post wp8

//spurce: http://stackoverflow.com/questions/14698879/http-post-for-windows-phone-8

//Our generic success callback accepts a stream - to read whatever got sent back from server
public delegate void RESTSuccessCallback(Stream stream);
//the generic fail callback accepts a string - possible dynamic /hardcoded error/exception message from client side
public delegate void RESTErrorCallback(String reason);

public void post(Uri uri,  Dictionary<String, String> post_params, Dictionary<String, String> extra_headers, RESTSuccessCallback success_callback, RESTErrorCallback error_callback)
{
    HttpWebRequest request = WebRequest.CreateHttp(uri);
    //we could move the content-type into a function argument too.
    request.ContentType = "application/x-www-form-urlencoded";
    request.Method = "POST";

    //this might be helpful for APIs that require setting custom headers...
    if (extra_headers != null)
        foreach (String header in extra_headers.Keys)
            try
            {
                request.Headers[header] = extra_headers[header];
            }
            catch (Exception) { }


    //we first obtain an input stream to which to write the body of the HTTP POST
    request.BeginGetRequestStream((IAsyncResult result) =>
    {
        HttpWebRequest preq = result.AsyncState as HttpWebRequest;
        if (preq != null)
        {
            Stream postStream = preq.EndGetRequestStream(result);

            //allow for dynamic spec of post body
            StringBuilder postParamBuilder = new StringBuilder();
            if (post_params != null)
                foreach (String key in post_params.Keys)
                    postParamBuilder.Append(String.Format("{0}={1}", key, post_params[key]));

            Byte[] byteArray = Encoding.UTF8.GetBytes(postParamBuilder.ToString());

            //guess one could just accept a byte[] [via function argument] for arbitrary data types - images, audio,...
            postStream.Write(byteArray, 0, byteArray.Length);
            postStream.Close();


            //we can then finalize the request...
            preq.BeginGetResponse((IAsyncResult final_result) =>
            {
                HttpWebRequest req = final_result.AsyncState as HttpWebRequest;
                if (req != null)
                {
                    try
                    {
                        //we call the success callback as long as we get a response stream
                        WebResponse response = req.EndGetResponse(final_result);
                        success_callback(response.GetResponseStream());
                    }
                    catch (WebException e)
                    {
                        //otherwise call the error/failure callback
                        error_callback(e.Message);
                        return;
                    }
                }
            }, preq);
        }
    }, request);            
}