# golang traffic shaving

模擬 time.Sleep(2 * time.Second)模擬server來不及處理這個request
假設 ddos 攻擊runtime.NumGoroutine() 可以做削峰，也可以防止ddos
smallPool = make(chan struct{}, 100)
也可為我們的server做buffer

package main

import (
	"fmt"
	"io/ioutil"
	"net/http"
	"runtime"
	"strconv"
	"time"
)

var largePool chan struct{}
var smallPool chan struct{}
var a = 0

//http://localhost:8000/?parameter=value&also=another
func main() {
    	smallPool = make(chan struct{}, 100)
    	http.HandleFunc("/endpoint-1", handler)
		http.ListenAndServe(":8080", nil)
}


func handler(w http.ResponseWriter, r *http.Request) {
	b, err := ioutil.ReadAll(r.Body)
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}
	fmt.Println("all nowgoroutine :", runtime.NumGoroutine())
	go func() {

		smallPool <- struct{}{}
		defer func() { <-smallPool }() // Let everyone that we are done
		fmt.Println("working!")
		time.Sleep(2 * time.Second)

		fmt.Println("work done")
		processImage(b)
	}()

	a += 1
	if runtime.NumGoroutine() < 20 {
		w.Write([]byte("msg" + strconv.Itoa(a)))
		w.WriteHeader(http.StatusAccepted)
	} else {

		w.WriteHeader(http.StatusNotFound)
		return

	}

}