mvc with webapi

Question

public static string DoWebreqeust(string url, string json)
{
try
{
HttpWebRequest request = (HttpWebRequest)
WebRequest.Create(url); request.KeepAlive = false;
request.ProtocolVersion = HttpVersion.Version10;
request.Method = "POST";
byte[] postBytes = Encoding.UTF8.GetBytes(json);
request.ContentType = "application/json; charset=UTF-8";
request.Accept = "application/json";
// request.ContentType = "application/x-www-form-urlencoded";
request.ContentLength = postBytes.Length;
Stream requestStream = request.GetRequestStream();//error line
requestStream.Write(postBytes, 0, postBytes.Length);
requestStream.Close();
HttpWebResponse response = (HttpWebResponse)request.GetResponse();
string result;
using (StreamReader rdr = new StreamReader(response.GetResponseStream()))
{
result = rdr.ReadToEnd();
}
return result;
}
catch (Exception ex)
{
return "";
}
}

above code 

 

i send a 3 pdf files with base64 data to api

 

'responseStream.Length' threw an exception of type 'System.NotSupportedException'.

Length = 'dataStream.Length' threw an exception of type 'System.NotSupportedException'

Position = 'dataStream.Position' threw an exception of type 'System.NotSupportedException'