Add auto_route and auto_detect_interface for linux

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
+}