-		}
-	}
-
-	return nil
-}
-
-func fallbackBindToListenConfig(name string) (string, error) {
-	iface, err, _ := ifaceSingle.Do(func() (interface{}, error) {
-		return net.InterfaceByName(name)
-	})
-	if err != nil {
-		return "", err
-	}
-
-	addrs, err := iface.(*net.Interface).Addrs()
-	if err != nil {
-		return "", err
-	}
-
-	for _, elm := range addrs {
-		addr, ok := elm.(*net.IPNet)
-		if !ok || addr.IP.To4() == nil {
-			continue
-		}
-
-		return net.JoinHostPort(addr.IP.String(), "0"), nil
-	}
-
-	return "", ErrAddrNotFound
-}

component/dialer/bind_darwin.go

@@ -3,51 +3,57 @@ package dialer
 import (
 	"net"
 	"syscall"
+
+	"golang.org/x/sys/unix"
+
+	"github.com/Dreamacro/clash/component/iface"
 )
 
 type controlFn = func(network, address string, c syscall.RawConn) error
 
-func bindControl(ifaceIdx int) controlFn {
-	return func(network, address string, c syscall.RawConn) error {
+func bindControl(ifaceIdx int, chain controlFn) controlFn {
+	return func(network, address string, c syscall.RawConn) (err error) {
+		defer func() {
+			if err == nil && chain != nil {
+				err = chain(network, address, c)
+			}
+		}()
+
 		ipStr, _, err := net.SplitHostPort(address)
 		if err == nil {
 			ip := net.ParseIP(ipStr)
 			if ip != nil && !ip.IsGlobalUnicast() {
-				return nil
+				return
 			}
 		}
 
 		return c.Control(func(fd uintptr) {
 			switch network {
 			case "tcp4", "udp4":
-				syscall.SetsockoptInt(int(fd), syscall.IPPROTO_IP, syscall.IP_BOUND_IF, ifaceIdx)
+				unix.SetsockoptInt(int(fd), unix.IPPROTO_IP, unix.IP_BOUND_IF, ifaceIdx)
 			case "tcp6", "udp6":
-				syscall.SetsockoptInt(int(fd), syscall.IPPROTO_IPV6, syscall.IPV6_BOUND_IF, ifaceIdx)
+				unix.SetsockoptInt(int(fd), unix.IPPROTO_IPV6, unix.IPV6_BOUND_IF, ifaceIdx)
 			}
 		})
 	}
 }
 
-func bindIfaceToDialer(dialer *net.Dialer, ifaceName string) error {
-	iface, err, _ := ifaceSingle.Do(func() (interface{}, error) {
-		return net.InterfaceByName(ifaceName)
-	})
+func bindIfaceToDialer(ifaceName string, dialer *net.Dialer, _ string, _ net.IP) error {
+	ifaceObj, err := iface.ResolveInterface(ifaceName)
 	if err != nil {
 		return err
 	}
 
-	dialer.Control = bindControl(iface.(*net.Interface).Index)
+	dialer.Control = bindControl(ifaceObj.Index, dialer.Control)
 	return nil
 }
 
-func bindIfaceToListenConfig(lc *net.ListenConfig, ifaceName string) error {
-	iface, err, _ := ifaceSingle.Do(func() (interface{}, error) {
-		return net.InterfaceByName(ifaceName)
-	})
+func bindIfaceToListenConfig(ifaceName string, lc *net.ListenConfig, _, address string) (string, error) {
+	ifaceObj, err := iface.ResolveInterface(ifaceName)
 	if err != nil {
-		return err
+		return "", err
 	}
 
