context

main.go

package main

import (
	"fmt"
	"net/http"
	"strconv"
	"time"
)

type handler struct{}

func (h *handler) ServeHTTP(w http.ResponseWriter, req *http.Request) {
	fmt.Printf("%s %s\n", req.Method, req.URL)

	t, err := strconv.Atoi(req.URL.Query().Get("t"))
	if err != nil {
		t = 5
	}

	ch := make(chan error, 1)
	ctx := req.Context()

	go func() {
		time.Sleep(time.Duration(t) * time.Second)
		fmt.Printf("%+v\n", "done")
		ch <- nil
	}()

	w.WriteHeader(http.StatusOK)
	select {
	case <-ch:
		w.Write([]byte((fmt.Sprintf("%d seconds sleeped", t))))
		fmt.Printf("%+v\n", "sleeped")
	case <-ctx.Done():
		w.Write([]byte("cancelled" + ctx.Err().Error()))
		fmt.Printf("cancelled %+v\n", ctx.Err())
	}
	return
}

func main() {
	s := &http.Server{
		Addr:              ":8080",
		ReadTimeout:       3 * time.Second,
		WriteTimeout:      3 * time.Second,
		ReadHeaderTimeout: 3 * time.Second,
		Handler:           &handler{},
		// Handler:      http.TimeoutHandler(&handler{}, 3*time.Second, "request timed out"),
	}

	s.ListenAndServe()
}