DBService.GetDataAsync

DBService.cs

// ORIGINAL

private static void GetDataAsync<T, TRequest>(TRequest input, Action<T, TRequest, string> callback)
{
    var request = HttpWebRequest.Create(DBService.ServiceUrl);
    request.Method = "POST";

    request.BeginGetRequestStream(asyncRequest =>
    {
        try
        {
            var httpRequestStream = request.EndGetRequestStream(asyncRequest);

            if (httpRequestStream != null)
            {
                using (var writer = new StreamWriter(httpRequestStream))
                {
                    var obj = JsonConvert.SerializeObject(input);
                    writer.WriteLine(obj);
                }

                request.BeginGetResponse(asyncResponse =>
                {
                    try
                    {
                        var httpResponse = request.EndGetResponse(asyncResponse);
                        var httpResponseStream = httpResponse.GetResponseStream();

                        using (var reader = new StreamReader(httpResponseStream))
                        {
                            var json = reader.ReadToEnd();
                            var result = JsonConvert.DeserializeObject<T>(json);

                            callback(result, input, json);
                        }
                    }
                    catch (WebException e)
                    {
                        System.Diagnostics.Debug.WriteLine(e.Message);
                    }
                }, asyncRequest);
            }
        }
        catch (Exception e)
        {
            System.Diagnostics.Debug.WriteLine(e.Message);
        }
    }, request);
}

// REWRITTEN USING REACTIVE EXTENSIONS

private static IObservable<T> GetDataAsync<T, TRequest>(TRequest input)
{
    var request = HttpWebRequest.Create(DBService.ServiceUrl);
    request.Method = "POST";

    var getRequestStream = Observable.FromAsyncPattern<Stream>(
        request.BeginGetRequestStream, 
        request.EndGetRequestStream);
    
    var getResponse = Observable.FromAsyncPattern<WebResponse>(
        request.BeginGetResponse,
        request.EndGetResponse);

    return getRequestStream()
                .SelectMany(stream => 
                {
                    using (var writer = new StreamWriter(stream))
                        writer.WriteLine(JsonConvert.SerializeObject(input));

                    return getResponse();
                })
                .Select(webResponse =>
                {
                    using (var reader = new StreamReader(webResponse.GetResponseStream()))
                        return JsonConvert.DeserializeObject<T>(reader.ReadToEnd());
                });        
}