gistfile1.cs

public IObservable<WebResponse> MakeWebRequest(
        Uri uri, 
        Dictionary<string, string> headers = null, 
        string content = null,
        int retries = 3,
        TimeSpan? timeout = null)
{
    var request = Observable.Defer(() =>
    {
        var hwr = WebRequest.Create(uri);
        if (headers != null)
        {
            headers.ForEach(x => hwr.Headers[x.Key] = x.Value);
        }

        if (content == null)
        {
            return Observable.FromAsyncPattern<WebResponse>(hwr.BeginGetResponse, hwr.EndGetResponse)();
        }

        var buf = Encoding.UTF8.GetBytes(content);
        return Observable.FromAsyncPattern<Stream>(hwr.BeginGetRequestStream, hwr.EndGetRequestStream)()
            .SelectMany(x => Observable.FromAsyncPattern<byte[], int, int>(x.BeginWrite, x.EndWrite)(buf, 0, buf.Length))
            .SelectMany(_ => Observable.FromAsyncPattern<WebResponse>(hwr.BeginGetResponse, hwr.EndGetResponse)());
    });

    return request.Timeout(timeout ?? TimeSpan.FromSeconds(15)).Retry(retries);
}