最近遇到的一个项目，附件在A服务器，对外是B服务器，A与B服务器可以内网通信，但是A服务器不对外，就需要用到B服务器的对外访问地址浏览附件与文件，参考了部分网上的代码，附上代码。

PS：不支持加速器下载

 /// <summary>

 /// 异步下载

 /// </summary>

 /// <param name="sender"></param>

 /// <param name="e"></param>

 private async void FileDownloadAsync(string url)

 {

 //开启一个异步线程

 await System.Threading.Tasks.Task.Run(async () =>

 {

 long downloadSize = 0;//已经下载大小

 long downloadSpeed = 0;//下载速度

 

 using (HttpClient http = new HttpClient())

 {

 var httpResponseMessage = await http.GetAsync(url, HttpCompletionOption.ResponseHeadersRead);//发送请求

 var contentLength = httpResponseMessage.Content.Headers.ContentLength; //文件大小 

 string contentType = httpResponseMessage.Content.Headers.ContentType.MediaType??MimeMapping.GetMimeMapping(url);

 string fileName = httpResponseMessage.Content.Headers.ContentDisposition!=null?httpResponseMessage.Content.Headers.ContentDisposition.FileName:Path.GetFileName(url);

 //兼容各种URL文件

 if (fileName.IsNull())

 fileName = Path.GetFileName(url);

 

 using (var stream = await httpResponseMessage.Content.ReadAsStreamAsync())

 {

 var readLength = 102400;//100K

 byte[] bytes = new byte[readLength];

 int writeLength;

 var beginSecond = DateTime.Now.Second;//当前时间秒

 

 Response.Clear();

 Response.ContentType = "application/octet-stream"; //二进制流

 Response.AddHeader("Content-Disposition", "attachment; filename=" + HttpUtility.UrlEncode(fileName, System.Text.Encoding.UTF8));//下载保存的文件名

 

 Response.AddHeader("Content-Length", contentLength.HasValue?contentLength.Value.ToString():"0");//文件总大小

 while ((writeLength = stream.Read(bytes, 0, readLength)) > 0)

 {

 

 if (Response.IsClientConnected)

 {

 Response.OutputStream.Write(bytes, 0, writeLength);

 Response.Flush();//如果客户端 暂停下载时，这里会阻塞。

 }

 

 downloadSize += writeLength;

 downloadSpeed += writeLength;

 }

 Response.Close();

 }

 }

 });

 }