AJAX Partial Rendering issues for the default page in IIS 7 when using custom http module

The problem

When I try to make a AJAX partial update request (using the UpdatePanel control) from the default page of an IIS7 web site, it fails- instead of returning the html to be updated, it returns the entire page, which then causes the MS AJAX Javascript to throw a p开发者_如何学运维arsing shit-fit.

The suspected cause

I have narrowed the cause down to two issues- making an AJAX request to the default page when I have a certain custom http module registered. A partial rendering request to http://localhost will fail, but a partial rendering request to http://localhost/default.aspx will work fine. Also, If i remove the following line in my custom HttpModule:

_application.PreRequestHandlerExecute += OnPreRequestHandlerExecute;

The AJAX partial render will work correctly. Wierd huh?

Another wierd thing... If I look at trace.axd, I can see that when a partial rendering request fails, two POST requests are logged for the one partial rendering request- one where the default.aspx page executes successfully (trace information such as page_load is logged) but no content is produced and a second that doesn't seem to actually execute (no trace information is logged) but produces content (HTTP_CONTENT_LENGTH is greater than 0).

Please help! If anyone with a good knowledge of HTTP modules or the MS AJAX Http module could explain why this is occuring I would be very grateful. As it is, the obvious work arround is to just redirect to default.aspx if the request url is "/" but I would really like to understand why this is occurring.

First of all PreRequestHandlerExecute is exactly before HTTP handler executes.

Second for hosting websites with HttpModules under IIS7 it is better that we run website in integrated pipeline mode, and also we have to move HttpModules tag in web.config to system.webServer module section.

If for example you change the handler in PreRequestHandlerExecute like this:

void context_PreRequestHandlerExecute(object sender, EventArgs e)
{
    HttpApplication application = (HttpApplication)sender;
    HttpContext context = application.Context;

    if(  something-happened  )
         context.Handler = null;
}

The result would be exactly as you said.

Setting handler to any thing else but its default, means that ASP.Net is not responsible for current request.

Note that each request only can have one HttpHandler.