How to add zapcore.NewMultiWriteSyncer in zap.Config

[moluzhui]

I am working on a log package and hope to configure whether to use log rotation through switches.

Previous code did not support log rotate

// using zap.Config and cannot log rotate

// Build constructs a global zap logger from the Config and Options.
func (o *Options) Build() error {
	var zapLevel zapcore.Level
	if err := zapLevel.UnmarshalText([]byte(o.Level)); err != nil {
		zapLevel = zapcore.InfoLevel
	}
	encodeLevel := zapcore.CapitalLevelEncoder
	if o.Format == consoleFormat && o.EnableColor {
		encodeLevel = zapcore.CapitalColorLevelEncoder
	}

	zc := &zap.Config{
		Level:             zap.NewAtomicLevelAt(zapLevel),
		Development:       o.Development,
		DisableCaller:     o.DisableCaller,
		DisableStacktrace: o.DisableStacktrace,
		Sampling: &zap.SamplingConfig{
			Initial:    100,
			Thereafter: 100,
		},
		Encoding: o.Format,
		EncoderConfig: zapcore.EncoderConfig{
			MessageKey:     "message",
			LevelKey:       "level",
			TimeKey:        "timestamp",
			NameKey:        "logger",
			CallerKey:      "caller",
			StacktraceKey:  "stacktrace",
			LineEnding:     zapcore.DefaultLineEnding,
			EncodeLevel:    encodeLevel,
			EncodeTime:     timeEncoder,
			EncodeDuration: milliSecondsDurationEncoder,
			EncodeCaller:   zapcore.ShortCallerEncoder,
			EncodeName:     zapcore.FullNameEncoder,
		},
		OutputPaths:      o.OutputPaths,
		ErrorOutputPaths: o.ErrorOutputPaths,
	}
	
	logger, err := zc.Build(zap.AddStacktrace(zapcore.PanicLevel))
	if err != nil {
		return err
	}
	zap.RedirectStdLog(logger.Named(o.Name))
	zap.ReplaceGlobals(logger)

	return nil
}

Now I hope to support rotation. I checked the relevant information and found that it can be rotated in the following way

//   logrotate.log
syncer :=zapcore.NewMultiWriteSyncer(zapcore.AddSync(os.Stdout), zapcore.AddSync(lumberJackLogger))   
// lumberJackLogger encapsulate lumberjack.Logger

core := zapcore.NewCore(
		zapcore.NewJSONEncoder(zap.NewProductionEncoderConfig()),
		syncer,
		logLevel,
	)
logger := zap.New(core, zap.AddCaller(), zap.AddStacktrace(zap.ErrorLevel))

I hope to change OutputPaths and ErrorOutputPaths into the form of logrorate.go when starting rotation based on config.

Just like the following pseudo code

if ! o.EnableRorate
  zap.Config{...OutputPaths,ErrorOutputPaths}
else
   zap.config add zapcore.NewMultiWriteSyncer

Please tell me what I need to do to achieve my expectations. Looking forward to your reply

PS: I hope that other configurations besides o.OutputPaths and o.ErrorOutputPaths can still be used under the new solution.

[moluzhui]

I searched and found that it can be achieved using zap.WrapCore.

// hack replace zap config build core with lumberjack logger
func (o *Options) replaceLogCore(conf zap.Config) zap.Option {
    var enc zapcore.Encoder
    // Copy paste from zap.Config.buildEncoder.
    switch conf.Encoding {
    case jsonFormat:
        enc = zapcore.NewJSONEncoder(conf.EncoderConfig)
    case consoleFormat:
        enc = zapcore.NewConsoleEncoder(conf.EncoderConfig)
    default:
        panic("unknown encoding")
    }

    logSyncer := zapcore.AddSync(&lumberjack.Logger{
        Filename:   o.RotateLogPath,
        MaxSize:    o.RotateMaxSize, //MB
        MaxBackups: o.RotateMaxBackups,
        MaxAge:     o.RotateMaxAge, //days
        LocalTime:  o.RotateEnableLocalTime,
        Compress:   o.RotateEnableCompress,
    })

    return zap.WrapCore(func(zapcore.Core) zapcore.Core {
        return zapcore.NewCore(enc, logSyncer, conf.Level)
    })
}

Reference