eslog : 🌈 slog.Handler that writes prettier logs

Package eslog implements a slog.Handler that writes prettier logs. Two modes are supported: pretty and json.

Supported logging levels:

• Trace
• Debug
• Info
• Warn
• Error
• Fatal

Pretty

Logging formatting in Pretty mode. In this mode, it's easy to navigate to the file position where the log was called.

JSON

Logging formatting in JSON mode.

Installation

go get github.com/eliofery/eslog

Usage

// Configures the logger with the specified settings.
config := eslog.Config{
    Level:     "info", // trace, debug, info, warn, error, fatal (info: default)
    AddSource: true,
    JSON:      false,
}

// Sets the logging level.
lvl := new(slog.LevelVar)
lvl.Set(config.Leveler())

// Creates a new instance of eslog with the configured settings.
logger := eslog.New(pretty.NewHandler(os.Stdout, &pretty.HandlerOptions{
    SlogOptions: &slog.HandlerOptions{
        Level:     lvl,
        AddSource: config.AddSource,
    },
    JSON: config.JSON,
}), lvl)

// Overrides the logging level.
logger.SetLevel(eslog.LevelTrace)
//logger.SetLevel(slog.LevelDebug)
//logger.SetLevel(slog.LevelInfo)
//logger.SetLevel(slog.LevelWarn)
//logger.SetLevel(slog.LevelError)
//logger.SetLevel(eslog.LevelFatal)

// Logs messages at different levels.
logger.Trace("Trace example", slog.Any("message", "trace message"))
logger.Debug("Debug example", slog.Any("message", "debug message"))
logger.Info("Info example", slog.Any("message", "info message"))
logger.Warn("Warn example", slog.Any("message", "warn message"))
logger.Error("Error example", slog.Any("message", "error message"))
logger.Fatal("Fatal example", slog.Any("message", "fatal message"))

Customize Attributes

ReplaceAttr can be used to alter or drop attributes. See slog.HandlerOptions for details.

lvl := new(slog.LevelVar)
lvl.Set(slog.LevelInfo)
	
eslog.New(pretty.NewHandler(os.Stdout, &pretty.HandlerOptions{
    SlogOptions: &slog.HandlerOptions{
        ReplaceAttr: func(_ []string, a slog.Attr) slog.Attr {
            switch a.Key {
            case slog.SourceKey:
                return func(a slog.Attr) slog.Attr {
                    source := a.Value.Any().(slog.Source)
    
                    pwd, err := os.Getwd()
                    if err != nil {
                        return a
                    }
    
                    relPath, err := filepath.Rel(pwd, source.File)
                    if err != nil {
                        return a
                    }
    
                    basePath := filepath.Base(relPath)
    
                    formattedPath := fmt.Sprintf("%s:%d", basePath, source.Line)
    
                    return slog.Attr{
                        Key:   a.Key,
                        Value: slog.StringValue(formattedPath),
                    }
                }(a)
            case slog.LevelKey:
                return func(a slog.Attr) slog.Attr {
                    l := a.Value.Any().(slog.Level)
                    a.Value = slog.StringValue(l.String())
    
                    return a
                }(a)
            case slog.TimeKey:
                return func(a slog.Attr) slog.Attr {
                    const timestampFormat = "2006-01-02 15:04:05.999999999 -0700 -07"
    
                    t, err := time.Parse(timestampFormat, a.Value.String())
                    if err != nil {
                        return a
                    }
    
                    formattedTime := t.Format(time.DateTime)
                    a.Value = slog.StringValue(formattedTime)
    
                    return a
                }(a)
            default:
                return a
            }
        },
    },
}), lvl)

Support for the standard package slog

You can still use methods from the standard package slog.

lvl := new(slog.LevelVar)
lvl.Set(eslog.LevelTrace)
	
// NewTextHandler
eslog.New(slog.NewTextHandler(os.Stdout, &slog.HandlerOptions{}), lvl)

// NewJSONHandler
eslog.New(slog.NewJSONHandler(os.Stdout, &slog.HandlerOptions{}), lvl)

Inspiration

I was inspired to write this package by the slog and tint.