使用Golang的Context管理上下文的方法

func main(){
  mux:=http.NewServeMux()
  mux.HandleFunc("/",StatusHandler)
  mux.HandleFunc("/login",LoginHandler)
  mux.HandleFunc("/logout",LogoutHandler)
  contextedMux:=AddContextSupport(mux)
  log.Fatal(http.ListenAndServe(":8080",contextedMux))
}

func AddContextSupport(next http.Handler)http.Handler{
  return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
    log.Println(r.Method, "-", r.RequestURI)
    cookie, _ := r.Cookie("username")
    if cookie != nil {
      ctx := context.WithValue(r.Context(), "username", cookie.Value)
      // WithContext returns a shallow copy of r with its context changed
      // to ctx. The provided ctx must be non-nil.
      next.ServeHTTP(w, r.WithContext(ctx))
    } else {
      next.ServeHTTP(w, r)
    }
  })
}

func LoginHandler(w http.ResponseWriter,r *http.Request){
  expitation := time.Now().Add(24*time.Hour)
  var username string
  if username=r.URL.Query().Get("username");username==""{
    username = "guest"
  }
  cookie:=http.Cookie{Name:"username",Value:username,Expires:expitation}
  http.SetCookie(w,&cookie)
}

func LogoutHandler(w http.ResponseWriter, r *http.Request) {
  expiration := time.Now().AddDate(0, 0, -1)
  cookie := http.Cookie{Name: "username", Value: "alice_cooper@gmail.com", Expires: expiration}
  http.SetCookie(w, &cookie)
}

func StatusHandler(w http.ResponseWriter,r *http.Request){

  if username:=r.Context().Value("username"); username!=nil{
    w.WriteHeader(http.StatusOK)
    w.Write([]byte("Hi username:"+username.(string)+"\n"))
  }else{
    w.WriteHeader(http.StatusNotFound)
    w.Write([]byte("Not Logged in"))
  }
}

mux.HandleFunc("/longjob",jobWithCancelHandler)

func longRunningCalculation(timeCost int)chan string{

  result:=make(chan string)
  go func (){
    time.Sleep(time.Second*(time.Duration(timeCost)))
    result<-"Done"
  }()
  return result
}
func jobWithCancelHandler(w http.ResponseWriter, r * http.Request){
  var ctx context.Context
  var cancel context.CancelFunc
  var jobtime string
  if jobtime=r.URL.Query().Get("jobtime");jobtime==""{
    jobtime = "10"
  }
  timecost,err:=strconv.Atoi(jobtime)
  if err!=nil{
    timecost=10
  }
  log.Println("Job will cost : "+jobtime+"s")
  ctx,cancel = context.WithCancel(r.Context())
  defer cancel()

  go func(){
    time.Sleep(5*time.Second)
    cancel()
  }()

  select{
  case <-ctx.Done():
    log.Println(ctx.Err())
    return
  case result:=<-longRunningCalculation(timecost):
    io.WriteString(w,result)
  }
  return
}