fix: log duplication on log senders

When the buffer Writer is request, code unconditionally started all
senders (in our case, this was always JSON network senders).

This resulted in log duplication on service restart - each time service
is started, the senders goroutine was recreated.

Signed-off-by: Andrey Smirnov <andrey.smirnov@siderolabs.com>
(cherry picked from commit 75e4c4a)

Author: smira

internal/app/machined/pkg/runtime/logging/circular.go

@@ -115,26 +115,28 @@ func (manager *CircularBufferLoggingManager) getSenders() []runtime.LogSender {
 	}
 }
 
-func (manager *CircularBufferLoggingManager) getBuffer(id string, create bool) (*circular.Buffer, error) {
+func (manager *CircularBufferLoggingManager) getBuffer(id string, create bool) (*circular.Buffer, bool, error) {
 	buf, ok := manager.buffers.Load(id)
-	if !ok {
-		if !create {
-			return nil, nil
-		}
+	if ok {
+		return buf.(*circular.Buffer), false, nil
+	}
 
-		b, err := circular.NewBuffer(
-			circular.WithInitialCapacity(InitialCapacity),
-			circular.WithMaxCapacity(ChunkCapacity),
-			circular.WithNumCompressedChunks(NumCompressedChunks, manager.compressor),
-			circular.WithSafetyGap(SafetyGap))
-		if err != nil {
-			return nil, err // only configuration issue might raise error
-		}
+	if !create {
+		return nil, false, nil
+	}
 
-		buf, _ = manager.buffers.LoadOrStore(id, b)
+	b, err := circular.NewBuffer(
+		circular.WithInitialCapacity(InitialCapacity),
+		circular.WithMaxCapacity(ChunkCapacity),
+		circular.WithNumCompressedChunks(NumCompressedChunks, manager.compressor),
+		circular.WithSafetyGap(SafetyGap))
+	if err != nil {
+		return nil, false, err // only configuration issue might raise error
 	}
 
-	return buf.(*circular.Buffer), nil
+	buf, _ = manager.buffers.LoadOrStore(id, b)
+
+	return buf.(*circular.Buffer), true, nil
 }
 
 // RegisteredLogs implements runtime.LoggingManager interface.
@@ -169,24 +171,29 @@ func (nopCloser) Close() error {
 // Writer implements runtime.LogHandler interface.
 func (handler *circularHandler) Writer() (io.WriteCloser, error) {
 	if handler.buf == nil {
-		var err error
+		var (
+			created bool
+			err     error
+		)
 
-		handler.buf, err = handler.manager.getBuffer(handler.id, true)
+		handler.buf, created, err = handler.manager.getBuffer(handler.id, true)
 		if err != nil {
 			return nil, err
 		}
 
-		go func() {
-			defer func() {
-				if r := recover(); r != nil {
-					handler.manager.fallbackLogger.Printf("log sender panic: %v", r)
+		if created {
+			go func() {
+				defer func() {
+					if r := recover(); r != nil {
+						handler.manager.fallbackLogger.Printf("log sender panic: %v", r)
+					}
+				}()
+
+				if err := handler.runSenders(); err != nil {
+					handler.manager.fallbackLogger.Printf("log senders stopped: %s", err)
 				}
 			}()
-
-			if err := handler.runSenders(); err != nil {
-				handler.manager.fallbackLogger.Printf("log senders stopped: %s", err)
-			}
-		}()
+		}
 	}
 
 	switch handler.id {
@@ -202,7 +209,7 @@ func (handler *circularHandler) Reader(opts ...runtime.LogOption) (io.ReadCloser
 	if handler.buf == nil {
 		var err error
 
-		handler.buf, err = handler.manager.getBuffer(handler.id, false)
+		handler.buf, _, err = handler.manager.getBuffer(handler.id, false)
 		if err != nil {
 			return nil, err
 		}