net/netmon: remove usage of direct callbacks from netmon (#17292)

The callback itself is not removed as it is used in other repos, making
it simpler for those to slowly transition to the eventbus.

Updates #15160

Signed-off-by: Claus Lensbøl <claus@tailscale.com>

cmd/tailscaled/debug.go

@@ -104,14 +104,10 @@ func runMonitor(ctx context.Context, loop bool) error {
 	}
 	defer mon.Close()
 
-	mon.RegisterChangeCallback(func(delta *netmon.ChangeDelta) {
-		if !delta.Major {
-			log.Printf("Network monitor fired; not a major change")
-			return
-		}
-		log.Printf("Network monitor fired. New state:")
-		dump(delta.New)
-	})
+	eventClient := b.Client("debug.runMonitor")
+	m := eventClient.Monitor(changeDeltaWatcher(eventClient, ctx, dump))
+	defer m.Close()
+
 	if loop {
 		log.Printf("Starting link change monitor; initial state:")
 	}
@@ -124,6 +120,27 @@ func runMonitor(ctx context.Context, loop bool) error {
 	select {}
 }
 
+func changeDeltaWatcher(ec *eventbus.Client, ctx context.Context, dump func(st *netmon.State)) func(*eventbus.Client) {
+	changeSub := eventbus.Subscribe[netmon.ChangeDelta](ec)
+	return func(ec *eventbus.Client) {
+		for {
+			select {
+			case <-ctx.Done():
+				return
+			case <-ec.Done():
+				return
+			case delta := <-changeSub.Events():
+				if !delta.Major {
+					log.Printf("Network monitor fired; not a major change")
+					return
+				}
+				log.Printf("Network monitor fired. New state:")
+				dump(delta.New)
+			}
+		}
+	}
+}
+
 func getURL(ctx context.Context, urlStr string) error {
 	if urlStr == "login" {
 		urlStr = "https://login.tailscale.com"

cmd/tailscaled/tailscaled.go

@@ -433,7 +433,13 @@ func run() (err error) {
 
 	var publicLogID logid.PublicID
 	if buildfeatures.HasLogTail {
-		pol := logpolicy.New(logtail.CollectionNode, netMon, sys.HealthTracker.Get(), nil /* use log.Printf */)
+
+		pol := logpolicy.Options{
+			Collection: logtail.CollectionNode,
+			NetMon:     netMon,
+			Health:     sys.HealthTracker.Get(),
+			Bus:        sys.Bus.Get(),
+		}.New()
 		pol.SetVerbosityLevel(args.verbose)
 		publicLogID = pol.PublicID
 		logPol = pol
@@ -470,7 +476,7 @@ func run() (err error) {
 	// Always clean up, even if we're going to run the server. This covers cases
 	// such as when a system was rebooted without shutting down, or tailscaled
 	// crashed, and would for example restore system DNS configuration.
-	dns.CleanUp(logf, netMon, sys.HealthTracker.Get(), args.tunname)
+	dns.CleanUp(logf, netMon, sys.Bus.Get(), sys.HealthTracker.Get(), args.tunname)
 	router.CleanUp(logf, netMon, args.tunname)
 	// If the cleanUp flag was passed, then exit.
 	if args.cleanUp {
@@ -616,6 +622,7 @@ func getLocalBackend(ctx context.Context, logf logger.Logf, logID logid.PublicID
 	}
 
 	dialer := &tsdial.Dialer{Logf: logf} // mutated below (before used)
+	dialer.SetBus(sys.Bus.Get())
 	sys.Set(dialer)
 
 	onlyNetstack, err := createEngine(logf, sys)

cmd/tsconnect/wasm/wasm_js.go

@@ -104,6 +104,7 @@ func newIPN(jsConfig js.Value) map[string]any {
 	sys := tsd.NewSystem()
 	sys.Set(store)
 	dialer := &tsdial.Dialer{Logf: logf}
+	dialer.SetBus(sys.Bus.Get())
 	eng, err := wgengine.NewUserspaceEngine(logf, wgengine.Config{
 		Dialer:        dialer,
 		SetSubsystem:  sys.Set,
@@ -463,7 +464,6 @@ func (s *jsSSHSession) Run() {
 		cols = s.pendingResizeCols
 	}
 	err = session.RequestPty("xterm", rows, cols, ssh.TerminalModes{})
-
 	if err != nil {
 		writeError("Pseudo Terminal", err)
 		return