MSDN Magazine - January 2008 - (Page 60)

Figure 10 Determining the Correct Cache Variation public void OnPostAuthorizeRequest(Object source, EventArgs e) { HttpApplication app = (HttpApplication)source; HttpContext context = app.Context; // Make sure we only process requests to QDIG’s index.php. String requestPath = context.Request.Path; if (!requestPath.Equals(VirtualPathUtility.ToAbsolute (“~/index.php”))) return; // Set up the vary by querystring information HttpCacheVaryByParams varyByParams = context.Response.Cache.VaryByParams; varyByParams[“Qwd”] = true; // gallery path varyByParams[“Qif”] = true; // image to display varyByParams[“Qiv”] = true; // navigation mode varyByParams[“Qis”] = true; // image size varyByParams[“Qtmp”] = true;// other control information // if user is set, also vary by user (See global.asax) context.Response.Cache.SetVaryByCustom(“AuthenticatedUser”); the output cache using the ASP.NET HttpCachePolicy APIs, enabling the output cache module to correctly cache Qdig’s responses: public class QdigOutputCacheModule : IHttpModule { public void Init(HttpApplication application) { application.PostAuthorizeRequest += new EventHandler(OnPostAuthorizeRequest); application.PostRequestHandlerExecute += new EventHandler(OnPostRequestHandlerExecute); } } public void Dispose(){} } Output caching does have a set of limitations, especially when it comes to dynamic content, which often makes deploying a caching solution difficult. The major limitations stem from the dynamic nature of the content. For example, your Web site’s pages may produce different responses based on query-string parameters, time of day, or database updates. If you neglect to take these into account, you may return incorrect cached responses to your users, which will not be a good thing. Fortunately, the ASP.NET output cache takes all of these limitations into account and as a result provides a rich platform for deploying output caching solutions for your application. The ASP.NET page parser provides support for the directive, which allows many output caching settings to be configured directly in the ASPX page. In fact, this is how most developers enable output caching for their ASP.NET applications. Since Qdig is written in PHP, it can’t take advantage of this feature. So instead I will write another module that dynamically configures Figure 11 Configuring the Response to be Cached public void OnPostRequestHandlerExecute(Object source, EventArgs e) { HttpApplication app = (HttpApplication)source; HttpContext context = app.Context; // Make sure we only process requests to QDIG’s index.php. String requestPath = context.Request.Path; if (!requestPath.Equals(VirtualPathUtility.ToAbsolute (“~/index.php”))) return; // Enable this response to be output cached context.Response.Cache.SetCacheability(HttpCacheability.Public); context.Response.Cache.SetExpires(DateTime.Now + TimeSpan.FromMinutes(5)); // code omitted for clarity // add the dependencies to the response context.Response.AddFileDependency(physicalDirectoryPath); context.Response.AddFileDependency(physicalFileName); This time, this module will subscribe to two pipeline events: PostAuthorizeRequest and PostRequestHandlerExecute. The first, PostAuthorizeRequest, occurs right before the output cache module attempts to look up an existing response for the request and return it without further processing. The PostRequestHandlerExecute event occurs right after the handler (PHP) produces the response and before the output cache module attempts to save the response for subsequent use. In the PostAuthorizeRequest event, I need to tell the output cache module how the Qdig responses vary by querystring parameters, so it can find the right response (see Figure 10). By configuring the cache to vary by the querystring parameters, I am enabling the Qdig gallery to operate correctly by responding to the user input such as changing the navigation mode or clicking the next link to go to the next image. Without this, the first request will end up caching its response and returning it for all subsequent requests to the gallery regardless of which image was requested. Also, I will vary by the authenticated user (see the GetVaryByCustomString implementation further), so that the cache correctly gives each authenticated user his own cached copy. In the PostRequestHandlerExecute event, I need to determine whether the response should be cached and configure the appropriate settings allowing it to be cached (see Figure 11). Note the AddFileDependency calls. In the omitted code, I determine the physical path to the gallery directory and the image, if specified, and add a File Dependency to the response. This uses the CacheDependency mechanism supported by the output cache to monitor these resources for changes and to invalidate the cached response when they are modified. This allows me to keep the response cached for a long time, only invalidating it when the underlying data changes. When someone drops a new image or creates a new subgallery, the cache automatically removes the affected cached responses and any new requests will receive the updated pages. The CacheDependency mechanism is a powerful abstraction, allowing you to create your own CacheDependency implementations that can monitor any kind of underlying data—for example, making a Web service call or checking registry keys. The built-in CacheDependency implementations include support for monitoring files, directories, and SQL Server database tables. Deployment and Testing } I deployed the latest module by dropping its QdigOutputCache.cs source file into the App_Code directory, just like I did before, and registered it in web.config: 60 msdnmagazine IIS 7.0 Extensibility

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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