关于golang:聊聊golang的zap的globalgo

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本文次要钻研一下 golang 的 zap 的 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() 办法通过加读锁的形式返回_globalL，S() 通过加读锁的形式返回_globalS，之所以要加读锁是因为 ReplaceGlobals 办法会批改_globalL 及_globalS

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 返回应用 info 级别的 log.Logger；NewStdLogAt 办法返回应用指定级别的 log.Logger；levelToFunc 用于返回指定 level 对应的 zap.Logger 的 func；这里应用 loggerWriter 来包装 zap.Logger 到规范库的 log.Logger

// 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 把规范库的 log.Logger 的 info 级别的输入重定向到 zap.Logger；RedirectStdLogAt 把规范库的 log.Logger 的指定级别的输入重定向到 zap.Logger

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")
}

输入

{"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

global.go 提供了 ReplaceGlobals 办法用于注册全局的单例的 logger；提供了 NewStdLog 办法用于返回规范库的 log.Logger，而后应用该 logger 的输入都会通过 zap.Logger 来输入；提供了 RedirectStdLog 办法用于扭转全局的规范库的 log 的输入，将其通过 zap.Logger 来输入，该办法返回一个 func 来撤销这种重定向。