Add auto_route and auto_detect_interface for linux

common/dialer/auto_linux.go

@@ -0,0 +1,23 @@
+package dialer
+
+import (
+	"syscall"
+
+	"github.com/sagernet/sing-box/adapter"
+	"github.com/sagernet/sing/common/control"
+	E "github.com/sagernet/sing/common/exceptions"
+)
+
+func BindToInterface(router adapter.Router) control.Func {
+	return func(network, address string, conn syscall.RawConn) error {
+		interfaceName := router.DefaultInterfaceName()
+		if interfaceName == "" {
+			return nil
+		}
+		var innerErr error
+		err := conn.Control(func(fd uintptr) {
+			innerErr = syscall.BindToDevice(int(fd), interfaceName)
+		})
+		return E.Errors(innerErr, err)
+	}
+}

common/dialer/auto_other.go

@@ -0,0 +1,12 @@
+//go:build !linux
+
+package dialer
+
+import (
+	"github.com/sagernet/sing-box/adapter"
+	"github.com/sagernet/sing/common/control"
+)
+
+func BindToInterface(router adapter.Router) control.Func {
+	return nil
+}

common/dialer/default.go

@@ -5,6 +5,7 @@ import (
 	"net"
 	"time"
 
+	"github.com/sagernet/sing-box/adapter"
 	C "github.com/sagernet/sing-box/constant"
 	"github.com/sagernet/sing-box/option"
 	"github.com/sagernet/sing/common/control"
@@ -18,12 +19,15 @@ type DefaultDialer struct {
 	net.ListenConfig
 }
 
-func NewDefault(options option.DialerOptions) *DefaultDialer {
+func NewDefault(router adapter.Router, options option.DialerOptions) *DefaultDialer {
 	var dialer net.Dialer
 	var listener net.ListenConfig
 	if options.BindInterface != "" {
 		dialer.Control = control.Append(dialer.Control, control.BindToInterface(options.BindInterface))
 		listener.Control = control.Append(listener.Control, control.BindToInterface(options.BindInterface))
+	} else if router.AutoDetectInterface() {
+		dialer.Control = BindToInterface(router)
+		listener.Control = BindToInterface(router)
 	}
 	if options.RoutingMark != 0 {
 		dialer.Control = control.Append(dialer.Control, control.RoutingMark(options.RoutingMark))

common/dialer/dialer.go

@@ -12,7 +12,7 @@ import (
 
 func New(router adapter.Router, options option.DialerOptions) N.Dialer {
 	if options.Detour == "" {
-		return NewDefault(options)
+		return NewDefault(router, options)
 	} else {
 		return NewDetour(router, options.Detour)
 	}

common/iffmonitor/monitor.go

@@ -0,0 +1,9 @@
+package iffmonitor
+
+import "github.com/sagernet/sing-box/adapter"
+
+type InterfaceMonitor interface {
+	adapter.Service
+	DefaultInterfaceName() string
+	DefaultInterfaceIndex() int
+}

common/iffmonitor/monitor_linux.go

@@ -0,0 +1,100 @@
+package iffmonitor
+
+import (
+	"os"
+
+	"github.com/sagernet/sing-box/log"
+	E "github.com/sagernet/sing/common/exceptions"
+
+	"github.com/vishvananda/netlink"
+)
+
+var _ InterfaceMonitor = (*monitor)(nil)
+
+type monitor struct {
+	logger                log.Logger
+	defaultInterfaceName  string
+	defaultInterfaceIndex int
+	update                chan netlink.RouteUpdate
+	close                 chan struct{}
+}
+
+func New(logger log.Logger) (InterfaceMonitor, error) {
+	return &monitor{
+		logger: logger,
+		update: make(chan netlink.RouteUpdate, 2),
+		close:  make(chan struct{}),
+	}, nil
+}
+
+func (m *monitor) Start() error {
+	err := netlink.RouteSubscribe(m.update, m.close)
+	if err != nil {
+		return err
+	}
+	err = m.checkUpdate()
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+func (m *monitor) loopUpdate() {
+	for {
+		select {
+		case <-m.close:
+			return
+		case <-m.update:
+			err := m.checkUpdate()
+			if err != nil {
+				m.logger.Error(E.Cause(err, "check default interface"))
+			}
+		}
+	}
+}
+
+func (m *monitor) checkUpdate() error {
+	routes, err := netlink.RouteList(nil, netlink.FAMILY_V4)
+	if err != nil {
+		return err
+	}
+	for _, route := range routes {
+		if route.Dst != nil {
+			continue
+		}
+		var link netlink.Link
+		link, err = netlink.LinkByIndex(route.LinkIndex)
+		if err != nil {
+			return err
+		}
+
+		if link.Type() == "tuntap" {
+			continue
+		}
+
+		m.defaultInterfaceName = link.Attrs().Name
+		m.defaultInterfaceIndex = link.Attrs().Index
+
+		m.logger.Info("updated default interface ", m.defaultInterfaceName, ", index ", m.defaultInterfaceIndex)
+		return nil
+	}
+	return E.New("no route to internet")
+}
+
+func (m *monitor) Close() error {
+	select {
+	case <-m.close:
+		return os.ErrClosed
+	default:
+	}
+	close(m.close)
+	return nil
+}
+
+func (m *monitor) DefaultInterfaceName() string {
+	return m.defaultInterfaceName
+}
+
+func (m *monitor) DefaultInterfaceIndex() int {
+	return m.defaultInterfaceIndex
+}