-	lc.Control = bindControl(iface.(*net.Interface).Index)
-	return nil
+	lc.Control = bindControl(ifaceObj.Index, lc.Control)
+	return address, nil
 }

component/dialer/bind_linux.go

@@ -3,34 +3,42 @@ package dialer
 import (
 	"net"
 	"syscall"
+
+	"golang.org/x/sys/unix"
 )
 
 type controlFn = func(network, address string, c syscall.RawConn) error
 
-func bindControl(ifaceName string) controlFn {
-	return func(network, address string, c syscall.RawConn) error {
+func bindControl(ifaceName string, chain controlFn) controlFn {
+	return func(network, address string, c syscall.RawConn) (err error) {
+		defer func() {
+			if err == nil && chain != nil {
+				err = chain(network, address, c)
+			}
+		}()
+
 		ipStr, _, err := net.SplitHostPort(address)
 		if err == nil {
 			ip := net.ParseIP(ipStr)
 			if ip != nil && !ip.IsGlobalUnicast() {
-				return nil
+				return
 			}
 		}
 
 		return c.Control(func(fd uintptr) {
-			syscall.BindToDevice(int(fd), ifaceName)
+			unix.BindToDevice(int(fd), ifaceName)
 		})
 	}
 }
 
-func bindIfaceToDialer(dialer *net.Dialer, ifaceName string) error {
-	dialer.Control = bindControl(ifaceName)
+func bindIfaceToDialer(ifaceName string, dialer *net.Dialer, _ string, _ net.IP) error {
+	dialer.Control = bindControl(ifaceName, dialer.Control)
 
 	return nil
 }
 
-func bindIfaceToListenConfig(lc *net.ListenConfig, ifaceName string) error {
-	lc.Control = bindControl(ifaceName)
+func bindIfaceToListenConfig(ifaceName string, lc *net.ListenConfig, _, address string) (string, error) {
+	lc.Control = bindControl(ifaceName, lc.Control)
 
-	return nil
+	return address, nil
 }

component/dialer/bind_others.go

@@ -3,12 +3,91 @@
 
 package dialer
 
-import "net"
+import (
+	"net"
+	"strconv"
+	"strings"
 
-func bindIfaceToDialer(dialer *net.Dialer, ifaceName string) error {
-	return errPlatformNotSupport
+	"github.com/Dreamacro/clash/component/iface"
+)
+
+func lookupLocalAddr(ifaceName string, network string, destination net.IP, port int) (net.Addr, error) {
+	ifaceObj, err := iface.ResolveInterface(ifaceName)
+	if err != nil {
+		return nil, err
+	}
+
+	var addr *net.IPNet
+	switch network {
+	case "udp4", "tcp4":
+		addr, err = ifaceObj.PickIPv4Addr(destination)
+	case "tcp6", "udp6":
+		addr, err = ifaceObj.PickIPv6Addr(destination)
+	default:
+		if destination != nil {
+			if destination.To4() != nil {
+				addr, err = ifaceObj.PickIPv4Addr(destination)
+			} else {
+				addr, err = ifaceObj.PickIPv6Addr(destination)
+			}
+		} else {
+			addr, err = ifaceObj.PickIPv4Addr(destination)
+		}
+	}
+	if err != nil {
+		return nil, err
+	}
+
+	if strings.HasPrefix(network, "tcp") {
+		return &net.TCPAddr{
+			IP:   addr.IP,
+			Port: port,
+		}, nil
+	} else if strings.HasPrefix(network, "udp") {
+		return &net.UDPAddr{
+			IP:   addr.IP,
+			Port: port,
+		}, nil
+	}
+
+	return nil, iface.ErrAddrNotFound
 }
 
-func bindIfaceToListenConfig(lc *net.ListenConfig, ifaceName string) error {
-	return errPlatformNotSupport
+func bindIfaceToDialer(ifaceName string, dialer *net.Dialer, network string, destination net.IP) error {
+	if !destination.IsGlobalUnicast() {
+		return nil
+	}
+
+	local := 0
+	if dialer.LocalAddr != nil {
+		_, port, err := net.SplitHostPort(dialer.LocalAddr.String())
+		if err == nil {
+			local, _ = strconv.Atoi(port)
+		}
+	}
+
+	addr, err := lookupLocalAddr(ifaceName, network, destination, local)
+	if err != nil {
+		return err
+	}
+
+	dialer.LocalAddr = addr
+
+	return nil
+}
+
+func bindIfaceToListenConfig(ifaceName string, _ *net.ListenConfig, network, address string) (string, error) {
+	_, port, err := net.SplitHostPort(address)
+	if err != nil {
+		port = "0"
+	}
+
+	local, _ := strconv.Atoi(port)
+
+	addr, err := lookupLocalAddr(ifaceName, network, nil, local)
+	if err != nil {
+		return "", err
+	}
+
+	return addr.String(), nil
 }

component/dialer/dialer.go

@@ -8,22 +8,7 @@ import (
 	"github.com/Dreamacro/clash/component/resolver"
 )
 
