关于pos请求的疑问？？

~~~ func postFile(filename string, targetURL string) error { bodyBuf := &bytes.Buffer{} bodyWriter := multipart.NewWriter(bodyBuf)//这一步不是很懂？？ //关键的一步操作 _, err := bodyWriter.CreateFormFile("file", filename) len := len(bodyBuf.Bytes()) buf1 := &bytes.Buffer{} buf1.Write(bodyBuf.Bytes()[0:len])//这是什么在干什么？？？ bodyWriter.Close() buf2 := &bytes.Buffer{} buf2.Write(bodyBuf.Bytes()[len:]) //这样不会是空的吗？？ //打开文件句柄操作 fh, err := os.Open(filename) if err != nil { flog.LOG_ERROR("can not opening file") return err } defer fh.Close() contentType := bodyWriter.FormDataContentType() mr := io.MultiReader(buf1, fh, buf2) //将其串联 //mr := io.MultiReader(buf1, fh, buf2) resp, err := http.Post(targetURL, contentType, mr) if err != nil { return err } defer resp.Body.Close() if resp.StatusCode != 200 { return nil } return nil } ~~~ ~~~ func HttpPost(targetUrl string, filename string) error { bodyBuf := &bytes.Buffer{} bodyWriter := multipart.NewWriter(bodyBuf) //关键的一步操作 fileWriter, err := bodyWriter.CreateFormFile("file", filename) //创建表头 if err != nil { fmt.Println("error writing to buffer") return err } //fmt.Println("url:", targetUrl) //打开文件句柄操作 fh, err := os.Open(filename) if err != nil { fmt.Println("error opening file") return err } _, err = io.Copy(fileWriter, fh) if err != nil { return err } contentType := bodyWriter.FormDataContentType()//得到类型 bodyWriter.Close() //bodyBuf resp, err := http.Post(targetUrl, contentType, bodyBuf) if err != nil { fmt.Println(err) return err } defer resp.Body.Close() resp_body, err := ioutil.ReadAll(resp.Body) if err != nil { return err } fmt.Println(resp.Status) fmt.Println(string(resp_body)) return nil } ~~~ 第一段代码比第二段怎么快这么多？？？ 第一段代码buf1、buf2是干什么的