asp.net断点续传

using System;
    using System.Data;
    using System.Configuration;
    using System.Collections;
    using System.Web;
    using System.Web.Security;
    using System.Web.UI;
    using System.Web.UI.WebControls;
    using System.Web.UI.WebControls.WebParts;
    using System.Web.UI.HtmlControls;
    using System.IO;
    public partial class DFile : System.Web.UI.Page
    {
    protected void Page_Load(object sender, EventArgs e)
    {
    }
    protected void LinBtnDFile_Click(object sender, EventArgs e)
    {
    // 创建一比特数组
    byte[] buffer = new Byte[10240];
    // 指定要下载文件的路径.
    string filePath = @"D:\爱智旮旯.rar";
    // 或取文件名包括扩展名
    string fileName = Path.GetFileName(filePath);
    Stream fileStream = null;
    try
    {
    // 打开文件
    fileStream = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.Read);
    Response.Clear();
    // 获取文件的大小
    long fileSize = fileStream.Length;
    long sum = 0;
    if (Request.Headers["Range"] != null)
    {
    Response.StatusCode = 206; // 表示返回到客户端的 HTTP 输出状态的整数。默认值为 200。
    sum = long.Parse(Request.Headers["Range"].Replace("bytes=", "").Replace("-", ""));
    }
    if (sum != 0)
    {
    Response.AddHeader("Content-Range", "bytes " + sum.ToString() + "-" + ((long)(fileSize)).ToString() + "/" + fileSize.ToString());
    }
    // 获取部分http头信息
    Response.AddHeader("Content-Length", ((long)(fileSize - sum)).ToString());
    Response.ContentType = "application/octet-stream";
    //获取文件来源
    Response.AddHeader("Content-Disposition", "attachment; filename=" + HttpUtility.UrlEncode(Request.ContentEncoding.GetBytes(fileName)));
    // Response.Flush();
    fileStream.Position = sum; //设置当前流位置
    fileSize = fileSize - sum;
    // 当文件大小大于0是进入循环
    while (fileSize > 0)
    {
    // 判断客户端是否仍连接在服务器
    if (Response.IsClientConnected)
    {
    // 获取缓冲区中的总字节数.
    int length = fileStream.Read(buffer, 0, 10240);
    // 写入数据
    Response.OutputStream.Write(buffer, 0, length);
    // 将缓冲区的输出发送到客户端
    Response.Flush();
    buffer = new Byte[10240];
    fileSize = fileSize - length;
    }
    else
    {
    //当用户断开后退出循环
    fileSize = -1;
    }
    }
    }
    catch (Exception ex)
    {
    Response.Write("Error : " + ex.Message);
    }
    finally
    {
    if (fileStream != null)
    {
    //关闭文件
    fileStream.Close();
    }
    Response.End();
    }
    }
    }