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本文主要研究一下zerolog的LevelWriter

LevelWriter

github.com/rs/zerolog@v1.20.0/writer.go

// LevelWriter defines as interface a writer may implement in order
// to receive level information with payload.
type LevelWriter interface {
	io.Writer
	WriteLevel(level Level, p []byte) (n int, err error)
}

type Writer interface {
	Write(p []byte) (n int, err error)
}复制代码

LevelWriter接口内嵌了io.Writer接口，定义了WriteLevel方法

levelWriterAdapter

github.com/rs/zerolog@v1.20.0/writer.go

type levelWriterAdapter struct {
	io.Writer
}

func (lw levelWriterAdapter) WriteLevel(l Level, p []byte) (n int, err error) {
	return lw.Write(p)
}复制代码

levelWriterAdapter内嵌了io.Writer属性，实现了LevelWriter的WriteLevel方法，该方法内部通过io.Writer属性的Write方法来输出

syncWriter

github.com/rs/zerolog@v1.20.0/writer.go

type syncWriter struct {
	mu sync.Mutex
	lw LevelWriter
}

func SyncWriter(w io.Writer) io.Writer {
	if lw, ok := w.(LevelWriter); ok {
		return &syncWriter{lw: lw}
	}
	return &syncWriter{lw: levelWriterAdapter{w}}
}

// Write implements the io.Writer interface.
func (s *syncWriter) Write(p []byte) (n int, err error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	return s.lw.Write(p)
}

// WriteLevel implements the LevelWriter interface.
func (s *syncWriter) WriteLevel(l Level, p []byte) (n int, err error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	return s.lw.WriteLevel(l, p)
}复制代码

syncWriter实现了LevelWriter接口，其对Write及WriteLevel方法都进行了加锁；SyncWriter方法通过levelWriterAdapter来适配io.Writer

multiLevelWriter

github.com/rs/zerolog@v1.20.0/writer.go

type multiLevelWriter struct {
	writers []LevelWriter
}

func (t multiLevelWriter) Write(p []byte) (n int, err error) {
	for _, w := range t.writers {
		n, err = w.Write(p)
		if err != nil {
			return
		}
		if n != len(p) {
			err = io.ErrShortWrite
			return
		}
	}
	return len(p), nil
}

func (t multiLevelWriter) WriteLevel(l Level, p []byte) (n int, err error) {
	for _, w := range t.writers {
		n, err = w.WriteLevel(l, p)
		if err != nil {
			return
		}
		if n != len(p) {
			err = io.ErrShortWrite
			return
		}
	}
	return len(p), nil
}

// MultiLevelWriter creates a writer that duplicates its writes to all the
// provided writers, similar to the Unix tee(1) command. If some writers
// implement LevelWriter, their WriteLevel method will be used instead of Write.
func MultiLevelWriter(writers ...io.Writer) LevelWriter {
	lwriters := make([]LevelWriter, 0, len(writers))
	for _, w := range writers {
		if lw, ok := w.(LevelWriter); ok {
			lwriters = append(lwriters, lw)
		} else {
			lwriters = append(lwriters, levelWriterAdapter{w})
		}
	}
	return multiLevelWriter{lwriters}
}复制代码

multiLevelWriter定义了writers属性，它也实现了LevelWriter接口，其Write及WriteLevel方法均是遍历writers挨个执行对应操作；MultiLevelWriter方法通过levelWriterAdapter来适配io.Writer

实例

func multiLevelWriterDemo() {
	consoleWriter := zerolog.ConsoleWriter{Out: os.Stdout}
	multi := zerolog.MultiLevelWriter(consoleWriter, os.Stdout)
	logger := zerolog.New(multi).With().Timestamp().Logger()
	logger.Info().Msg("Hello World!")
}复制代码

这里使用zerolog.MultiLevelWriter来指定多个输出

输出

8:02PM INF Hello World!
{"level":"info","time":"2021-01-02T20:02:27+08:00","message":"Hello World!"}复制代码

小结

LevelWriter接口内嵌了io.Writer接口，定义了WriteLevel方法；levelWriterAdapter内嵌了io.Writer属性，实现了LevelWriter的WriteLevel方法，该方法内部通过io.Writer属性的Write方法来输出；SyncWriter方法通过levelWriterAdapter来适配io.Writer；MultiLevelWriter方法通过levelWriterAdapter来适配io.Writer。

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