Using reactive extensions with WebRequest

I’ve recently started looking at the Rx library from Microsoft labs and it’s very interesting stuff, even though I have to admit I have a hard time wrapping my head around it. But it starts to sink in, bit by bit

When working with Windows Phone 7 development and my SharePoint library for WP7, I do a lot of asynchronous calls to web services. This code can often get a bit messy with all the callback methods so I tried to refactor it using reactive extensions and I am pretty pleased with the result:) I’m no expert on the field so I won’t guarantee that this is the best way to do it, but it works.

Here’s a sample of how to do a call to the Lists.asmx web service in SharePoint:

string Envelope = @"<?xml version=""1.0"" encoding=""utf-8""?>
                                    <soap:Envelope xmlns:xsi=""http://www.w3.org/2001/XMLSchema-instance"" xmlns:xsd=""http://www.w3.org/2001/XMLSchema"" xmlns:soap=""http://schemas.xmlsoap.org/soap/envelope/"">
                                        <soap:Body>
                                            <GetList xmlns=""http://schemas.microsoft.com/sharepoint/soap/"">
                                                <listName>{0}</listName>
                                            </GetList>
                                        </soap:Body>
                                    </soap:Envelope>";

        public void GetList(string server, string name, Action<XDocument> handler)
        {
            HttpWebRequest req = WebRequest.Create(string.Format("{0}/_vti_bin/lists.asmx", server)) as HttpWebRequest;
            req.Headers["SOAPAction"] = "http://schemas.microsoft.com/sharepoint/soap/GetList";
            req.ContentType = "text/xml; charset=utf-8";
            req.Method = "POST";
            var listRequest = (from request in Observable.FromAsyncPattern<Stream>(req.BeginGetRequestStream, req.EndGetRequestStream)().Do(stream =>
            {
                UTF8Encoding encoding = new UTF8Encoding();
                string e = string.Format(Envelope, name);
                byte[] bytes = encoding.GetBytes(e);
                stream.Write(bytes, 0, bytes.Length);
                stream.Close();
            })
                     from response in Observable.FromAsyncPattern<WebResponse>(req.BeginGetResponse, req.EndGetResponse)()
                     select HandleResponse(response)).Subscribe(handler);
        }
        private void DoStuff(XDocument xml)
        {
                //parse the xml result here
        }
        private XDocument HandleResponse(WebResponse response)
        {
            HttpWebResponse res = response as HttpWebResponse;
            if (res != null && res.StatusCode == HttpStatusCode.OK)
            {
                XDocument doc = XDocument.Load(response.GetResponseStream());
                return doc;
            }
            return null;
        }

Then of course we call the method:

GetList("http://spserver.com", "Pages", DoStuff);

In Windows Phone 7 we could add .ObserveOnDispatcher() before our .Subscribe() in the LINQ query so that the current Dispatcher is used when notifying observers.

We could also generalize the method so that it returns a IObservable<T> instead which we can subscribe to.

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