-func Dialer() (*net.Dialer, error) {
-	dialer := &net.Dialer{}
-	if DialerHook != nil {
-		if err := DialerHook(dialer); err != nil {
-			return nil, err
-		}
-	}
-
-	return dialer, nil
-}
-
-func Dial(network, address string) (net.Conn, error) {
-	return DialContext(context.Background(), network, address)
-}
-
-func DialContext(ctx context.Context, network, address string) (net.Conn, error) {
+func DialContext(ctx context.Context, network, address string, options ...Option) (net.Conn, error) {
 	switch network {
 	case "tcp4", "tcp6", "udp4", "udp6":
 		host, port, err := net.SplitHostPort(address)
@@ -31,11 +16,6 @@ func DialContext(ctx context.Context, network, address string) (net.Conn, error)
 			return nil, err
 		}
 
-		dialer, err := Dialer()
-		if err != nil {
-			return nil, err
-		}
-
 		var ip net.IP
 		switch network {
 		case "tcp4", "udp4":
@@ -43,38 +23,70 @@ func DialContext(ctx context.Context, network, address string) (net.Conn, error)
 		default:
 			ip, err = resolver.ResolveIPv6(host)
 		}
-
 		if err != nil {
 			return nil, err
 		}
 
-		if DialHook != nil {
-			if err := DialHook(dialer, network, ip); err != nil {
-				return nil, err
-			}
-		}
-		return dialer.DialContext(ctx, network, net.JoinHostPort(ip.String(), port))
+		return dialContext(ctx, network, ip, port, options)
 	case "tcp", "udp":
-		return dualStackDialContext(ctx, network, address)
+		return dualStackDialContext(ctx, network, address, options)
 	default:
 		return nil, errors.New("network invalid")
 	}
 }
 
-func ListenPacket(network, address string) (net.PacketConn, error) {
-	cfg := &net.ListenConfig{}
-	if ListenPacketHook != nil {
-		var err error
-		address, err = ListenPacketHook(cfg, address)
+func ListenPacket(ctx context.Context, network, address string, options ...Option) (net.PacketConn, error) {
+	cfg := &config{}
+
+	if !cfg.skipDefault {
+		for _, o := range DefaultOptions {
+			o(cfg)
+		}
+	}
+
+	for _, o := range options {
+		o(cfg)
+	}
+
+	lc := &net.ListenConfig{}
+	if cfg.interfaceName != "" {
+		addr, err := bindIfaceToListenConfig(cfg.interfaceName, lc, network, address)
 		if err != nil {
 			return nil, err
 		}
+		address = addr
+	}
+	if cfg.addrReuse {
+		addrReuseToListenConfig(lc)
+	}
+
+	return lc.ListenPacket(ctx, network, address)
+}
+
+func dialContext(ctx context.Context, network string, destination net.IP, port string, options []Option) (net.Conn, error) {
+	opt := &config{}
+
+	if !opt.skipDefault {
+		for _, o := range DefaultOptions {
+			o(opt)
+		}
+	}
+
+	for _, o := range options {
+		o(opt)
+	}
+
+	dialer := &net.Dialer{}
+	if opt.interfaceName != "" {
+		if err := bindIfaceToDialer(opt.interfaceName, dialer, network, destination); err != nil {
+			return nil, err
+		}
 	}
 
-	return cfg.ListenPacket(context.Background(), network, address)
+	return dialer.DialContext(ctx, network, net.JoinHostPort(destination.String(), port))
 }
 
-func dualStackDialContext(ctx context.Context, network, address string) (net.Conn, error) {
+func dualStackDialContext(ctx context.Context, network, address string, options []Option) (net.Conn, error) {
 	host, port, err := net.SplitHostPort(address)
 	if err != nil {
 		return nil, err
@@ -105,12 +117,6 @@ func dualStackDialContext(ctx context.Context, network, address string) (net.Con
 			}
 		}()
 
