tint: 🌈 slog.Handler that writes tinted logs

Package tint implements a zero-dependency slog.Handler that writes tinted (colorized) logs. Its output format is inspired by the zerolog.ConsoleWriter and slog.TextHandler.

The output format can be customized using Options which is a drop-in replacement for slog.HandlerOptions.

go get github.com/lmittmann/tint

Usage

w := os.Stderr

// Create a new logger
logger := slog.New(tint.NewHandler(w, nil))

// Set global logger with custom options
slog.SetDefault(slog.New(
    tint.NewHandler(w, &tint.Options{
        Level:      slog.LevelDebug,
        TimeFormat: time.Kitchen,
    }),
))

Customize Attributes

ReplaceAttr can be used to alter or drop attributes. If set, it is called on each non-group attribute before it is logged. See slog.HandlerOptions for details.

// Create a new logger with a custom TRACE level:
const LevelTrace = slog.LevelDebug - 4

w := os.Stderr
logger := slog.New(tint.NewHandler(w, &tint.Options{
    Level: LevelTrace,
    ReplaceAttr: func(groups []string, a slog.Attr) slog.Attr {
        if a.Key == slog.LevelKey && len(groups) == 0 {
            level, ok := a.Value.Any().(slog.Level)
            if ok && level <= LevelTrace {
                return tint.Attr(13, slog.String(a.Key, "TRC"))
            }
        }
        return a
    },
}))

// Create a new logger that doesn't write the time
w := os.Stderr
logger := slog.New(
    tint.NewHandler(w, &tint.Options{
        ReplaceAttr: func(groups []string, a slog.Attr) slog.Attr {
            if a.Key == slog.TimeKey && len(groups) == 0 {
                return slog.Attr{}
            }
            return a
        },
    }),
)

// Create a new logger that writes all errors in red
w := os.Stderr
logger := slog.New(
    tint.NewHandler(w, &tint.Options{
        ReplaceAttr: func(groups []string, a slog.Attr) slog.Attr {
            if a.Value.Kind() == slog.KindAny {
                if _, ok := a.Value.Any().(error); ok {
                    return tint.Attr(9, a)
                }
            }
            return a
        },
    }),
)

Automatically Enable Colors

Colors are enabled by default. Use the Options.NoColor field to disable color output. To automatically enable colors based on terminal capabilities, use e.g., the go-isatty package:

w := os.Stderr
logger := slog.New(
    tint.NewHandler(w, &tint.Options{
        NoColor: !isatty.IsTerminal(w.Fd()),
    }),
)

Windows Support

Color support on Windows can be added by using e.g., the go-colorable package:

w := os.Stderr
logger := slog.New(
    tint.NewHandler(colorable.NewColorable(w), nil),
)