C# 断点续传

System.IO.Stream iStream  =   null ;

             //  Buffer to read 10K bytes in chunk:
             byte [] buffer  =   new  Byte[ 10240 ];

             //  Length of the file:
             int  length;

             //  Total bytes to read:
             long  dataToRead;

             //  Identify the file to download including its path.
             string  filepath   =   @" E:/software/SQL Server 2000 Personal Edition.ISO " ;

             //  Identify the file name.
             string   filename   =  System.IO.Path.GetFileName(filepath);

             try
             {
                // Open the file.
                iStream = new System.IO.FileStream(filepath, System.IO.FileMode.Open, 
                    System.IO.FileAccess.Read,System.IO.FileShare.Read);
                Response.Clear();

                // Total bytes to read:
                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;
                // Read the bytes.
                while (dataToRead > 0)
                {
                    // Verify that the client is connected.
                    if (Response.IsClientConnected) 
                    {
                        // Read the data in buffer.
                        length = iStream.Read(buffer, 0, 10240);

                        // Write the data to the current output stream.
                        Response.OutputStream.Write(buffer, 0, length);

                        // Flush the data to the HTML output.
                        Response.Flush();

                        buffer= new Byte[10240];
                        dataToRead = dataToRead - length;
                    }
                    else
                    {
                        //prevent infinite loop if user disconnects
                        dataToRead = -1;
                    }
                }
            }
             catch  (Exception ex) 
             {
                // Trap the error, if any.
                Response.Write("Error : " + ex.Message);
            }
             finally
             {
                if (iStream != null) 
                {
                    //Close the file.
                    iStream.Close();
                }
                   Response.End();
            }