-		dialer, err := Dialer()
-		if err != nil {
-			result.error = err
-			return
-		}
-
 		var ip net.IP
 		if ipv6 {
 			ip, result.error = resolver.ResolveIPv6(host)
@@ -122,12 +128,7 @@ func dualStackDialContext(ctx context.Context, network, address string) (net.Con
 		}
 		result.resolved = true
 
-		if DialHook != nil {
-			if result.error = DialHook(dialer, network, ip); result.error != nil {
-				return
-			}
-		}
-		result.Conn, result.error = dialer.DialContext(ctx, network, net.JoinHostPort(ip.String(), port))
+		result.Conn, result.error = dialContext(ctx, network, ip, port, options)
 	}
 
 	go startRacer(ctx, network+"4", host, false)

component/dialer/hook.go

@@ -1,43 +0,0 @@
-package dialer
-
-import (
-	"errors"
-	"net"
-)
-
-type DialerHookFunc = func(dialer *net.Dialer) error
-type DialHookFunc = func(dialer *net.Dialer, network string, ip net.IP) error
-type ListenPacketHookFunc = func(lc *net.ListenConfig, address string) (string, error)
-
-var (
-	DialerHook       DialerHookFunc
-	DialHook         DialHookFunc
-	ListenPacketHook ListenPacketHookFunc
-)
-
-var (
-	ErrAddrNotFound      = errors.New("addr not found")
-	ErrNetworkNotSupport = errors.New("network not support")
-)
-
-func ListenPacketWithInterface(name string) ListenPacketHookFunc {
-	return func(lc *net.ListenConfig, address string) (string, error) {
-		err := bindIfaceToListenConfig(lc, name)
-		if err == errPlatformNotSupport {
-			address, err = fallbackBindToListenConfig(name)
-		}
-
-		return address, err
-	}
-}
-
-func DialerWithInterface(name string) DialHookFunc {
-	return func(dialer *net.Dialer, network string, ip net.IP) error {
-		err := bindIfaceToDialer(dialer, name)
-		if err == errPlatformNotSupport {
-			err = fallbackBindToDialer(dialer, network, ip, name)
-		}
-
-		return err
-	}
-}

component/dialer/options.go

@@ -0,0 +1,31 @@
+package dialer
+
+var (
+	DefaultOptions []Option
+)
+
+type config struct {
+	skipDefault   bool
+	interfaceName string
+	addrReuse     bool
+}
+
+type Option func(opt *config)
+
+func WithInterface(name string) Option {
+	return func(opt *config) {
+		opt.interfaceName = name
+	}
+}
+
+func WithAddrReuse(reuse bool) Option {
+	return func(opt *config) {
+		opt.addrReuse = reuse
+	}
+}
+
+func WithSkipDefault(skip bool) Option {
+	return func(opt *config) {
+		opt.skipDefault = skip
+	}
+}

component/dialer/reuse_others.go

@@ -0,0 +1,10 @@
+//go:build !darwin && !dragonfly && !freebsd && !linux && !netbsd && !openbsd && !solaris && !windows
+// +build !darwin,!dragonfly,!freebsd,!linux,!netbsd,!openbsd,!solaris,!windows
+
+package dialer
+
+import (
+	"net"
+)
+
+func addrReuseToListenConfig(*net.ListenConfig) {}

component/dialer/reuse_unix.go

@@ -0,0 +1,28 @@
+//go:build darwin || dragonfly || freebsd || linux || netbsd || openbsd || solaris
+// +build darwin dragonfly freebsd linux netbsd openbsd solaris
+
+package dialer
+
+import (
+	"net"
+	"syscall"
+
+	"golang.org/x/sys/unix"
+)
+
+func addrReuseToListenConfig(lc *net.ListenConfig) {
+	chain := lc.Control
+
+	lc.Control = func(network, address string, c syscall.RawConn) (err error) {
+		defer func() {
+			if err == nil && chain != nil {
+				err = chain(network, address, c)
+			}
+		}()
+
+		return c.Control(func(fd uintptr) {
+			unix.SetsockoptInt(int(fd), unix.SOL_SOCKET, unix.SO_REUSEADDR, 1)
+			unix.SetsockoptInt(int(fd), unix.SOL_SOCKET, unix.SO_REUSEPORT, 1)
+		})
+	}
+}

