TUN-3738: Refactor observer to avoid potential of blocking on tunnel notifications

cmd/cloudflared/tunnel/cmd.go

@@ -328,13 +328,9 @@ func StartServer(
 
 	transportLog := logger.CreateTransportLoggerFromContext(c, isUIEnabled)
 
-	readinessCh := make(chan connection.Event, 16)
-	uiCh := make(chan connection.Event, 16)
-	eventChannels := []chan connection.Event{
-		readinessCh,
-		uiCh,
-	}
-	tunnelConfig, ingressRules, err := prepareTunnelConfig(c, buildInfo, version, log, transportLog, namedTunnel, isUIEnabled, eventChannels)
+	observer := connection.NewObserver(log, isUIEnabled)
+
+	tunnelConfig, ingressRules, err := prepareTunnelConfig(c, buildInfo, version, log, observer, namedTunnel)
 	if err != nil {
 		log.Err(err).Msg("Couldn't start tunnel")
 		return err
@@ -349,7 +345,9 @@ func StartServer(
 	wg.Add(1)
 	go func() {
 		defer wg.Done()
-		errC <- metrics.ServeMetrics(metricsListener, shutdownC, readinessCh, log)
+		readinessServer := metrics.NewReadyServer(log)
+		observer.RegisterSink(readinessServer)
+		errC <- metrics.ServeMetrics(metricsListener, shutdownC, readinessServer, log)
 	}()
 
 	if err := ingressRules.StartOrigins(&wg, log, shutdownC, errC); err != nil {
@@ -369,20 +367,15 @@ func StartServer(
 	}()
 
 	if isUIEnabled {
-		tunnelInfo := ui.NewUIModel(
+		tunnelUI := ui.NewUIModel(
 			version,
 			hostname,
 			metricsListener.Addr().String(),
 			&ingressRules,
 			tunnelConfig.HAConnections,
 		)
-		tunnelInfo.LaunchUI(ctx, log, transportLog, uiCh)
-	} else {
-		go func() {
-			for range uiCh {
-				// Consume UI events into a noop
-			}
-		}()
+		app := tunnelUI.Launch(ctx, log, transportLog)
+		observer.RegisterSink(app)
 	}
 
 	return waitToShutdown(&wg, errC, shutdownC, graceShutdownC, c.Duration("grace-period"), log)

cmd/cloudflared/tunnel/configuration.go

@@ -157,10 +157,8 @@ func prepareTunnelConfig(
 	buildInfo *buildinfo.BuildInfo,
 	version string,
 	log *zerolog.Logger,
-	transportLogger *zerolog.Logger,
+	observer *connection.Observer,
 	namedTunnel *connection.NamedTunnelConfig,
-	isUIEnabled bool,
-	eventChans []chan connection.Event,
 ) (*origin.TunnelConfig, ingress.Ingress, error) {
 	isNamedTunnel := namedTunnel != nil
 
@@ -281,7 +279,7 @@ func prepareTunnelConfig(
 		LBPool:           c.String("lb-pool"),
 		Tags:             tags,
 		Log:              log,
-		Observer:         connection.NewObserver(transportLogger, eventChans, isUIEnabled),
+		Observer:         observer,
 		ReportedVersion:  version,
 		// Note TUN-3758 , we use Int because UInt is not supported with altsrc
 		Retries:          uint(c.Int("retries")),
@@ -289,7 +287,6 @@ func prepareTunnelConfig(
 		NamedTunnel:      namedTunnel,
 		ClassicTunnel:    classicTunnel,
 		MuxerConfig:      muxerConfig,
-		TunnelEventChans: eventChans,
 		ProtocolSelector: protocolSelector,
 		EdgeTLSConfigs:   edgeTLSConfigs,
 	}, ingressRules, nil

cmd/cloudflared/ui/launch_ui.go

@@ -48,11 +48,10 @@ func NewUIModel(version, hostname, metricsURL string, ing *ingress.Ingress, haCo
 	}
 }
 
-func (data *uiModel) LaunchUI(
+func (data *uiModel) Launch(
 	ctx context.Context,
 	log, transportLog *zerolog.Logger,
-	tunnelEventChan <-chan connection.Event,
-) {
+) connection.EventSink {
 	// Configure the logger to stream logs into the textview
 
 	// Add TextView as a group to write output to
@@ -114,28 +113,9 @@ func (data *uiModel) LaunchUI(
 	grid.AddItem(logFrame, 4, 0, 5, 2, 0, 0, false)
 
 	go func() {
-		for {
-			select {
-			case <-ctx.Done():
-				app.Stop()
-				return
-			case event := <-tunnelEventChan:
-				switch event.EventType {
-				case connection.Connected:
-					data.setConnTableCell(event, connTable, palette)
-				case connection.Disconnected, connection.Reconnecting:
-					data.changeConnStatus(event, connTable, log, palette)
-				case connection.SetURL:
-					tunnelHostText.SetText(event.URL)
-					data.edgeURL = event.URL
-				case connection.RegisteringTunnel:
-					if data.edgeURL == "" {
-						tunnelHostText.SetText("Registering tunnel...")
-					}
-				}
-			}
-			app.Draw()
-		}
+		<-ctx.Done()
+		app.Stop()
+		return
 	}()
 
 	go func() {
@@ -143,6 +123,23 @@ func (data *uiModel) LaunchUI(
 			log.Error().Msgf("Error launching UI: %s", err)
 		}
 	}()
+
+	return connection.EventSinkFunc(func(event connection.Event) {
+		switch event.EventType {
+		case connection.Connected:
+			data.setConnTableCell(event, connTable, palette)
+		case connection.Disconnected, connection.Reconnecting:
+			data.changeConnStatus(event, connTable, log, palette)
+		case connection.SetURL:
+			tunnelHostText.SetText(event.URL)
+			data.edgeURL = event.URL
+		case connection.RegisteringTunnel:
+			if data.edgeURL == "" {
+				tunnelHostText.SetText("Registering tunnel...")
+			}
+		}
+		app.Draw()
+	})
 }
 
 func NewDynamicColorTextView() *tview.TextView {