revive/logging/logger.go

// Package logging provides a logger and related methods.
package logging

import (
	"io"
	"log/slog"
	"os"
)

const logFile = "revive.log"

var logger *slog.Logger

// GetLogger retrieves an instance of an application logger which outputs
// to a file if the debug flag is enabled
func GetLogger() (*slog.Logger, error) {
	if logger != nil {
		return logger, nil
	}

	debugModeEnabled := os.Getenv("DEBUG") != ""
	if !debugModeEnabled {
		// by default, suppress all logging output
		return slog.New(slog.NewTextHandler(io.Discard, nil)), nil // TODO: change to slog.New(slog.DiscardHandler) when we switch to Go 1.24
	}

	fileWriter, err := os.Create(logFile)
	if err != nil {
		return nil, err
	}

	logger = slog.New(slog.NewTextHandler(io.MultiWriter(os.Stderr, fileWriter), nil))

	logger.Info("Logger initialized", "logFile", logFile)

	return logger, nil
}