tint: 🌈 slog.Handler that writes tinted logs

About this fork

This package is a fork of the original lmittmann/tint package. This fork adds support for color expressions (in MemoANSI format) in log messages.

Overview

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/phplego/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 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 err, ok := a.Value.Any().(error); ok {
                aErr := tint.Err(err)
                aErr.Key = a.Key
                return aErr
            }
            return a
        },
    }),
)

Color Expressions

Color expression is a string that starts with @ followed by a color/background/boldness code and ends with {some text}. The format is @<color><bold><background>{text} for example @r!W{red bold on white background}. First symbol after @ is a color code, second symbol is an optional boldness flag (exclamation mark) and third symbol is an optional background color code.

// usage of color expressions
slog.Info("Example of @r{red color}")
slog.Info("Example of @R{bright red color}")
slog.Info("Example of @r!{red bold color}")
slog.Info("Example of @rW{red on white backgound}")
slog.Info("Example of @r!W{red bold on white backgound}")
slog.Info("Example of @*{Rainbow text}")

Supported color codes are:

Code	Color	Bright Variant Code	Bright Color
k	Black	K	Bright Black (Gray)
r	Red	R	Bright Red
g	Green	G	Bright Green
y	Yellow	Y	Bright Yellow
b	Blue	B	Bright Blue
m	Magenta	M	Bright Magenta
c	Cyan	C	Bright Cyan
w	White	W	Bright White

• * - Rainbow. Special color where each character has a different color.

See MemoANSI format for more details.

Automatically Enable Colors

Colors are enabled by default and can be disabled using the Options.NoColor attribute. To automatically enable colors based on the 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),
)