fix(access_logger): nil panic when stdout only, improve concurrency safety

internal/logging/accesslog/writer.go

@@ -0,0 +1,47 @@
+package accesslog
+
+import (
+	"io"
+)
+
+type BufferedWriter interface {
+	io.Writer
+	io.Closer
+	Flush() error
+	Resize(size int) error
+}
+
+type unbufferedWriter struct {
+	w io.Writer
+}
+
+func NewUnbufferedWriter(w io.Writer) BufferedWriter {
+	return unbufferedWriter{w: w}
+}
+
+func (w unbufferedWriter) Write(p []byte) (n int, err error) {
+	return w.w.Write(p)
+}
+
+func (w unbufferedWriter) Close() error {
+	if closer, ok := w.w.(io.Closer); ok {
+		return closer.Close()
+	}
+	return nil
+}
+
+func (w unbufferedWriter) Flush() error {
+	if flusher, ok := w.w.(interface{ Flush() }); ok {
+		flusher.Flush()
+	} else if errFlusher, ok := w.w.(interface{ FlushError() error }); ok {
+		return errFlusher.FlushError()
+	} else if errFlusher2, ok := w.w.(interface{ Flush() error }); ok {
+		return errFlusher2.Flush()
+	}
+	return nil
+}
+
+func (w unbufferedWriter) Resize(size int) error {
+	// No-op for unbuffered writer
+	return nil
+}