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

client/internal/networkmonitor/monitor_generic.go

@@ -0,0 +1,82 @@
+//go:build !ios && !android
+
+package networkmonitor
+
+import (
+	"context"
+	"errors"
+	"net"
+	"net/netip"
+	"runtime/debug"
+
+	"github.com/cenkalti/backoff/v4"
+	log "github.com/sirupsen/logrus"
+
+	"github.com/netbirdio/netbird/client/internal/routemanager"
+)
+
+// Start begins watching for network changes and calls the callback function and stops when a change is detected.
+func (nw *NetworkWatcher) Start(ctx context.Context, callback func()) {
+	if nw.cancel != nil {
+		log.Warn("Network monitor: already running, stopping previous watcher")
+		nw.Stop()
+	}
+
+	if ctx.Err() != nil {
+		log.Info("Network monitor: not starting, context is already cancelled")
+		return
+	}
+
+	ctx, nw.cancel = context.WithCancel(ctx)
+	defer nw.Stop()
+
+	var nexthop4, nexthop6 netip.Addr
+	var intf4, intf6 *net.Interface
+
+	operation := func() error {
+		var errv4, errv6 error
+		nexthop4, intf4, errv4 = routemanager.GetNextHop(netip.IPv4Unspecified())
+		nexthop6, intf6, errv6 = routemanager.GetNextHop(netip.IPv6Unspecified())
+
+		if errv4 != nil && errv6 != nil {
+			return errors.New("failed to get default next hops")
+		}
+
+		if errv4 == nil {
+			log.Debugf("Network monitor: IPv4 default route: %s, interface: %s", nexthop4, intf4.Name)
+		}
+		if errv6 == nil {
+			log.Debugf("Network monitor: IPv6 default route: %s, interface: %s", nexthop6, intf6.Name)
+		}
+
+		// continue if either route was found
+		return nil
+	}
+
+	expBackOff := backoff.WithContext(backoff.NewExponentialBackOff(), ctx)
+
+	if err := backoff.Retry(operation, expBackOff); err != nil {
+		log.Errorf("Network monitor: failed to get default next hops: %v", err)
+		return
+	}
+
+	// recover in case sys ops panic
+	defer func() {
+		if r := recover(); r != nil {
+			log.Errorf("Network monitor: panic occurred: %v, stack trace: %s", r, string(debug.Stack()))
+		}
+	}()
+
+	if err := checkChange(ctx, nexthop4, intf4, nexthop6, intf6, callback); err != nil && !errors.Is(err, context.Canceled) {
+		log.Errorf("Network monitor: failed to start: %v", err)
+	}
+}
+
+// Stop stops the network monitor.
+func (nw *NetworkWatcher) Stop() {
+	if nw.cancel != nil {
+		nw.cancel()
+		nw.cancel = nil
+		log.Info("Network monitor: stopped")
+	}
+}