slogs

slogs

This is a wrapper around the stdlib Golang slog package that just creates a slog logger in some standard way, with a configurable log level.

Slog was introduced in Go 1.21, so that is the minimum required Go version to use this module.

Usage

package main

import "github.com/chia-network/go-modules/pkg/slogs"

func main() {
	// Init the logger with a log-level string (debug, info, warn, error)
	// defaults to "info" if empty or unsupported string 
	// not passing any logger options
	slogs.Init("info")

	// Logs a hello world message at the info level
	slogs.Logr.Info("hello world")

	// Logs an error message at the error level 
	slogs.Logr.Error("we received an error")
}

In a Cobra/Viper CLI app this might look more like:

package cmd

import (
	"log"
	
	"github.com/spf13/cobra"
	"github.com/spf13/viper"
	"github.com/chia-network/go-modules/pkg/slogs"
)

var rootCmd = &cobra.Command{
	Use:   "cmd",
	Short: "Short help message for cmd",

	Run: func(cmd *cobra.Command, args []string) {
		// Init logger
		slogs.Init(viper.GetString("log-level"))

		// Application logic below
	},
}

func Execute() {
	cobra.CheckErr(rootCmd.Execute())
}

func init() {
	rootCmd.PersistentFlags().String("log-level", "info", "The log-level for the application, can be one of info, warn, error, debug.")
	err := viper.BindPFlag("log-level", rootCmd.PersistentFlags().Lookup("log-level"))
	if err != nil {
		log.Fatalln(err.Error()) // Have to log with standard logger until the slog logger is initialized
	}
}

Logger Options

Source contexts

Source context tells you the position in your code that created a log line. This is disabled by default, but can be enabled when initializing this package as follows:

slogs.Init("info", slogs.WithSourceContext(true))

Writer

The default logger's writer sends logs to stdout. you can change this when initializing this package as follows:

slogs.Init("info", slogs.WithWriter(io.Discard))

This example uses io.Discard which sends logs to /dev/null but any other interface that implements the standard Write method will work, such as os.Stderr.

JSON output

The default logger outputs logs in text format. To output logs in JSON format instead, enable it when initializing:

slogs.Init("info", slogs.WithJSONOutput())