聊聊zerolog的Formatter

// Formatter transforms the input into a formatted string.
type Formatter func(interface{}) string

type ConsoleWriter struct {
    // Out is the output destination.
    Out io.Writer

    // NoColor disables the colorized output.
    NoColor bool

    // TimeFormat specifies the format for timestamp in output.
    TimeFormat string

    // PartsOrder defines the order of parts in output.
    PartsOrder []string

    FormatTimestamp     Formatter
    FormatLevel         Formatter
    FormatCaller        Formatter
    FormatMessage       Formatter
    FormatFieldName     Formatter
    FormatFieldValue    Formatter
    FormatErrFieldName  Formatter
    FormatErrFieldValue Formatter
}

// writePart appends a formatted part to buf.
func (w ConsoleWriter) writePart(buf *bytes.Buffer, evt map[string]interface{}, p string) {
    var f Formatter

    switch p {
    case LevelFieldName:
        if w.FormatLevel == nil {
            f = consoleDefaultFormatLevel(w.NoColor)
        } else {
            f = w.FormatLevel
        }
    case TimestampFieldName:
        if w.FormatTimestamp == nil {
            f = consoleDefaultFormatTimestamp(w.TimeFormat, w.NoColor)
        } else {
            f = w.FormatTimestamp
        }
    case MessageFieldName:
        if w.FormatMessage == nil {
            f = consoleDefaultFormatMessage
        } else {
            f = w.FormatMessage
        }
    case CallerFieldName:
        if w.FormatCaller == nil {
            f = consoleDefaultFormatCaller(w.NoColor)
        } else {
            f = w.FormatCaller
        }
    default:
        if w.FormatFieldValue == nil {
            f = consoleDefaultFormatFieldValue
        } else {
            f = w.FormatFieldValue
        }
    }

    var s = f(evt[p])

    if len(s) > 0 {
        buf.WriteString(s)
        if p != w.PartsOrder[len(w.PartsOrder)-1] { // Skip space for last part
            buf.WriteByte(' ')
        }
    }
}

func formatDemo() {
    output := zerolog.ConsoleWriter{Out: os.Stdout, TimeFormat: time.RFC3339}
    output.FormatLevel = func(i interface{}) string {
        return strings.ToUpper(fmt.Sprintf("| %-6s|", i))
    }
    output.FormatMessage = func(i interface{}) string {
        return fmt.Sprintf("***%s****", i)
    }
    output.FormatFieldName = func(i interface{}) string {
        return fmt.Sprintf("%s:", i)
    }
    output.FormatFieldValue = func(i interface{}) string {
        return strings.ToUpper(fmt.Sprintf("%s", i))
    }

    log := zerolog.New(output).With().Timestamp().Logger()
    log.Info().Str("foo", "bar").Msg("Hello World")
}

2021-01-06T23:16:42+08:00 | INFO  | ***Hello World**** foo:BAR