关于golang:聊聊zerolog的LevelWriter

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本文次要钻研一下 zerolog 的 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 接口内嵌了 io.Writer 接口，定义了 WriteLevel 办法

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 内嵌了 io.Writer 属性，实现了 LevelWriter 的 WriteLevel 办法，该办法外部通过 io.Writer 属性的 Write 办法来输入

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

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

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!")
}

这里应用 zerolog.MultiLevelWriter 来指定多个输入

输入

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

LevelWriter 接口内嵌了 io.Writer 接口，定义了 WriteLevel 办法；levelWriterAdapter 内嵌了 io.Writer 属性，实现了 LevelWriter 的 WriteLevel 办法，该办法外部通过 io.Writer 属性的 Write 办法来输入；SyncWriter 办法通过 levelWriterAdapter 来适配 io.Writer；MultiLevelWriter 办法通过 levelWriterAdapter 来适配 io.Writer。