[Go Starter Template] For new projects, this gives logging and a nice testable structure based on blog posts by Matt Ryer #go #template

main.go

package main

import (
	"errors"
	"flag"
	"fmt"
	"io"
	"os"
	"strings"
	"time"

	"github.com/rs/zerolog"
	"github.com/rs/zerolog/log"
)

const (
	// exitFail is the exit code if the program
	// fails.
	exitFail = 1
)

func main() {
	if err := run(os.Args, os.Stdout); err != nil {
		fmt.Fprintf(os.Stderr, "%s\n", err)
		os.Exit(exitFail)
	}
}

// Run handles the arguments being passed in from main, and allows us to run tests against the loading of the code much more easily than embedding all the startup logic in main().
// This is based on Matt Ryers post: https://pace.dev/blog/2020/02/12/why-you-shouldnt-use-func-main-in-golang-by-mat-ryer.html
func run(args []string, stdout io.Writer) error {
	if len(args) == 0 {
		return errors.New("no arguments")
	}
	for _, value := range args[1:] {
		fmt.Fprintf(stdout, "Running with flag: %s\n", value)
	}
	InitLogger()
	zerolog.SetGlobalLevel(zerolog.InfoLevel)

	debug := flag.Bool("debug", false, "sets log level to debug")
	flag.Parse()
	if *debug {
		zerolog.SetGlobalLevel(zerolog.DebugLevel)
	}
	return nil
}

// InitLogger sets up the logger magic
// By default this is only configured to do pretty console output.
// JSON structured logs are also possible, but not in my default template layout at this time.
func InitLogger() {
	output := zerolog.ConsoleWriter{Out: os.Stdout, TimeFormat: time.RFC3339}
	log.Logger = log.With().Caller().Logger().Output(zerolog.ConsoleWriter{Out: os.Stderr})

	output.FormatLevel = func(i interface{}) string {
		return strings.ToUpper(fmt.Sprintf("| %-6s|", i))
	}
	output.FormatMessage = func(i interface{}) string {
		return fmt.Sprintf("%s", i)
	}
	output.FormatFieldName = func(i interface{}) string {
		return fmt.Sprintf("%s:", i)
	}
	output.FormatFieldValue = func(i interface{}) string {
		return strings.ToUpper(fmt.Sprintf("%s", i))
	}
	log.Info().Msg("logger initialized")
}