chore(portforward): improve loop reliability

- handle settings update within run function
- signal back start result to update call
- update loop settings only when service is started

internal/portforward/loop.go

@@ -27,8 +27,9 @@ type Loop struct {
 	// when performing an update
 	runCtx        context.Context //nolint:containedctx
 	runCancel     context.CancelFunc
-	updatedSignal chan<- struct{}
 	runDone       <-chan struct{}
+	updateTrigger chan<- service.Settings
+	updatedResult <-chan error
 }
 
 func NewLoop(settings settings.PortForwarding, routing Routing,
@@ -52,26 +53,39 @@ func (l *Loop) Start(_ context.Context) (runError <-chan error, _ error) {
 	runDone := make(chan struct{})
 	l.runDone = runDone
 
-	updatedSignal := make(chan struct{})
-	l.updatedSignal = updatedSignal
+	updateTrigger := make(chan service.Settings)
+	l.updateTrigger = updateTrigger
+	updateResult := make(chan error)
+	l.updatedResult = updateResult
 	runErrorCh := make(chan error)
 
-	go l.run(l.runCtx, runDone, runErrorCh, updatedSignal)
+	go l.run(l.runCtx, runDone, runErrorCh,
+		l.settings, updateTrigger, updateResult)
 
 	return runErrorCh, nil
 }
 
 func (l *Loop) run(runCtx context.Context, runDone chan<- struct{},
-	runErrorCh chan<- error, updatedSignal <-chan struct{}) {
+	runErrorCh chan<- error, initialSettings service.Settings,
+	updateTrigger <-chan service.Settings, updateResult chan<- error) {
 	defer close(runDone)
 
+	settings := initialSettings
 	var serviceRunError <-chan error
 	for {
+		updateReceived := false
 		select {
 		case <-runCtx.Done():
 			// Stop call takes care of stopping the service
 			return
-		case <-updatedSignal: // first and subsequent start trigger
+		case partialUpdate := <-updateTrigger:
+			updatedSettings, err := settings.UpdateWith(partialUpdate)
+			if err != nil {
+				updateResult <- err
+				continue
+			}
+			settings = updatedSettings
+			updateReceived = true
 		case err := <-serviceRunError:
 			l.logger.Error(err.Error())
 		}
@@ -85,37 +99,40 @@ func (l *Loop) run(runCtx context.Context, runDone chan<- struct{},
 			}
 		}
 
-		l.settingsMutex.RLock()
-		l.service = service.New(l.settings, l.routing, l.client,
+		l.service = service.New(settings, l.routing, l.client,
 			l.portAllower, l.logger, l.uid, l.gid)
-		l.settingsMutex.RUnlock()
 
 		var err error
 		serviceRunError, err = l.service.Start(runCtx)
+		if updateReceived {
+			// Signal to the Update call that the service has started
+			// and if it failed to start.
+			updateResult <- err
+		}
 		if err != nil {
 			if runCtx.Err() == nil { // crashed but NOT stopped
 				runErrorCh <- fmt.Errorf("starting new service: %w", err)
 			}
 			return
 		}
+
+		// Service is created and started successfully, so update
+		// the settings for external calls such as GetSettings.
+		l.settingsMutex.Lock()
+		l.settings = settings
+		l.settingsMutex.Unlock()
 	}
 }
 
 func (l *Loop) UpdateWith(partialUpdate service.Settings) (err error) {
-	l.settingsMutex.Lock()
-	l.settings, err = l.settings.UpdateWith(partialUpdate)
-	l.settingsMutex.Unlock()
-	if err != nil {
-		return err
-	}
-
 	select {
-	case l.updatedSignal <- struct{}{}:
-		// Settings are validated and if the service fails to start
-		// or crashes at runtime, the loop will stop and signal its
-		// parent goroutine. Settings validation should be the only
-		// error feedback for the caller of `Update`.
-		return nil
+	case l.updateTrigger <- partialUpdate:
+		select {
+		case err = <-l.updatedResult:
+			return err
+		case <-l.runCtx.Done():
+			return l.runCtx.Err()
+		}
 	case <-l.runCtx.Done():
 		// loop has been stopped, no update can be done
 		return l.runCtx.Err()