component/dialer/reuse_windows.go

@@ -0,0 +1,24 @@
+package dialer
+
+import (
+	"net"
+	"syscall"
+
+	"golang.org/x/sys/windows"
+)
+
+func addrReuseToListenConfig(lc *net.ListenConfig) {
+	chain := lc.Control
+
+	lc.Control = func(network, address string, c syscall.RawConn) (err error) {
+		defer func() {
+			if err == nil && chain != nil {
+				err = chain(network, address, c)
+			}
+		}()
+
+		return c.Control(func(fd uintptr) {
+			windows.SetsockoptInt(windows.Handle(fd), windows.SOL_SOCKET, windows.SO_REUSEADDR, 1)
+		})
+	}
+}

component/iface/iface.go

@@ -0,0 +1,113 @@
+package iface
+
+import (
+	"errors"
+	"net"
+	"time"
+
+	"github.com/Dreamacro/clash/common/singledo"
+)
+
+type Interface struct {
+	Index        int
+	Name         string
+	Addrs        []*net.IPNet
+	HardwareAddr net.HardwareAddr
+}
+
+var ErrIfaceNotFound = errors.New("interface not found")
+var ErrAddrNotFound = errors.New("addr not found")
+
+var interfaces = singledo.NewSingle(time.Second * 20)
+
+func ResolveInterface(name string) (*Interface, error) {
+	value, err, _ := interfaces.Do(func() (interface{}, error) {
+		ifaces, err := net.Interfaces()
+		if err != nil {
+			return nil, err
+		}
+
+		r := map[string]*Interface{}
+
+		for _, iface := range ifaces {
+			addrs, err := iface.Addrs()
+			if err != nil {
+				continue
+			}
+
+			ipNets := make([]*net.IPNet, 0, len(addrs))
+			for _, addr := range addrs {
+				ipNet := addr.(*net.IPNet)
+				if v4 := ipNet.IP.To4(); v4 != nil {
+					ipNet.IP = v4
+				}
+
+				ipNets = append(ipNets, ipNet)
+			}
+
+			r[iface.Name] = &Interface{
+				Index:        iface.Index,
+				Name:         iface.Name,
+				Addrs:        ipNets,
+				HardwareAddr: iface.HardwareAddr,
+			}
+		}
+
+		return r, nil
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	ifaces := value.(map[string]*Interface)
+	iface, ok := ifaces[name]
+	if !ok {
+		return nil, ErrIfaceNotFound
+	}
+
+	return iface, nil
+}
+
+func FlushCache() {
+	interfaces.Reset()
+}
+
+func (iface *Interface) PickIPv4Addr(destination net.IP) (*net.IPNet, error) {
+	return iface.pickIPAddr(destination, func(addr *net.IPNet) bool {
+		return addr.IP.To4() != nil
+	})
+}
+
+func (iface *Interface) PickIPv6Addr(destination net.IP) (*net.IPNet, error) {
+	return iface.pickIPAddr(destination, func(addr *net.IPNet) bool {
+		return addr.IP.To4() == nil
+	})
+}
+
+func (iface *Interface) pickIPAddr(destination net.IP, accept func(addr *net.IPNet) bool) (*net.IPNet, error) {
+	var fallback *net.IPNet
+
+	for _, addr := range iface.Addrs {
+		if !accept(addr) {
+			continue
+		}
+
+		if fallback == nil && !addr.IP.IsLinkLocalUnicast() {
+			fallback = addr
+
+			if destination == nil {
+				break
+			}
+		}
+
+		if destination != nil && addr.Contains(destination) {
+			return addr, nil
+		}
+	}
+
+	if fallback == nil {
+		return nil, ErrAddrNotFound
+	}
+
+	return fallback, nil
+}