feat req: log/slog: adding support for quiet log level

[Nicolas-Peiffer]

Proposal Details

In some use cases, you want to suppress (discard) all the logs outputs. However, log/slog does not support this quiet log level, but you can create a custom one implementing the quiet behavior.

My original InitLogger method without support for quiet

This is my original InitLogger method, with the supported log/slog levels debug, info, warn, error

func InitLogger(level string) error {
	var logLevel slog.Level

	switch level {
	case "debug":
		logLevel = slog.LevelDebug
	case "info":
		logLevel = slog.LevelInfo
	case "warn":
		logLevel = slog.LevelWarn
	case "error":
		logLevel = slog.LevelError
	default:
		return fmt.Errorf("invalid log level: %s", level)
	}

	handler := slog.NewTextHandler(os.Stdout, &slog.HandlerOptions{Level: logLevel})
	slog.SetDefault(slog.New(handler))

	slog.Info("Logger initialized", "log-level", level)
	return nil
}

I call the method like this, for example in my cobra CLI:

// RootCmd represents the base command when called without any subcommands
var RootCmd = &cobra.Command{
	Use:   [...]
	Run: func(cmd *cobra.Command, args []string) {
		logger.InitLogger(LogLevel)

And I set the log level thanks to a cobra flag --log-level=info|debug...

func init() {
	// Here you will define your flags and configuration settings.
	// Cobra supports persistent flags, which, if defined here,
	// will be global for your application.
	// rootCmd.PersistentFlags().StringVar(&cfgFile, "config", "", "config file (default is $HOME/.app.yaml)")
	RootCmd.PersistentFlags().StringVar(&LogLevel, "log-level", "info", "set the log level (debug, info, warn, error)")

My workaround: adding a custom quiet log level

The workaround is fine. It is just a bit less elegant since I need to define slog.NewTextHandler for each 5 cases of the switch case. I do not know if I can achieve something better.

// InitLogger initializes the logger with the given level. Valid log levels are
// "debug", "info", "warn", "error", and "quiet". If the log level is invalid,
// an error is returned.
func InitLogger(level string) error {
	var handler slog.Handler

	switch level {
	case "debug":
		handler = slog.NewTextHandler(os.Stdout, &slog.HandlerOptions{Level: slog.LevelDebug})
	case "info":
		handler = slog.NewTextHandler(os.Stdout, &slog.HandlerOptions{Level: slog.LevelInfo})
	case "warn":
		handler = slog.NewTextHandler(os.Stdout, &slog.HandlerOptions{Level: slog.LevelWarn})
	case "error":
		handler = slog.NewTextHandler(os.Stdout, &slog.HandlerOptions{Level: slog.LevelError})
	case "quiet":
		// Create a logger with a nil handler
		// Use io.Discard to suppress all output
		handler = slog.NewTextHandler(io.Discard, nil)
	default:
		return fmt.Errorf("invalid log level: %s", level)
	}

	// Set the logger to use the chosen handler
	slog.SetDefault(slog.New(handler))

	slog.Info("Logger initialized", "log-level", level)
	return nil
}

I believe it should be possible to add this quiet log level somewhere in the file src/log/slog/level.go.

But I am not a Golang contributor, and I do not know how to implement this.

cc @jba , since you made the proposal #56345, you might have an opinion or you migh know who could be interested.

I seem to be duplicating #62005
I missed it while searching the current issues.

[gabyhelp]

Related Issues and Documentation

• log/slog: enable setting level on default log.Logger #62418 (closed)
• proposal: log/slog: add `slog.DiscardHandler` #62005
• Package slog > type Level ¶ 1.21 > func SetLogLoggerLevel ¶ 1.22

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[Nicolas-Peiffer]

closing, duplicate #62005