MSDN Magazine - June 2008 - (Page 50)

this contract and URI. In this scenario, the back-end system plays the role of the WCF client and broadcasts (publishes) a message to all subscribers, as illustrated here: static void DoPriceUpdate(PriceUpdate pu) { EndpointAddress ea = new EndpointAddress( "sb://connect.biztalk.net/services/contososervices/priceupdate"); ChannelFactory cf = new ChannelFactory ( new RelayBinding(RelayConnectionMode.RelayedMulticast), ea); IPriceUpdateService service = cf.CreateChannel(); service.UpdatePrice(pu); } Figure 6 Producing a Web Feed public Atom10FeedFormatter GetPriceUpdate() { SyndicationFeed feed = new SyndicationFeed("Product Update Feed", "", null); List items = new List (); feed.Items = items; IEnumerable products = GetUpdatedProducts(); string iText = "Product update for {0}. Old price={1}. New Price={2}"; foreach (var product in products) { items.Add(new SyndicationItem("Product update for " + product.Name, String.Format(iText, product.Name, product.OldUnitPrice, product.UnitPrice), null, product.Name, product.UpdatedTime)); } return new Atom10FeedFormatter(feed); } When UpdatePrice is called, the PriceUpdate message is sent to BizTalk Connectivity Services, which then relays the message to all the services currently subscribed to the same URI. Passing through Firewalls with RelayedHttp RelayedHttp mode enables you to take an HTTP service running on your local network and expose it through BizTalk Connectivity Services via HTTP on the public Web, even if that service would not normally be directly accessible from outside your network. This feature is especially handy when used in conjunction with the new WCF Web programming model found in the .NET Framework 3.5. This new Web programming model makes it easier to implement RESTful Web services with WCF. It also provides features that make it easy to integrate your WCF services with existing RSS/Atom and AJAX infrastructure found on the Web today. BizTalk Services doesn’t require the .NET Framework 3.5, but given these new WCF features, RelayedHttp mode has more functionality when you have the .NET Framework 3.5 installed. Going back to the sales application, sometimes salespeople are not running the rich client application, but they still need to be notified of the latest pricing information. One interesting way to expose data that is updated often is through a Web feed—an HTTP endpoint that returns well-known XML formats, such as RSS or Atom, to applications that know how to consume those feeds. Web feeds can be polled for new content on a set schedule by a feed reader (the common name for a program that aggregates Web feeds into a human-facing UI). This enables the end user to receive updates without actively navigating to the site but rather by looking at his feed reader. Using the WCF Web programming model, we can easily build a Web feed that exposes the price update data. The first thing we need is a contract that uses the new WCF attributes for enabling HTTP invocations. These attributes inform the WCF messaging layer how to route incoming HTTP requests to the methods on the service based on the URI rather than the SOAP Action header. Here’s an example: [ServiceContract] public interface IPriceUpdateFeed { [OperationContract()] [WebGet(UriTemplate = "*")] Atom10FeedFormatter GetPriceUpdate(); } Also note the UriTemplate property on WebGetAttribute. This tells WCF exactly how to route incoming messages to different methods based on the URI of the incoming request. This example uses a wildcard template (“*”) to indicate that we want all GET requests routed to this particular method. You could easily configure multiple methods on a service, each of which handles a different UriTemplate. There’s also a WebInvokeAttribute that you can use when you want to respond to other HTTP verbs besides GET (including POST, PUT, DELETE, and HEAD). The other thing to notice about this contract is the method’s return type. The WCF Web programming model includes new types specifically designed to help produce today’s standard feed formats. The two major formats supported today are Atom and RSS. The example here uses the Atom format. WCF 3.5 comes with a new binding class that makes configuring endpoints easy. Figure 6 shows a simple implementation of the GetPriceUpdate operation that produces an Atom syndication feed. This implementation uses the new SyndicationFeed API for producing a logical feed, which it returns wrapped in an Atom10FeedFormatter object in order to produce the correct XML format. Now we need to configure an endpoint to listen for these requests. WCF 3.5 comes with a new binding class to make configuring the endpoint very easy. The WebHttpBinding class encapsulates the details around creating a RESTful channel stack that won’t expect SOAP messages. It simply uses the HTTP transport and the textbased message encoder from WCF, with the message version of the encoder set to None. Here is the code required to get our new endpoint hooked up and running: ServiceEndpoint se = sh.AddServiceEndpoint(typeof(IPriceUpdateFeed), new WebHttpBinding(), "http://localhost:8099/ProductFeed"); se.Behaviors.Add(new WebHttpBehavior()); Here WebGetAttribute tells WCF that this method should be called whenever an HTTP GET request arrives at the service (in contrast to SOAP requests, which always use HTTP POST). 50 msdn magazine BizTalk Services

Table of Contents Feed for the Digital Edition of MSDN Magazine - June 2008

MSDN Magazine - June 2008 Contents Toolbox CLR Inside Out Cutting Edge Patterns In Practice SAAS Concurrency Robotics Form Filler GUI Library Service Station Foundations Windows With C++ Concurrent Affairs Going Places { End Bracket }

MSDN Magazine - June 2008

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