C#

int bufferLength = 2048;

Response.ContentType = "application/octet-stream";

Response.AddHeader("Content-Disposition", "attachment; filename=" + Request["document"]);

Response.AddHeader("Content-length", bytes.Length.ToString());

for (int i = 0; i < bytes.Length; i += bufferLength)
{
    // Verify that the client is connected.
    if (Response.IsClientConnected)
    {
        // Write the data to the current output stream.
        if (i + bufferLength < bytes.Length)
            Response.OutputStream.Write(bytes, i, bufferLength);
        else
            Response.OutputStream.Write(bytes, i, bytes.Length - i);

        // Flush the data to the HTML output.
        Response.Flush();
    }
    else
    {
        //prevent infinite loop if user disconnects
        break;
    }
}

Response.Close();

HttpWebRequest request = (HttpWebRequest)WebRequest.Create("");

 request.Accept = "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8";

 HttpWebResponse webResponse = (HttpWebResponse)request.GetResponse();
 response = webResponse.GetResponseStream();

 bytes =  new byte[Convert.ToInt32(webResponse.Headers["Content-length"])];


 for (int i = 0; i < bytes.Length; i += AppContext.BufferLength)
 {
         try
         {

             if (i + AppContext.BufferLength > bytes.Length)
                 response.Read(bytes, i, bytes.Length - i);
             else
                 response.Read(bytes, i, AppContext.BufferLength);
             if (i + AppContext.BufferLength > bytes.Length)
                 control.ReportProgress(i + AppContext.BufferLength, bytes.Length - i);
             else
                 control.ReportProgress(i + AppContext.BufferLength, bytes.Length);

         }
         catch (Exception ex) //-
         {
             exception = ex.Message;
         }

 }

 response.Close();