go 使用单例创建client，并复用

var (
   httpClient *http.Client
   once   sync.Once
)

func CreateHTTPClient() *http.Client {
   // 使用单例创建client
   once.Do(func() {
      httpClient = &http.Client{
         Transport: &http.Transport{
            DialContext: (&net.Dialer{
               Timeout:   30 * time.Second,
               KeepAlive: 30 * time.Second,
            }).DialContext,
            MaxIdleConns:        50000,              // 最大连接数,默认0无穷大
            MaxIdleConnsPerHost: 50000,              // 对每个host的最大连接数量(MaxIdleConnsPerHost<=MaxIdleConns)
            IdleConnTimeout:     30 * time.Second, // 多长时间未使用自动关闭连接
            TLSClientConfig: &tls.Config{InsecureSkipVerify: true},
            TLSHandshakeTimeout:3*time.Second,
            ExpectContinueTimeout: 1 * time.Second,
         },
         Timeout:3 *time.Millisecond,
      }
   })
   return httpClient
}

func HttpsPost(url string,stu []byte,body *[]byte)[]byte{
   client := CreateHTTPClient()
   reader := bytes.NewReader(stu)
   request,err := http.NewRequest("POST", url, reader)
   if err !=nil{
      return nil
   }
   request.Header.Set("Content-Type", "x-protobuf")
   request.Header.Set("Connection", "Keep-Alive")
   response,err := client.Do(request)
   if err !=nil{
      return nil
   }
   *body,_ =ioutil.ReadAll(response.Body)
   defer response.Body.Close()  
   return *body   
}