gocustomurls/main.go

package main

import (
	"context"
	"errors"
	"flag"
	"fmt"
	"log"
	"net/http"
	"os"
	"os/signal"
	"path/filepath"
	"strconv"
	"syscall"
	"time"
)

var errorLog *log.Logger = log.New(os.Stderr, "", log.LstdFlags)

// const (
// 	DEFAULT_RULES_FILE string = "/var/lib/gocustomurls/rules.json"
// 	DEFAULT_LOG_FILE   string = "/var/log/gocustomurls/app.log"
// )

// flagsSet returns a set of all the flags what were actually set on the
// command line.
func flagsSet(flags *flag.FlagSet) map[string]bool {
	s := make(map[string]bool)
	flags.Visit(func(f *flag.Flag) {
		s[f.Name] = true
	})
	return s
}

// generateDefaults - generate the default values for the rules.json and log files
func generateDefaults(rulesfp string, logfp string) (string, string, error) {
	var newlogfp, newrulesfp string
	var err error
	newlogfp = logfp
	newrulesfp = rulesfp
	if len(newrulesfp) == 0 {
		dir, err := os.UserConfigDir()
		if err != nil {
			return newrulesfp, newlogfp, err
		}
		newrulesfp = filepath.Join(dir, "gocustomcurls", "rules.json")
	}
	if len(newlogfp) == 0 {
		dir, err := os.UserHomeDir()
		if err != nil {
			return newrulesfp, newlogfp, err
		}
		newlogfp = filepath.Join(dir, ".gocustomurls", "logs", "app.log")
	}
	return newrulesfp, newlogfp, err
}

// isValidPort returns true if the port is valid
// following the RFC https://datatracker.ietf.org/doc/html/rfc6056#section-2.1
func isValidPort(port int) bool {
	return port > 0 && port < 65535
}

func main() {
	programName := os.Args[0]
	// errorLog = log.New(os.Stderr, "", log.LstdFlags)

	flags := flag.NewFlagSet(os.Args[0], flag.ExitOnError)
	flags.Usage = func() {
		out := flags.Output()
		fmt.Fprintf(out, "Usage: %v [flags]\n\n", programName)
		fmt.Fprint(out, "  This utility serves vanity urls for the go get/install command.\n")
		fmt.Fprint(out, "  By default, the server listens on localhost:7070.\n")
		flags.PrintDefaults()
	}

	portFlag := flags.String("port", "7070", "Optional. Default port is 7070. Port to listen to")
	rulesFileFlag := flags.String("config", "", "Optional. Contains go-import mapping")
	logFileFlag := flags.String("logfile", "", "Optional. Default log file")
	flags.Parse(os.Args[1:])

	if len(flags.Args()) > 1 {
		errorLog.Println("Error: too many command-line arguments")
		flags.Usage()
		os.Exit(1)
	}

	allSetFlags := flagsSet(flags)

	var port string
	if allSetFlags["port"] {
		port = *portFlag
	} else {
		port = "7070"
	}

	p, err := strconv.Atoi(port)
	if err != nil {
		errorLog.Println(err)
		os.Exit(1)
	}

	if !isValidPort(p) {
		errorLog.Println(fmt.Errorf("provided port (%d) is not valid", p))
		os.Exit(1)
	}

	var rulesFile string

	if allSetFlags["config"] {
		rulesFile = *rulesFileFlag
	}

	var logFile string
	if allSetFlags["logFile"] {
		logFile = *logFileFlag
	}

	rFile, lFile, err := generateDefaults(logFile, rulesFile)
	if err != nil {
		errorLog.Println(err)
		os.Exit(1)
	}

	// load rules mapping
	c := &Config{}
	err = c.LoadMappingFile(rFile)
	if err != nil {
		errorLog.Println(err)
		os.Exit(1)
	}
	l, err := newFileLogger(lFile)
	if err != nil {
		errorLog.Println(err)
		os.Exit(1)
	}

	app := &Application{
		Config: c,
		Log:    l,
	}
	srv := app.Setup(port)

	// For graceful shutdowns
	go func() {
		app.Log.logger.Printf("%s Starting\n", getCurrentDate())
		err := srv.ListenAndServe()
		if !errors.Is(err, http.ErrServerClosed) {
			errorLog.Printf("HTTP Server error: %+v\n", err)
			os.Exit(1)
		}
		app.Log.logger.Printf("%s Stopped serving new connections.\n", getCurrentDate())
	}()

	sigChan := make(chan os.Signal, 1)
	signal.Notify(sigChan, syscall.SIGINT, syscall.SIGTERM)
	<-sigChan

	shutdownCtx, shutdownRelease := context.WithTimeout(context.Background(), 10*time.Second)
	defer shutdownRelease()

	if err := srv.Shutdown(shutdownCtx); err != nil {
		errorLog.Printf("HTTP shutdown error: %+v\n", err)
		os.Exit(1)
	}
	app.Log.logger.Printf("%s Graceful shutdown complete.\n", getCurrentDate())
}