HttpWebRequest和HttpWebResponse

public string HttpRequest(string url, string xml)
        {
            string msg = string.Empty;
            byte[] bytes = Encoding.UTF8.GetBytes(xml);

            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
            request.PreAuthenticate = true;
            request.AllowWriteStreamBuffering = true;
            request.SendChunked = true;
            request.ProtocolVersion = HttpVersion.Version11;
            request.UserAgent = "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.2; .NET CLR 1.1.4322; .NET CLR 2.0.50727)";
            request.Method = "POST";
            request.ContentLength = bytes.Length;
            request.ContentType = "text/xml";
            request.Headers.Add("Authorization", "Basic " + Convert.ToBase64String(new ASCIIEncoding().GetBytes("username:password")));

            //身份凭证
            CredentialCache myCredential = new CredentialCache();
            myCredential.Add(new Uri(url), "Basic", new NetworkCredential("username", "password"));
            request.Credentials = myCredential;

            //发送数据
            using (Stream requestStream = request.GetRequestStream())
            {
                requestStream.Write(bytes, 0, bytes.Length);
            }

            //返回响应
            HttpWebResponse response = (HttpWebResponse)request.GetResponse();

            if (response.StatusCode != HttpStatusCode.OK)
            {
                msg = String.Format("POST failed {0}", response.StatusCode);
            }
            else
            {
                Stream responseStream = response.GetResponseStream();
                StreamReader sr = new StreamReader(responseStream,Encoding.GetEncoding("gbk"));
                msg = sr.ReadToEnd();

                sr.Close();
                response.Close();
            } 

            return msg;
        }