IHttpHandler vs IHttpModule

Dan_19020 0
Viewed 27176

My question is simple (although the answer will most likely not be): I'm trying to decide how to implement a server side upload handler in C# / ASP.NET.

I've used both HttpModules (IHttpModule interface) and HttpHandlers (IHttpHandler interface) and it occurs to me that I could implement this using either mechanism. It also occurs to me that I don't understand the differences between the two.

So my question is this: In what cases would I choose to use IHttpHandler instead of IHttpModule (and vice/versa)?

Is one executed much higher in the pipeline? Is one much easier to configure in certain situations? Does one not work well with medium security?

httphandler httpmodule iis asp.net c#
5 Answers

As stated here, HttpModules are simple classes that can plug themselves into the request processing pipeline, whereas HttpHandlers differ from HttpModules not only because of their positions in the request processing pipeline, but also because they must be mapped to a specific file extensions.

user_836640

IHttpModule gives you much more control, you can basically control all of the traffic directed to your Web application. IHttpHandler gives you less control (the traffic is filtered before it reaches your handler), but if this is sufficient for your needs, then I see no reason to use the IHttpModule.

Anyway, it's probably best to have your custom logic in a separate class, and then just use this class from either IHttpModule or IHttpHandler. This way you don't really have to worry about choosing one or the other. In fact, you could create an extra class which implements both IHttpHandler and IHttpModule and then decide what to use by setting it in Web.config.

Igor_Brejc_554080

15 seconds has a nice small tutorial giving practical example

YordanGeorgiev_657060

Modules are intended to handle events raised by the application before and after the request is actually processed by the handler. Handlers, on the other hand, aren't given the opportunity to subscribe to any application events and, instead, simply get their ProcessRequest method invoked in order to the "main" work of processing a specific request.

Take a look at this documentation from Microsoft (about half way down the page in the "The request is processed by the HttpApplication pipeline" section):

http://msdn.microsoft.com/en-us/library/bb470252.aspx

You can see in step 15 where the handler gets its chance to execute. All of the events before and after that step are available for interception by modules, but not handlers.

Depending on what specific features you're trying to achieve, you could use either a handler or a module to implement an upload handler. You might even end up using both.

Something to consider might to use an upload handler that's already written.

Here's a free and open source one:

http://www.brettle.com/neatupload

Here's a commercial one:

http://krystalware.com/Products/SlickUpload/

If you look at the documentation for NeatUpload, you'll see that it requires you to configure a module.

user_503900
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