golang： multiple http.writeHeader calls

這是一個建立於 的文章，其中的資訊可能已經有所發展或是發生改變。背景：golang的http服務，讀取檔案，提供給client下載時候。出現 multiple http.writeHeader calls 錯誤。

func DownloadFile(w http.ResponseWriter, r *http.Request, sequence uint64, userid string) {    userkey := userid    filename := r.FormValue("filename")    if len(userkey) <= 0 || len(filename) <= 0 {        //........    }    fp := fmt.Sprintf("%s%s/%s", g_sc.Rootdir, userkey, filename)    fd, err := os.Open(fp)    if err == nil {        defer fd.Close()        buf, err := ioutil.ReadAll(fd)        if err != nil {            //.........        } else {            size := len(buf)            w.Header().Add("Content-Length", fmt.Sprintf("%d", size))            fmt.Fprint(w, string(buf))        }    }}

 

問題出現在這幾行代碼：

size := len(buf)
w.Header().Add("Content-Length", fmt.Sprintf("%d", size))
fmt.Fprint(w, string(buf))

 可以做如下修改： 

buf := new(bytes.Buffer)buf.Write(...) if err {  // you can use http.Error here, no response has been written yet  http.Error(w, err.String, http.StatusInternalServerError)  return} if err := buf.WriteTo(w); err != nil {  log.Printf("WriteTo: %v", err)  // you can not use http.Error here anymore. So just log the message (e.g. "broken pipe...")}

 

 或者注釋這兩行代碼 //size := len(buf)
 //w.Header().Add("Content-Length", fmt.Sprintf("%d", size))
fmt.Fprint(w, string(buf))