missing post data by using HttpWebRequest

Question

I got a problem on posting data by using HttpWebRequest.

There is a string(ie. key1=value1&key2=value2&key3=value3) and I have post it to a site (ie. www.*.com/edit), but ,I don't know why that sometimes it's nothing wrong , but sometimes ,the first key=value1 will be missing, only key2=value&key3=value3 that can find in HttpAnalyzer.

public static string SubmitData(string Url, string FormData, CookieContainer _Cc, string ContentType)
        {
            Stream RequestStream = null, ResponseStream = null; StreamReader Sr = null;
            HttpWebRequest HRequest = (HttpWebRequest)WebRequest.Create(Url);
            try
            {

                HRequest.CookieContainer = _Cc;
                HRequest.Method = "POST";
                HRequest.UserAgent = "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0)";
                HRequest.ContentType = ContentType;
                HRequest.ContentLength = FormData.Length;
                //byte[] BFromData = new ASCIIEncoding().GetBytes(FormData);
                byte[] BFromData = Encoding.ASCII.GetBytes(FormData);
                BFromData = Encoding.Convert(Encoding.ASCII, Encoding.UTF8, BFromData);//ascii → utf8
                RequestStream = HRequest.GetRequestStream();
                RequestStream.Write(BFromData, 0, BFromData.Length);
                //RequestStream.Write(utf8Bytes,0,utf8Bytes.Length );
                HttpWebResponse HResponse = (HttpWebResponse)HRequest.GetResponse();
                ResponseStream = HResponse.GetResponseStream();
                Sr = new StreamReader(ResponseStream, Encoding.UTF8);
                return Sr.ReadToEnd();
            }
            catch
            {
                return "";
            }
            finally
            {
                if (null != RequestStream) RequestStream.Close();
                if (null != ResponseStream) ResponseStream.Close();
                if (null != Sr) Sr.Close();
            }
        }

Answer 1

Use Fiddler to see how the request looks like when you click on the form then try using this approach and modify what you need for your request.

public static void PostDataAndDoSomething()
        {            
            string URI = "http://www.something.com";
            //make your request payload
            string requestBody = String.Format("{{'param1': {0}, 'param2': {1}}}",value1, value2); //json format

            HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(URI);  //make request         

            // set request headers as you need
            request.ContentType = "application/json; charset=UTF-8"; 
            request.Accept = "application/json, text/javascript;
            request.Method = "POST";            
            request.UserAgent = "";
            request.Headers.Add("X-Requested-With", "XMLHttpRequest");
            using (StreamWriter writer = new StreamWriter(request.GetRequestStream()))
            {
                writer.Write(requestBody); //write your request payload
            }

            WebResponse response = request.GetResponse();          
            string jsonData = String.Empty;

            using (var reader = new StreamReader(response.GetResponseStream()))
            {
                jsonData = reader.ReadToEnd();
            }           
            response.Close();

            //do something with your data, deserialize, Regex etc....
        }