MSDN Magazine - January 2008 - (Page 58)

Figure 6 Rewriting URLs public void OnBeginRequest(Object source, EventArgs e) { HttpApplication app = (HttpApplication)source; HttpContext context = app.Context; // Extract the gallery path and image filename from the url // code omitted for clarity // Build the rewritten url String rewrittenUrl = String.Format(“~/index.php?Qwd=.{0}&Qif={1}”, galleryPath, imageFileName); String originalQueryString = context.Request.ServerVariables[“QUERY_STRING”]; if (!String.IsNullOrEmpty(originalQueryString)) { rewrittenUrl += “&” + originalQueryString; } // Rewrite the url context.Server.TransferRequest(rewrittenUrl); rewrite. You can, of course, modify the rewriting scheme in a way that suits your needs. Generating Friendly Hyperlinks Unfortunately, I’m not quite finished. While galleries can now be accessed with friendly URLs, the gallery pages themselves still contain hyperlinks in the old format: } Figure 7 Generating Friendly Hyperlinks public class QdigSEFFilterModule : IHttpModule { public void Init(HttpApplication application) { application.PreRequestHandlerExecute += new EventHandler( OnPreRequestHandlerExecute); } public void Dispose(){} public void OnPreRequestHandlerExecute(Object source, EventArgs e) { HttpApplication app = (HttpApplication)source; HttpContext context = app.Context; if (context.Request.Path.Equals( VirtualPathUtility.ToAbsolute(“~/index.php”))) { // wire up the response filter context.Response.Filter = new QdigSEFFilter(context); } } } ules such as forms authentication are already registered by default. Building on the web.config file created for access control, I can add the new module like so: At this point, you can begin accessing the Qdig gallery using friendly URLs instead of the Qdig native querystring URLs. Now, to access the Flower.jpg file in the Mike subdirectory of the gallery, I can simply request the file like this: http://myphpgallery/Mike/Flower.jpg/show Notice that I chose to use the /show suffix for friendly URLs to differentiate them from direct links to the image files and to prevent my module from rewriting URLs that it is not intended to 58 msdnmagazine IIS 7.0 Extensibility A user clicking on these links will still see the unsightly querystring URLs, and a search engine indexing the content will not be able to correlate the friendly URLs for the parent page with the links in the page body. It would be really handy to make Qdig generate hyperlinks using the same friendly URLs that I enabled in the previous step. But doing this would entail rewriting the PHP script to generate different hyperlinks, which is something I didn’t want to do. It turns out that I don’t have to, thanks to the ASP.NET response filtering facility. I can write another managed module that filters the Qdig responses on the fly, replacing the hyperlinks in the old format with links in the new, friendly format. This time, my module will do the following: 1. Subscribe to the PreRequestHandlerExecute stage of request processing (just before the handler executes). 2. Check whether the URL is for the Qdig index.php script. 3. Set the response filter stream on the response, which will use regular expressions to replace all occurrences of friendly hyperlinks. The module class is pretty simple, since all it does is selectively wire up the filter stream (see Figure 7). The real work is done in the QdigSEFFilter class, which is responsible for replacing all occurrences of Qdig hyperlinks with hyperlinks using the new format. The filter class implements the abstract System.IO.Stream class and is used by the ASP.NET runtime to filter the response at the end of request processing. The ASP.NET Integrated pipeline engine allows the response filter to operate on any response, even those not generated by ASP.NET, and so can be used to process PHP responses as well as static files and ASP pages as long as the response is buffered. IIS 7.0 buffers all responses by default (up to the configured limits), which allows this mechanism to work. My filter implementation will buffer all of the incoming response bytes pushed through its stream, convert them to a string using the charset of the response, and perform the regular expression replacement of URLs. Then it will re-encode the string into the original charset and push the response data back to the runtime. You can find the full implementation of the module and the response filter in the code download. I will again deploy the module code as a separate source file, QdigSEFFilter.cs, into the App_Code directory, and register the module in the configuration section in the application’s web.config. At this point, the modules section will look like this: <add name=”FormsAuthentication” type=

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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