golang http下載文件

func LoadFile(w http.ResponseWriter, r *http.Request, p httprouter.Params) {
	url:= p.ByName("url")
	file, err:= os.Open("./" + url)
	if err!= nil {
		httputil.WriteErrorResponse(w, "文件不存在")
		return
	}
	defer file.Close()
	buff, _ := ioutil.ReadAll(file)
	w.Write(buff)
}