/// <summary>
        /// http下载文件
        /// </summary>
        /// <param name="url">下载文件地址</param>
        /// <returns></returns>
        public static Stream HttpDownload(string url)
        {
            using (var client = new WebClient())
            {
                string tempFile = Path.GetTempFileName();
                client.DownloadFile(url, tempFile);//下载临时文件
                Console.WriteLine("Using " + tempFile);
                return FileToStream(tempFile, true);
            }
        }
        /// <summary>
        /// 文件转流
        /// </summary>
        /// <param name="fileName">文件路径</param>
        /// <param name="isDelete">是否删除临时文件</param>
        /// <returns></returns>
        public static Stream FileToStream(string fileName, bool isDelete = false)
        {

            //打开文件

            FileStream fileStream = new FileStream(fileName, FileMode.Open, FileAccess.Read, FileShare.Read);

            // 读取文件的 byte[]

            byte[] bytes = new byte[fileStream.Length];

            fileStream.Read(bytes, 0, bytes.Length);

            fileStream.Close();

            // 把 byte[] 转换成 Stream

            Stream stream = new MemoryStream(bytes);
            if (isDelete)
            {
                File.Delete(fileName);//删除临时文件
            }
            return stream;

        }