聊聊golang的zap的global.go

序

本文主要研究一下golang的zap的global.go

global.go

zap@v1.16.0/global.go

var (
	_globalMu sync.RWMutex
	_globalL  = NewNop()
	_globalS  = _globalL.Sugar()
)

// L returns the global Logger, which can be reconfigured with ReplaceGlobals.
// It's safe for concurrent use.
func L() *Logger {
	_globalMu.RLock()
	l := _globalL
	_globalMu.RUnlock()
	return l
}

// S returns the global SugaredLogger, which can be reconfigured with
// ReplaceGlobals. It's safe for concurrent use.
func S() *SugaredLogger {
	_globalMu.RLock()
	s := _globalS
	_globalMu.RUnlock()
	return s
}

// ReplaceGlobals replaces the global Logger and SugaredLogger, and returns a
// function to restore the original values. It's safe for concurrent use.
func ReplaceGlobals(logger *Logger) func() {
	_globalMu.Lock()
	prev := _globalL
	_globalL = logger
	_globalS = logger.Sugar()
	_globalMu.Unlock()
	return func() { ReplaceGlobals(prev) }
}

global定义了_globalL及_globalS，L()方法通过加读锁的方式返回_globalL，S()通过加读锁的方式返回_globalS，之所以要加读锁是因为ReplaceGlobals方法会修改_globalL及_globalS

StdLog

zap@v1.16.0/global.go

// NewStdLog returns a *log.Logger which writes to the supplied zap Logger at
// InfoLevel. To redirect the standard library's package-global logging
// functions, use RedirectStdLog instead.
func NewStdLog(l *Logger) *log.Logger {
	logger := l.WithOptions(AddCallerSkip(_stdLogDefaultDepth + _loggerWriterDepth))
	f := logger.Info
	return log.New(&loggerWriter{f}, "" /* prefix */, 0 /* flags */)
}

// NewStdLogAt returns *log.Logger which writes to supplied zap logger at
// required level.
func NewStdLogAt(l *Logger, level zapcore.Level) (*log.Logger, error) {
	logger := l.WithOptions(AddCallerSkip(_stdLogDefaultDepth + _loggerWriterDepth))
	logFunc, err := levelToFunc(logger, level)
	if err != nil {
		return nil, err
	}
	return log.New(&loggerWriter{logFunc}, "" /* prefix */, 0 /* flags */), nil
}

func levelToFunc(logger *Logger, lvl zapcore.Level) (func(string, ...Field), error) {
	switch lvl {
	case DebugLevel:
		return logger.Debug, nil
	case InfoLevel:
		return logger.Info, nil
	case WarnLevel:
		return logger.Warn, nil
	case ErrorLevel:
		return logger.Error, nil
	case DPanicLevel:
		return logger.DPanic, nil
	case PanicLevel:
		return logger.Panic, nil
	case FatalLevel:
		return logger.Fatal, nil
	}
	return nil, fmt.Errorf("unrecognized level: %q", lvl)
}

type loggerWriter struct {
	logFunc func(msg string, fields ...Field)
}

func (l *loggerWriter) Write(p []byte) (int, error) {
	p = bytes.TrimSpace(p)
	l.logFunc(string(p))
	return len(p), nil
}

NewStdLog返回使用info级别的log.Logger；NewStdLogAt方法返回使用指定级别的log.Logger；levelToFunc用于返回指定level对应的zap.Logger的func；这里使用loggerWriter来包装zap.Logger到标准库的log.Logger

RedirectStdLog

// RedirectStdLog redirects output from the standard library's package-global
// logger to the supplied logger at InfoLevel. Since zap already handles caller
// annotations, timestamps, etc., it automatically disables the standard
// library's annotations and prefixing.
//
// It returns a function to restore the original prefix and flags and reset the
// standard library's output to os.Stderr.
func RedirectStdLog(l *Logger) func() {
	f, err := redirectStdLogAt(l, InfoLevel)
	if err != nil {
		// Can't get here, since passing InfoLevel to redirectStdLogAt always
		// works.
		panic(fmt.Sprintf(_programmerErrorTemplate, err))
	}
	return f
}

// RedirectStdLogAt redirects output from the standard library's package-global
// logger to the supplied logger at the specified level. Since zap already
// handles caller annotations, timestamps, etc., it automatically disables the
// standard library's annotations and prefixing.
//
// It returns a function to restore the original prefix and flags and reset the
// standard library's output to os.Stderr.
func RedirectStdLogAt(l *Logger, level zapcore.Level) (func(), error) {
	return redirectStdLogAt(l, level)
}

func redirectStdLogAt(l *Logger, level zapcore.Level) (func(), error) {
	flags := log.Flags()
	prefix := log.Prefix()
	log.SetFlags(0)
	log.SetPrefix("")
	logger := l.WithOptions(AddCallerSkip(_stdLogDefaultDepth + _loggerWriterDepth))
	logFunc, err := levelToFunc(logger, level)
	if err != nil {
		return nil, err
	}
	log.SetOutput(&loggerWriter{logFunc})
	return func() {
		log.SetFlags(flags)
		log.SetPrefix(prefix)
		log.SetOutput(os.Stderr)
	}, nil
}

RedirectStdLog把标准库的log.Logger的info级别的输出重定向到zap.Logger；RedirectStdLogAt把标准库的log.Logger的指定级别的输出重定向到zap.Logger

实例

func globalDemo() {
	logger, _ := zap.NewProduction()
	defer logger.Sync() // flushes buffer, if any
	zap.ReplaceGlobals(logger)
	zap.S().Info("hello")

	stdLog := zap.NewStdLog(logger)
	stdLog.Println("this is standard logger but log with output to zap logger")

	undo := zap.RedirectStdLog(logger)
	log.Println("standard log will redirect to zap.Logger")
	undo()
	log.Println("standard log with original output")
}

输出

{"level":"info","ts":1607860586.171433,"caller":"zap/zap_demo.go:23","msg":"hello"}
{"level":"info","ts":1607860586.171505,"caller":"zap/zap_demo.go:26","msg":"this is standard logger but log with output to zap logger"}
{"level":"info","ts":1607860586.1715178,"caller":"zap/zap_demo.go:29","msg":"standard log will redirect to zap.Logger"}
2020/12/13 19:56:26 standard log with original output

小结

global.go提供了ReplaceGlobals方法用于注册全局的单例的logger；提供了NewStdLog方法用于返回标准库的log.Logger，然后使用该logger的输出都会通过zap.Logger来输出；提供了RedirectStdLog方法用于改变全局的标准库的log的输出，将其通过zap.Logger来输出，该方法返回一个func来撤销这种重定向。

doc

• zap