聊聊zerolog的LevelWriter

序

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)
}

LevelWriter接口內嵌了io.Writer接口，定義了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)
}

levelWriterAdapter內嵌了io.Writer屬性，實現了LevelWriter的WriteLevel方法，該方法內部經過io.Writer屬性的Write方法來輸出

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)
}

syncWriter實現了LevelWriter接口，其對Write及WriteLevel方法都進行了加鎖；SyncWriter方法經過levelWriterAdapter來適配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}
}

multiLevelWriter定義了writers屬性，它也實現了LevelWriter接口，其Write及WriteLevel方法均是遍歷writers挨個執行對應操做；MultiLevelWriter方法經過levelWriterAdapter來適配io.Writer

實例

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!")
}

這裏使用zerolog.MultiLevelWriter來指定多個輸出

輸出

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

小結

LevelWriter接口內嵌了io.Writer接口，定義了WriteLevel方法；levelWriterAdapter內嵌了io.Writer屬性，實現了LevelWriter的WriteLevel方法，該方法內部經過io.Writer屬性的Write方法來輸出；SyncWriter方法經過levelWriterAdapter來適配io.Writer；MultiLevelWriter方法經過levelWriterAdapter來適配io.Writer。

doc

• zerolog