c# 发送http请求并接收返回数据

var url = "http://xxx.123.123.ashx";
            string str_postdata = JsonConvert.SerializeObject(new
            {
                method = "search",mid = "2113",language = 2052,pageNum = 1,pageSize = 30
            });
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
            request.Method = "POST";
            request.ContentType = "application/json;charset=utf-8";
            request.ContentLength = Encoding.UTF8.GetByteCount(str_postdata);
            string authStr = EncryptionUtil.MD5Encrypt32("abcdefg");
            request.Headers.Add("X","abc");
            request.Headers.Add("Y","def");
            request.Headers.Add("X-Auth-Value",authStr);
            Stream myRequestStream = request.GetRequestStream();
            StreamWriter myStreamWriter = new StreamWriter(myRequestStream,Encoding.GetEncoding("gb2312"));
            myStreamWriter.Write(str_postdata);
            myStreamWriter.Close();

            HttpWebResponse response = (HttpWebResponse)request.GetResponse();
            Stream myResponseStream = response.GetResponseStream();
            StreamReader myStreamReader = new StreamReader(myResponseStream,Encoding.GetEncoding("utf-8"));
            string retString = myStreamReader.ReadToEnd();
            Object bupo = JsonConvert.DeserializeObject<Object>(retString);
            myStreamReader.Close();
            myResponseStream.Close();
            return bupo;