common/iffmonitor/monitor_other.go

@@ -0,0 +1,13 @@
+//go:build !linux
+
+package iffmonitor
+
+import (
+	"os"
+
+	"github.com/sagernet/sing-box/log"
+)
+
+func New(logger log.Logger) (InterfaceMonitor, error) {
+	return nil, os.ErrInvalid
+}

common/tun/tun_linux.go

@@ -1,6 +1,7 @@
 package tun
 
 import (
+	"net"
 	"net/netip"
 
 	"github.com/vishvananda/netlink"
@@ -15,7 +16,7 @@ func Open(name string) (uintptr, error) {
 	return uintptr(tunFd), nil
 }
 
-func Configure(name string, inet4Address netip.Prefix, inet6Address netip.Prefix, mtu uint32) error {
+func Configure(name string, inet4Address netip.Prefix, inet6Address netip.Prefix, mtu uint32, autoRoute bool) error {
 	tunLink, err := netlink.LinkByName(name)
 	if err != nil {
 		return err
@@ -47,5 +48,66 @@ func Configure(name string, inet4Address netip.Prefix, inet6Address netip.Prefix
 		return err
 	}
 
+	if autoRoute {
+		if inet4Address.IsValid() {
+			err = netlink.RouteAdd(&netlink.Route{
+				Dst: &net.IPNet{
+					IP:   net.IPv4zero,
+					Mask: net.CIDRMask(0, 32),
+				},
+				LinkIndex: tunLink.Attrs().Index,
+			})
+			if err != nil {
+				return err
+			}
+		}
+		if inet6Address.IsValid() {
+			err = netlink.RouteAdd(&netlink.Route{
+				Dst: &net.IPNet{
+					IP:   net.IPv6zero,
+					Mask: net.CIDRMask(0, 128),
+				},
+				LinkIndex: tunLink.Attrs().Index,
+			})
+			if err != nil {
+				return err
+			}
+		}
+	}
+
+	return nil
+}
+
+func UnConfigure(name string, inet4Address netip.Prefix, inet6Address netip.Prefix, autoRoute bool) error {
+	if autoRoute {
+		tunLink, err := netlink.LinkByName(name)
+		if err != nil {
+			return err
+		}
+		if inet4Address.IsValid() {
+			err = netlink.RouteDel(&netlink.Route{
+				Dst: &net.IPNet{
+					IP:   net.IPv4zero,
+					Mask: net.CIDRMask(0, 32),
+				},
+				LinkIndex: tunLink.Attrs().Index,
+			})
+			if err != nil {
+				return err
+			}
+		}
+		if inet6Address.IsValid() {
+			err = netlink.RouteDel(&netlink.Route{
+				Dst: &net.IPNet{
+					IP:   net.IPv6zero,
+					Mask: net.CIDRMask(0, 128),
+				},
+				LinkIndex: tunLink.Attrs().Index,
+			})
+			if err != nil {
+				return err
+			}
+		}
+	}
 	return nil
 }

common/tun/tun_other.go

@@ -3,9 +3,18 @@
 package tun
 
 import (
+	"net/netip"
 	"os"
 )
 
 func Open(name string) (uintptr, error) {
 	return 0, os.ErrInvalid
 }
+
+func Configure(name string, inet4Address netip.Prefix, inet6Address netip.Prefix, mtu uint32, autoRoute bool) error {
+	return os.ErrInvalid
+}
+
+func UnConfigure(name string, inet4Address netip.Prefix, inet6Address netip.Prefix, autoRoute bool) error {
+	return os.ErrInvalid
+}