Manual File Downloads In ASP.NET

Another solution explained in this MSKB article is to use the HttpApplication.CompleteRequest method, instead of the Response.End method. Unfortunately, it doesn't help either - the "default" ASP.NET HTML code is still appended to the end of the dynamically generated content even if you call the CompleteRequest method.

Yet another solution that I came acrross on my quest was to completely remove all the HTML code off of the 'download' page (see the post at the end). Although it might work (I haven't tried), I don't like the solution because it feels like a hack (I mean, it is completely undocumented). There is no guarantee that future ASP.NET versions won't put some HTML content to the response buffers even if the associated aspx page is empty.

Again, if you don't feel like mine, the empty aspx page approach is very simple - just open your aspx page in the designer, click the HTML tab and delete all the content except the <@page> directive. If it breaks in the future, please don't blame me - I've warned you. At this point, I finally realized that what I really need is to have complete control over the content sent to the browser - IHttpHandler comes to save the day.

IHttpHandler is an interface defined by ASP.NET, which "Defines the contract that ASP.NET implements to synchronously process HTTP Web requests using custom HTTP handlers. Because I didn't want to change the Download's class name (the Shared CreateHyperlink method was referenced in several other places in the project), I've decided to "morph" the existing Download.aspx web page into a custom IHttpHandler:

I've excluded the Download.aspx file from the project and added a new Download class hosted in an ordinary Download.vb code file. I've added the Implements IHttpHandler clause and implemented the core IHttpHandler.ProcessRequest method by pasting the relevant code from the "old" Download.aspx.vb code-behind file.

In order to actually associate the Download.aspx URL with our custom HTTP handler, the following lines had to be added to the <system.web> section of the application's web.config file:

<httpHandlers>
<add verb="*" path="Download.aspx"
    type="NRozprava.Download, NRozprava"/>
</httpHandlers>

Now, whenever a browser requests the Download.aspx URL, the ASP.NET plumbing instantiates our Download class and calls the IHttpHandler.ProcessRequest method. What is written by the method implementation to the response buffer, exactly that is sent back to the browser - nothing more, nothing less!

The conclusion is simple: If you need to generate custom HTTP responses in your ASP.NET application, use the IHttpHandler-based technique. Forget about the other tricks; they're crude and simply not "politically correct".