package main

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

func main() {
	ctx, cancel := context.WithCancel(context.Background())

	// subscribe to SIGINT signals
	stopChan := make(chan os.Signal, 1)
	signal.Notify(stopChan, os.Interrupt, syscall.SIGTERM, syscall.SIGINT, syscall.SIGUSR2)

	mux := http.NewServeMux()

	mux.Handle("/", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		time.Sleep(10 * time.Second)
		_,_=io.WriteString(w, "Finished!")
	}))

	srv := &http.Server{
		Addr: ":8081",
		Handler: mux,
		BaseContext: func(_ net.Listener) context.Context { return ctx },
	}
	srv.RegisterOnShutdown(cancel)

	go func() {
		// service connections
		if err := srv.ListenAndServe(); err != nil {
			log.Printf("listen: %s\n", err)
		}
	}()

	<-stopChan // wait for SIGINT
	log.Println("Shutting down server...")

	// shut down gracefully, but wait no longer than 10 seconds before halting
	gracefulCtx, cancelShutdown := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancelShutdown()
	if err := srv.Shutdown(gracefulCtx); err != nil {
		log.Printf("shutdown error: %v\n", err)
		defer os.Exit(1)
		return
	} else {
		//app.Close() // !important 留意上下文位置
		log.Printf("gracefully stopped\n")
	}
	log.Println("Server gracefully stopped")

}