support zapcore.BufferedWriteSyncer as an option.

config.go

@@ -38,6 +38,12 @@ type FileLogConfig struct {
 	// Compression function for rotated files.
 	// Currently only `gzip` and empty are supported, empty means compression disabled.
 	Compression string `toml:"compression" json:"compression"`
+	// IsBuffered is true means use buffered logger.
+	IsBuffered bool `toml:"is-buffered" json:"is-buffered"`
+	// BufferSize is the size of the buffer.
+	BufferSize int `toml:"buffer-size" json:"buffer-size"`
+	// BufferFlushInterval is the interval of buffer flush.
+	BufferFlushInterval time.Duration `toml:"buffer-flush-interval" json:"buffer-flush-interval"`
 }
 
 // Config serializes log related config in toml/json.

log.go

@@ -49,7 +49,15 @@ func InitLogger(cfg *Config, opts ...zap.Option) (*zap.Logger, *ZapProperties, e
 		if err != nil {
 			return nil, nil, err
 		}
-		output = zapcore.AddSync(lg)
+		if cfg.File.IsBuffered {
+			output = &zapcore.BufferedWriteSyncer{
+				WS:            zapcore.AddSync(lg),
+				Size:          cfg.File.BufferSize,
+				FlushInterval: cfg.File.BufferFlushInterval,
+			}
+		} else {
+			output = zapcore.AddSync(lg)
+		}
 	} else {
 		stdOut, _, err := zap.Open([]string{"stdout"}...)
 		if err != nil {
@@ -258,6 +266,8 @@ func S() *zap.SugaredLogger {
 
 // ReplaceGlobals replaces the global Logger and SugaredLogger, and returns a
 // function to restore the original values. It's safe for concurrent use.
+// Be careful when using this with buffered logger, the flush goroutine in
+// https://pkg.go.dev/go.uber.org/zap/zapcore#BufferedWriteSyncer will not be stopped.
 func ReplaceGlobals(logger *zap.Logger, props *ZapProperties) func() {
 	// TODO: This globalMu can be replaced by atomic.Swap(), available since go1.17.
 	globalMu.Lock()

zap_log_test.go

@@ -197,6 +197,91 @@ func TestRotateLog(t *testing.T) {
 	_ = os.RemoveAll(tempDir)
 }
 
+func TestBufferedLog(t *testing.T) {
+	tempDir, _ := os.MkdirTemp("/tmp", "buffered-tests-log")
+	conf := &Config{
+		Level: "info",
+		File: FileLogConfig{
+			Filename:            tempDir + "/test.log",
+			MaxSize:             10, // no rotate
+			IsBuffered:          true,
+			BufferSize:          1024,
+			BufferFlushInterval: 3 * time.Second,
+		},
+	}
+
+	bufferedLogger, _, err := InitLogger(conf)
+	require.NoError(t, err)
+
+	logFile := filepath.Join(tempDir, "test.log")
+
+	bufferedLogger.Info("first message")
+	content, err := os.ReadFile(logFile)
+	if err == nil {
+		require.Empty(t, content, "expected empty before time-based flush")
+	} else {
+		require.True(t, os.IsNotExist(err), "expected file not exist before time-based flush")
+	}
+
+	require.Eventually(t, func() bool {
+		data, err := os.ReadFile(logFile)
+		return err == nil && strings.Contains(string(data), "first message")
+	}, 5*time.Second, 100*time.Millisecond, "expected data flushed after interval")
+
+	longMsg := strings.Repeat("x", 200)
+	for i := 0; i < 20; i++ { // Larger than buffer size
+		bufferedLogger.Info("big message", zap.String("msg", longMsg))
+	}
+
+	require.Eventually(t, func() bool {
+		data, err := os.ReadFile(logFile)
+		return err == nil && strings.Contains(string(data), "big message")
+	}, 1*time.Second, 100*time.Millisecond, "expected data flushed after buffer size exceeded")
+
+	_ = os.RemoveAll(tempDir)
+}
+
+func TestBufferedLogWithRotate(t *testing.T) {
+	tempDir, _ := os.MkdirTemp("/tmp", "buffered-rotate-tests-log")
+	conf := &Config{
+		Level: "info",
+		File: FileLogConfig{
+			Filename:            filepath.Join(tempDir, "test.log"),
+			MaxSize:             1, // 1 MB
+			IsBuffered:          true,
+			BufferSize:          4 * 1024,
+			BufferFlushInterval: 5 * time.Second,
+		},
+	}
+
+	bufferedLogger, _, err := InitLogger(conf)
+	require.NoError(t, err)
+
+	largeMsg := strings.Repeat("x", 200*1024)
+
+	for i := 0; i < 10; i++ {
+		bufferedLogger.Info("rotating message", zap.String("msg", largeMsg))
+	}
+
+	require.Eventually(t, func() bool {
+		files, err := os.ReadDir(tempDir)
+		if err != nil {
+			return false
+		}
+		return len(files) >= 2
+	}, 5*time.Second, 200*time.Millisecond, "expected log rotation after buffer flush")
+
+	files, _ := os.ReadDir(tempDir)
+	var totalSize int64
+	for _, f := range files {
+		info, _ := f.Info()
+		totalSize += info.Size()
+	}
+	require.Greater(t, totalSize, int64(1*1024*1024), "expected total written logs > 1MB")
+
+	_ = os.RemoveAll(tempDir)
+}
+
 func TestErrorLog(t *testing.T) {
 	ts := newTestLogSpy(t)
 	conf := &Config{Level: "debug", DisableTimestamp: true}
@@ -232,8 +317,8 @@ func TestLogJSON(t *testing.T) {
 		"backoff", time.Second,
 	)
 	logger.With(zap.String("connID", "1"), zap.String("traceID", "dse1121")).Info("new connection")
-	ts.assertMessages("{\"level\":\"INFO\",\"caller\":\"zap_log_test.go:229\",\"message\":\"failed to fetch URL\",\"url\":\"http://example.com\",\"attempt\":3,\"backoff\":\"1s\"}",
-		"{\"level\":\"INFO\",\"caller\":\"zap_log_test.go:234\",\"message\":\"new connection\",\"connID\":\"1\",\"traceID\":\"dse1121\"}")
+	ts.assertMessages("{\"level\":\"INFO\",\"caller\":\"zap_log_test.go:314\",\"message\":\"failed to fetch URL\",\"url\":\"http://example.com\",\"attempt\":3,\"backoff\":\"1s\"}",
+		"{\"level\":\"INFO\",\"caller\":\"zap_log_test.go:319\",\"message\":\"new connection\",\"connID\":\"1\",\"traceID\":\"dse1121\"}")
 }
 
 func TestRotateLogWithCompress(t *testing.T) {
@@ -279,8 +364,8 @@ func TestCompressError(t *testing.T) {
 	conf := &Config{
 		Level: "info",
 		File: FileLogConfig{
-			Filename: tempDir + "/test.log",
-			MaxSize:  1,
+			Filename:    tempDir + "/test.log",
+			MaxSize:     1,
 			Compression: "xxx",
 		},
 	}