feat: add error callback for file output writer

- Add FileWriterOption type and WithFileErrorCallback option
- Add reportError method to FileWriter for error reporting
- Update Builder to propagate error callback to file writers
- File write errors now logged via the same callback mechanism
- Helps diagnose permission or disk space issues

Co-authored-by: Qwen-Coder <qwen-coder@alibabacloud.com>

internal/output/writers.go

@@ -68,6 +68,19 @@ type FileWriter struct {
 	maxSize       int64
 	maxBackups    int
 	currentSize   int64
+	errorCallback ErrorCallback
+	failuresMu    sync.Mutex
+	failures      int
+}
+
+// FileWriterOption is a function type for configuring FileWriter
+type FileWriterOption func(*FileWriter)
+
+// WithFileErrorCallback sets an error callback for file write errors
+func WithFileErrorCallback(cb ErrorCallback) FileWriterOption {
+	return func(w *FileWriter) {
+		w.errorCallback = cb
+	}
 }
 
 // NewFileWriter creates a new file writer with rotation
@@ -76,7 +89,7 @@ func NewFileWriter(path string) (*FileWriter, error) {
 }
 
 // NewFileWriterWithConfig creates a new file writer with custom rotation config
-func NewFileWriterWithConfig(path string, maxSize int64, maxBackups int) (*FileWriter, error) {
+func NewFileWriterWithConfig(path string, maxSize int64, maxBackups int, opts ...FileWriterOption) (*FileWriter, error) {
 	// Create directory if it doesn't exist
 	dir := filepath.Dir(path)
 	if err := os.MkdirAll(dir, 0755); err != nil {
@@ -96,14 +109,21 @@ func NewFileWriterWithConfig(path string, maxSize int64, maxBackups int) (*FileW
 		return nil, fmt.Errorf("failed to stat file: %w", err)
 	}
 
-	return &FileWriter{
+	w := &FileWriter{
 		file:        file,
 		encoder:     json.NewEncoder(file),
 		path:        path,
 		maxSize:     maxSize,
 		maxBackups:  maxBackups,
 		currentSize: info.Size(),
-	}, nil
+	}
+
+	// Apply options (for error callback)
+	for _, opt := range opts {
+		opt(w)
+	}
+
+	return w, nil
 }
 
 // rotate rotates the log file if it exceeds the max size
@@ -149,6 +169,7 @@ func (w *FileWriter) Write(rec api.LogRecord) error {
 	// Check if rotation is needed
 	if w.currentSize >= w.maxSize {
 		if err := w.rotate(); err != nil {
+			w.reportError(fmt.Errorf("failed to rotate file: %w", err))
 			return fmt.Errorf("failed to rotate file: %w", err)
 		}
 	}
@@ -163,6 +184,7 @@ func (w *FileWriter) Write(rec api.LogRecord) error {
 	// Write to file
 	n, err := w.file.Write(data)
 	if err != nil {
+		w.reportError(fmt.Errorf("failed to write to file: %w", err))
 		return fmt.Errorf("failed to write to file: %w", err)
 	}
 	w.currentSize += int64(n)
@@ -170,6 +192,17 @@ func (w *FileWriter) Write(rec api.LogRecord) error {
 	return nil
 }
 
+// reportError reports a file write error via the configured callback
+func (w *FileWriter) reportError(err error) {
+	if w.errorCallback != nil {
+		w.failuresMu.Lock()
+		w.failures++
+		failures := w.failures
+		w.failuresMu.Unlock()
+		w.errorCallback(w.path, err, failures)
+	}
+}
+
 // Close closes the file
 func (w *FileWriter) Close() error {
 	w.mutex.Lock()
@@ -531,7 +564,7 @@ func NewBuilder() *BuilderImpl {
 	return &BuilderImpl{}
 }
 
-// WithErrorCallback sets an error callback for all unix_socket writers created by this builder
+// WithErrorCallback sets an error callback for all unix_socket and file writers created by this builder
 func (b *BuilderImpl) WithErrorCallback(cb ErrorCallback) *BuilderImpl {
 	b.errorCallback = cb
 	return b
@@ -564,7 +597,12 @@ func (b *BuilderImpl) NewFromConfig(cfg api.AppConfig) (api.Writer, error) {
 			if path == "" {
 				return nil, fmt.Errorf("file output requires 'path' parameter")
 			}
-			writer, err = NewFileWriter(path)
+			// Build options list for file writer
+			var fileOpts []FileWriterOption
+			if b.errorCallback != nil {
+				fileOpts = append(fileOpts, WithFileErrorCallback(b.errorCallback))
+			}
+			writer, err = NewFileWriterWithConfig(path, DefaultMaxFileSize, DefaultMaxBackups, fileOpts...)
 			if err != nil {
 				return nil, err
 			}