PageLoad multiple calls

PageLoad was getting called multiple times for a user control in my Master Page. This had me puzzled for a couple of hours while I was looking in the wrong place for the cause. Then I realised what was going on.

IIS URL rewrite module

The site has a news directory that contains news articles, some static content others dynamic. The master page control in question listed the last few news articles and showed a thumbnail of those articles.

You may start to guess what is coming if I say there was also an IIS url rewriting rule to redirect any request that was not found as a physical file to /news/ and thus return the main news page (default.aspx). This had the effect of redirecting users who were using old links to the new front page.

Missing images

What happened was that development machine had got out of sync with the thumbnail images for this control. Thus when the browser asked for the missing thumbnail, instead IIS did a redirect for that request to /news/. In effect calling the default.aspx for the news directory. As the news front page was sent to the browser instead of the image, the header was rendered as part of this request for default.aspx, resulting in the page header control getting multiple hits depending on how many broken images were present.

This was identified as soon as fiddler was used to look at what the browser was up to. At this point all became very easy to see, several 200 requests for the /news/ url.

The solution for me was to limit the redirect in IIS to be just for .html/.aspx/.htm/.js etc. This solved the problem and properly reported missing images as not found.

Empty image tags

I also noticed a few people talking about empty image tags in server controls causing this same issue. They are correct, even without IIS redirects, there is a redirect in operation, that of serving default.aspx when an empty directory is called. If you have any image tags that render to an empty tag, the browser will unwittingly request default.aspx for the image. This will fire your page events twice or more depending on how many of these links lie in the page. I didn’t see any explanations for this behaviour in those posts so cover it here in case this variation on my issue catches you out.

Custom error pages replaced by IIS?

Development Machine W7, Production IIS7 Windows 2008

Just had a sticky problem crop up in production. Custom error pages that used to work no longer work, I don’t know when but sometime our custom ASP.NET error pages have been replaced by stock IIS error pages.

How we use custom error pages

If a website user or search bot attempts to access a product page and the product no longer exists, we send them to a custom error page. The page suggests they try another product or search for alternatives. This page sends back a http 404 status so that the search engines know to drop the accessed URL from the index. It also causes our Google Mini to drop the page from its database too. If the user navigates to another url that has never had content they get a default 404 page returned.

Lets have a look

So you have a great little custom error page like this;

Protected Sub Page_Load1(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

        'Ensure a 404 not found sent for SEO purposes

        Response.StatusCode = 404

        Response.TrySkipIisCustomErrors = True

    End Sub

However even browsing direct to the page you only get,

This is not your crafted custom page, instead this is the IIS7 page kicking in. IIS has put itself in the pipeline to the end user, replacing its own page with in place of the custom page.

IIS custom page configuration

The configuration for this is found in the site Error Pages section;

If you go into this menu you see all the custom error pages set up in IIS, now select the edit feature settings link on the right hand side;

This is where the behaviour is set and currently this is set to show detail errors for users local to the machine but custom errors for people elsewhere. Note this is not ASP.NET, although the idea is the same, this is above ASP.NET, it is the handling IIS does for these pages.

You do not want normal users to see the detailed errors as it can give away important information about the configuration of your server thus the setting shown is fine and looking at it one would guess it would show our custom pages as we saw by the returned IIS 404 page this is not the case.

So why do we not see our custom pages? Well back in the page code behind shot earlier is the key, you must set

Response.TrySkipIisCustomErrors = True

This tells IIS to get its nose out of what we’re up to and let us get on with it. Trying to browse the custom error page, now we get our custom error page retuned as would be expected in the first case.

Lesson learnt

The real nasty bit of this is that our development machines do not exhibit this behaviour, everything looks fine there. As Rick Strahl says it is another good case for using the staging servers with the production environment so that you test everything.

Other links:

Rick Strahl's Web Log has an almost identical post here

What to expect from IIS7 custom error modulethis link was the one that taught me what I needed to solve the problem.

I found this problem the other day, debugging a site I set the disable script option on the developer toolbar to check for none JavaScript browser support. Then later I wanted to use other sites as normal but found that all JavaScript was still disabled. Opening the developer tools, the option was greyed out in the developer tools of Internet Explorer thus I was unable to get JavaScript running again in the browser. I asked around the office to find others had seen this but never worked out how to fix it.

I went experimenting, what I discovered was that this option is only available if the current site has trust. Try adding the site into trusted sites or Intranet under I was back in business.

Set the options in Internet Options

You MUST refresh the page for this to take effect.

The script option is available again. This was even though this site was on our intranet. Thus the automatic detection of Intranet sites in our scenario is not adequate.

One of our designers made an error today, placing images they wanted to appear in a directory called “POPUP”. We use the JavaScript library Lightbox to give smooth popup images for products in the website, so popup in that sense was appropriate.

The anti-virus solution we have has advertising blocking in it. This software running on the client machines blocked the functionality of the page. Thus making it useless.

After consulting me as to what the problem was, a lesson was learnt.

Don’t use directories names that sound like spam on your websites!