MSDN Magazine - January 2008 - (Page 76)

sending application, the length of the content, the host operating system, and much more. Figure 1 shows an HTTP GET message (lines 1-8) and the reply message (lines 9-14) with several common headers. The Accept header in the HTTP GET request indicates which data formats the client would like to receive. As you can see from the long list of values, the client can receive several kinds of data (images, office documents, Silverlight apps, and so on). The response to the HTTP GET contains data whose format is described by the value of the Content-Type header (image/jpeg as shown on line 10). This simple mechanism allows the sending and receiving application to coordinate data formats. Using headers for data format coordination is not as highly expressive as the Web Services Description Language (WSDL) and XML Schema Definition (XSD) grammars of SOAP Web services, but it’s enough for the Web. REST and the Web service is really a way to expose some functionality via a structured messaging scheme. The principles of the Web (HTTP request/response) are actually describing a subset of possible messaging schemes. Practically all platforms, applications, operating systems, and users understand the principles of the Web, so embracing them in your Web service application gives it improved reach and interoperability. It is important to note that the principles of the Web do not cast a shadow on WS-*, since the choice between REST and WS-* is not mutually exclusive. Neither one can address all types of communication requirements, so I urge you to avoid universally applying either to all services you build. For example, REST is not very good at sending messages to an intermediary, while WS-* excels at it. On the other hand, WS-* applications are not very good at interacting with simple clients like browsers, but REST applications shine at this. By looking at some key parts of the HTTP transport, you have also seen some of the important principles that loosely hold the Web together. In 2000, a PhD student named Roy Fielding finished a dissertation that, among other things, codified these principles into an architectural style known as Representational State Transfer (REST). (You can find Roy’s dissertation at ics.uci.edu/~fielding/pubs/ dissertation/top.htm.) HTTP Programming with WCF Books, software conferences, and a seemingly innumerable collection of blogs have discussed the REST architectural style in finegrained detail. It’s not possible to cover all of its facets here, but I think it is safe reduce it to three key points: • Embrace the URI • HTTP GET is special • Content-Type is the data model For the purposes of this article, let’s consider these points the principles of the Web. By baking these principles into your applications, you dramatically increase the interoperability and reach of your application’s functionality. Interoperability and reach are key drivers behind most Web services initiatives. After all, a Web Figure 1 HTTP GET Request and Response 1 2 GET /PictureServices/Feed.svc/picture/Pictures;Bridge.jpg HTTP/1.1 Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, application/x-ms-application, application/vnd.ms-xpsdocument, application/xaml+xml, application/x-ms-xbap, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, application/x-shockwave-flash, application/x-silverlight, */* Accept-Language: en-us UA-CPU: x86 Accept-Encoding: gzip, deflate User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0; SLCC1; .NET CLR 2.0.50727; InfoPath.2; .NET CLR 1.1.4322; .NET CLR 3.5.20706; .NET CLR 3.0.590; MS-RTC LM 8) Host: www.cloudsamples.net Proxy-Connection: Keep-Alive HTTP/1.1 200 OK Content-Type: image/jpeg Server: Microsoft-IIS/7.0 X-Powered-By: ASP.NET Date: Sat, 15 Sep 2007 18:57:11 GMT Content-Length: 106333 3 4 5 6 7 8 9 10 11 12 13 14 Building on the foundation of these Web basics, let’s take a look at using WCF in the .NET Framework 3.5 to build applications that adhere to the principles of the Web. I’ll start by examining some of the new building blocks of the HTTP programming model and progress upwards through the system. If you’re going to “embrace the URI,” you will probably have to get used to building and parsing URIs. When done by hand, this task is error-prone and tedious. However, the new System.UriTemplate and System.UriTemplateMatch types do the heavy lifting of creating and parsing URIs, and are some of the fundamental building blocks for the new HTTP capabilities of WCF. The UriTemplate type is the basic building block for defining the URI holes discussed earlier. The constructor of the UriTemplate type accepts a String that represents the holes in a URI. Once instantiated, a UriTemplate object exposes two instance methods for binding text values to the holes defined at instantiation. These methods return a URI whose holes are populated with values. A UriTemplate object also exposes an instance method named Match for extracting the values of the holes of a System.Uri object. The Match instance method accepts two System.Uri objects. The first Uri is a base address, and the second Uri is candidate for matching. A System.UriTemplateMatch object is returned from the Match method. The UriTemplateMatch object contains a collection of values for the holes defined at UriTemplate instantiation time. The code in Figure 2 illustrates how to use the UriTemplate and UriTemplateMatch types to round-trip a Uri. The result of this code is the following output: http://localhost:2000/Northwind?album=Overdone the name of the artist is Northwind The System.UriTemplate and System.UriTemplateMatch types are missing the usual WCF System.ServiceModel moniker in the namespace. That’s because their functionality is such that you don’t have to use them inside a WCF application. They are quite handy anytime you need to create or parse a URI. Though the UriTemplate and UriTemplateMatch types are quite easy to use, the WCF team wanted to make it even easier to use 76 msdnmagazine WCF Syndication http://ics.uci.edu/~fielding/pubs/dissertation/top.htm http://ics.uci.edu/~fielding/pubs/dissertation/top.htm

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

MSDN Magazine - January 2008 Contents Toolbox CLR Inside Out Data Points Advanced Basics Cutting Edge IIS 7.0 - Enhance Your Apps with the Integrated ASP.NET Pipeline World Ready - Around the World with ASP.NET AJAX Applications WCF Syndication - HTTP Programming with WCF and the .NET Framework 3.5 Wicked Code Foundations Extreme ASP.NET {End Bracket}

MSDN Magazine - January 2008

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