Creating an asynchronous HTTP module

ASP.NET 4.5 provides us with the full C# language features described previously in Chapter 2, Exploring the Top New Features of the CLR. Also, the additional methods and features make it easier for us to work with asynchronous language features.

This helps enormously in writing asynchronous HTTP modules and handlers.

Performance is also improved, as the model is asynchronous; it doesn't keep the thread blocked until the request is completed.

Getting ready

In order to use this recipe you should have Visual Studio 2012.

How to do it...

We are going to create an asynchronous HTTP module. An HTTP module allows us to intercept HTTP requests for modifying those requests so we can generate a response in a customized way.

  1. Create a new class library project and name it AsyncHTTPModule.
  2. Add a reference to the System.Web assembly.
  3. Add a class and name it CustomModule. Note that we could as well add an item of type ASP.NET, which would do most of the following for us:
    • Add a Using clause to the System.Web page
    • Make the class implement IHttpModule
    • Right-click on the interface and click on the Implement interface option
    • Add the following asynchronous method:
      private async Task getWebPageContent(object caller, EventArgs e)
{
WebClient wc = new WebClient();
var result = await wc.DownloadStringTaskAsync("http://www.packtpub.com/");

HttpApplication app = (HttpApplication)caller;
app.Response.Write(result);
}
  4. Note that we will need to add a Using clause to System.Net to use the WebClient method.
  5. Next we will implement the Init method:
    public void Init(HttpApplication context)
{
    // We use the EventHandlerTaskAsyncHelper to wrap the task based method to use with the "old" async programming model.
EventHandlerTaskAsyncHelper asyncHelper = new EventHandlerTaskAsyncHelper(getWebPageContent);

    // The helper class instance generates the Begin/End methods for us from a Task Function.
context.AddOnPostAuthorizeRequestAsync(asyncHelper.BeginEventHandler, asyncHelper.EndEventHandler); 
}
  6. We should now implement the dispose method. Leaving it empty will do for now.
  7. And we have our ASP.NET 4.5 asynchronous module ready.

How it works...

In this scenario, the request thread is released when the request has been initiated and a new thread is created when the request finishes, with the response being received on a brand new thread.

Implementing an asynchronous HTTP module fits in perfectly with the core of this behavior.

We implemented IHttpModule and created an asynchronous task. This method can be awaited, which means that it will not block the thread on which it is executed; when it has finished, it will continue from the point where it was awaited, control being returned to the caller of the async method. When an async method or the task it returns finishes, it invokes its continuation from where it left off.

After defining the asynchronous method, which will download the www.packtpub.com website asynchronously and return it as the response, we need to assign it so it can be used by the HTTP module.

We do this with the EventHandlerTaskAsyncHelper class, which we get from the System.Web namespace.

This helper method is meant to integrate a task-based method with the programming model exposed by the ASP.NET HTTP pipeline, which will assign the Begin and End methods to the async helper's BeginEventHandler and EndEventHandler event handlers.

There's more...

It would be interesting to explore the asynchronous HTTP handler feature of ASP.NET 4.5 since the new async features would allow us to significantly improve the performance of our applications.

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