private void OnSendCompleted(AsyncResult res)
        {
            var stream = this.NetworkStream;

            /*var buff = new byte[4096];
            var bytes = 0;
            do
            {
                bytes += stream.Read(buff, bytes, buff.Length - bytes);
            } while (bytes < buff.Length);
            File.WriteAllBytes("c:\\response.dat", buff);*/

            var httpStateLine = ReadLine(stream);
            var stateMatch = Regex.Match(httpStateLine, @"^HTTP/\d\.\d (?<code>\d+) .+$");
            var stateCode = (HttpStatusCode)int.Parse(stateMatch.Groups["code"].Value);
            var respMsg = new HttpMessage.Response(stream, stateCode);
            string hdr;
            while (!string.IsNullOrEmpty(hdr = ReadLine(stream)))
            {
                var delimiterPos = hdr.IndexOf(": ");
                respMsg.Headers.Add(hdr.Substring(0, delimiterPos), hdr.Substring(delimiterPos + 1));
            }
            switch (stateCode)
            {
                case HttpStatusCode.Continue:
                    // continue reading response
                    this.OnSendCompleted(res); // read next http response
                    break;
                case HttpStatusCode.Found:
                    // temporary redirect
                    res.Client.Close();
                    stream.Dispose();
                    var newUrl = respMsg.Headers["Location"];
                    if (res.RequestMessage.Stream != null)
                    {
                        // need to send data again, move stream to the beginning
                        res.RequestMessage.Stream.Position = res.RequestStreamStart;
                    }
                    this.BeginSend(newUrl, res.RequestMessage, res.CallBack, res.AsyncState);
                    break;
                case HttpStatusCode.OK:
                case HttpStatusCode.PartialContent:
                    var cook = respMsg.Headers["Set-Cookie"];
                    if (this.CookieContainer != null && !string.IsNullOrEmpty(cook))
                    {
                        this.CookieContainer.SetCookies(res.Uri, cook);
                    }
                    res.OnComplete(respMsg);
                    break;
                default:
                    res.ThrowException(new ApplicationException("Server returned: HTTP " + stateCode));
                    break;
            }
        }