go http server with graceful shutdown

http-server-shutdown.go

package main

import (
	"context"
	"flag"
	"log"
	"net/http"
	"os"
	"os/signal"
	"time"
)

func main() {
	log.SetFlags(0)

	var listenAddress = flag.String("listen", ":8000", "Listen address.")

	flag.Parse()

	if flag.NArg() != 0 {
		flag.Usage()
		log.Fatalf("\nERROR You MUST NOT pass any positional arguments")
	}

	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		log.Printf("HTTP %s %s%s\n", r.Method, r.Host, r.URL)

		if r.URL.Path != "/" {
			http.Error(w, "Not Found", http.StatusNotFound)
			return
		}

		w.Header().Set("Content-Type", "text/plain")
		w.Write([]byte(time.Now().Local().Format(time.RFC1123Z)))
	})

	log.Printf("Listening at http://%s", *listenAddress)

	httpServer := http.Server{
		Addr: *listenAddress,
	}

	idleConnectionsClosed := make(chan struct{})
	go func() {
		sigint := make(chan os.Signal, 1)
		signal.Notify(sigint, os.Interrupt)
		<-sigint
		if err := httpServer.Shutdown(context.Background()); err != nil {
			log.Printf("HTTP Server Shutdown Error: %v", err)
		}
		close(idleConnectionsClosed)
	}()

	if err := httpServer.ListenAndServe(); err != http.ErrServerClosed {
		log.Fatalf("HTTP server ListenAndServe Error: %v", err)
	}

	<-idleConnectionsClosed

	log.Printf("Bye bye")
}