多线程 断点续传

Stream iStream = null;
byte[] buffer = new Byte[10240];// 缓冲区块10K bytes :
int length;            
long dataToRead;           
string filepath = @"E:\software\SQL Server 2000 Personal Edition.ISO";
string filename = System.IO.Path.GetFileName(filepath);
try
{
    // 打开文件

    iStream = new FileStream(filepath, FileMode.Open,FileAccess.Read, FileShare.Read);
    Response.Clear();
    dataToRead = iStream.Length;
    long p = 0;
    if (Request.Headers["Range"] != null)
    {
        Response.StatusCode = 206;
        p = long.Parse(Request.Headers["Range"].Replace("bytes=", "").Replace("-", ""));
    }
    if (p != 0)
    {
        Response.AddHeader("Content-Range", "bytes " + p.ToString() + "-" + ((long)(dataToRead - 1)).ToString() + "/" + dataToRead.ToString());
    }
    Response.AddHeader("Content-Length", ((long)(dataToRead - p)).ToString());
    Response.ContentType = "application/octet-stream";
    Response.AddHeader("Content-Disposition", "attachment; filename=" + System.Web.HttpUtility.UrlEncode(Request.ContentEncoding.GetBytes(filename)));

    iStream.Position = p;
    dataToRead = dataToRead - p;              
    while (dataToRead > 0)
    {                  
        if (Response.IsClientConnected)
        {               
            length = iStream.Read(buffer, 0, 10240);                     
            Response.OutputStream.Write(buffer, 0, length);                      
            Response.Flush();

            buffer = new Byte[10240];
            dataToRead = dataToRead - length;
        }
        else
        {
            //如果用户断开连接 防止无限循环

            dataToRead = -1;
        }
    }
}
catch (Exception ex)
{             
    Response.Write("Error : " + ex.Message);
}
finally
{
    if (iStream != null)
    {
        iStream.Close();
    }
    Response.End();
}
}