Monitor network changes and restart engine on detection (#1904)

client/internal/networkmonitor/monitor_linux.go

@@ -0,0 +1,81 @@
+//go:build !android
+
+package networkmonitor
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"net"
+	"net/netip"
+	"syscall"
+
+	log "github.com/sirupsen/logrus"
+	"github.com/vishvananda/netlink"
+)
+
+func checkChange(ctx context.Context, nexthopv4 netip.Addr, intfv4 *net.Interface, nexthop6 netip.Addr, intfv6 *net.Interface, callback func()) error {
+	if intfv4 == nil && intfv6 == nil {
+		return errors.New("no interfaces available")
+	}
+
+	linkChan := make(chan netlink.LinkUpdate)
+	done := make(chan struct{})
+	defer close(done)
+
+	if err := netlink.LinkSubscribe(linkChan, done); err != nil {
+		return fmt.Errorf("subscribe to link updates: %v", err)
+	}
+
+	routeChan := make(chan netlink.RouteUpdate)
+	if err := netlink.RouteSubscribe(routeChan, done); err != nil {
+		return fmt.Errorf("subscribe to route updates: %v", err)
+	}
+
+	log.Info("Network monitor: started")
+	for {
+		select {
+		case <-ctx.Done():
+			return ctx.Err()
+
+		// handle interface state changes
+		case update := <-linkChan:
+			if (intfv4 == nil || update.Index != int32(intfv4.Index)) && (intfv6 == nil || update.Index != int32(intfv6.Index)) {
+				continue
+			}
+
+			switch update.Header.Type {
+			case syscall.RTM_DELLINK:
+				log.Infof("Network monitor: monitored interface (%s) is gone", update.Link.Attrs().Name)
+				callback()
+				return nil
+			case syscall.RTM_NEWLINK:
+				if (update.IfInfomsg.Flags&syscall.IFF_RUNNING) == 0 && update.Link.Attrs().OperState == netlink.OperDown {
+					log.Infof("Network monitor: monitored interface (%s) is down.", update.Link.Attrs().Name)
+					callback()
+					return nil
+				}
+			}
+
+		// handle route changes
+		case route := <-routeChan:
+			// default route and main table
+			if route.Dst != nil || route.Table != syscall.RT_TABLE_MAIN {
+				continue
+			}
+			switch route.Type {
+			// triggered on added/replaced routes
+			case syscall.RTM_NEWROUTE:
+				log.Infof("Network monitor: default route changed: via %s, interface %d", route.Gw, route.LinkIndex)
+				callback()
+				return nil
+			case syscall.RTM_DELROUTE:
+				if intfv4 != nil && route.Gw.Equal(nexthopv4.AsSlice()) || intfv6 != nil && route.Gw.Equal(nexthop6.AsSlice()) {
+					log.Infof("Network monitor: default route removed: via %s, interface %d", route.Gw, route.LinkIndex)
+					callback()
+					return nil
+				}
+			}
+		}
+	}
+}