How to override web.config customErrors settings at runtime?

Question

I have the following code in the web.config file for my ASP.NET C# app that's hosed on Azure:

<!-- Turn on Custom Errors -->
<!-- Switch the mode to RemoteOnly for Retail/Production -->
<!-- Switch the mode to On for to see error pages in the IDE during development -->
<customErrors mode="On" defaultRedirect="ErrorPage.aspx">
   <error statusCode="403" redirect="ErrorPage403.aspx"/>
   <error statusCode="404" redirect="ErrorPage404.aspx"/>
</customErrors>

This works great for errors when I'm hitting my site site natively (http://ipredikt.com/ErrorPage.aspx), but I also have a Facebook version of the app in which all of the pages use a different MasterPage and hence a different URL (http://ipredikt.com/ErrorPageFB.aspx).

Is it possible to modify the customError redirect values at runtime when I'm running in Facebook app mode, as if I had the following settings in web.config:

<customErrors mode="On" defaultRedirect="ErrorPageFB.aspx">
   <error statusCode="403" redirect="ErrorPage403FB.apx"/>
   <error statusCode="404" redirect="ErrorPage404FB.apx"/>
</customErrors>

I don't think I can set this at the Application scope since it's individual pages in my app that have knowledge of whether they are running in Facebook mode.

kleinohad · Accepted Answer · 2011-06-20 06:20:23Z

1

Hi I think what you can do is make another redirect inside your custom error page acording to the referrer - Request.UrlReferrer sometime the referrer is null so make sure you deal with that

answered Jun 20, 2011 at 6:20

kleinohad

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1 Comment

Armchair Bronco Over a year ago

See comment below about UrlReferrer being null.

Armchair Bronco · Accepted Answer · 2011-06-20 08:40:56Z

1

So here's a brute force solution. I'm using this on the page for the non-Facebook mode 404 errors:

  protected override void OnInit(System.EventArgs e)
  {         
     // If the user tries, for example, to navigate to" /fb/foo/bar
     // then the Request.Url.Query will be as follows after the 404 error: ?aspxerrorpath=/fb/foo/bar
     string queryString = Request.RequestContext.HttpContext.Request.Url.Query;

     string[] str = queryString.Split('=');

     if (str.Length > 0)
     {
        string[] str2 = str[1].Split('/');

        if (str2.Length > 1)
        {
           string test = str2[1].ToLowerInvariant();

           if (test == "fb")
           {
              string pathAndQuery = Request.RequestContext.HttpContext.Request.Url.PathAndQuery;
              string absolutePath = Request.RequestContext.HttpContext.Request.Url.AbsolutePath;

              string mungedVirtualPath = pathAndQuery.Replace(absolutePath, "/ErrorPage404FB.aspx");

              Response.Redirect(mungedVirtualPath);
           }
        }
     }

     base.OnInit(e);
  }

Hardly ideal, but it works.

edited Jun 20, 2011 at 8:40

answered Jun 20, 2011 at 8:15

Armchair Bronco

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1 Comment

Armchair Bronco Over a year ago

Change Server.Transfer() to Response.Redirect() since we want the munged URL to be visible. Server.Transfer honors the new URL but displays the original one.

dahlbyk · Accepted Answer · 2011-06-20 09:15:30Z

1

"Facebook mode" seems like something you could track in Session, which would be accessible in ErrorPage.aspx to trigger a transfer to ErrorPageFB.aspx.

Update - you can clean up your brute-force solution quite a bit by using Request.QueryString:

protected override void OnInit(System.EventArgs e)
{         
    // If the user tries, for example, to navigate to" /fb/foo/bar
    // then the Request.Url.Query will be as follows after the 404 error: ?aspxerrorpath=/fb/foo/bar
    var requestedPath = Request.RequestContext.HttpContext.Request.QueryString["aspxerrorPath"];

    if (requestedPath.StartsWith("/fb/", StringComparison.OrdinalIgnoreCase))
    {
        var requestedUrl = Request.RequestContext.HttpContext.Request.Url;
        var pathAndQuery = requestedUrl.PathAndQuery;
        var absolutePath = requestedUrl.AbsolutePath;

        var mungedVirtualPath = pathAndQuery.Replace(absolutePath, "/ErrorPage404FB.aspx");

        Response.Redirect(mungedVirtualPath);
    }

    base.OnInit(e);
}

Does Request.RequestContext.HttpContext.Request actually return a different instance than simply Request?

edited Jun 20, 2011 at 9:15

answered Jun 20, 2011 at 6:17

dahlbyk

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10 Comments

Armchair Bronco Over a year ago

So you're saying I should just let the redirect from web.config occur, and then do another redirect or a server.transfer() from ErrorPage.aspx if I'm in Facebook mode?

Armchair Bronco Over a year ago

Actually, we don't use Session at all in our app. It's turned off, so that's not an option for us.

kleinohad Over a year ago

Hi look at my suggestion below you can check the URL referrer and then decide if you want to do the redirect to a new error page

dahlbyk Over a year ago

So how do you track which master page should be shown across multiple requests?

Armchair Bronco Over a year ago

The requests from the Facebook app will always be of the form: apps.facebook.com/ipredikt/fb... I will have ASP.NET routing in place that will map this request to: defaultfb.aspx. That page, in turn, knows it's a Facebook page, so it sets the appropriate "IsFacebookPage" variables for the all the ASCX controls that build up the UI. As I noted, it's the pages themselves that know if they are Facebook-mode pages, so I can't set this at the Application scope.

|

kleinohad · Accepted Answer · 2011-06-20 07:14:43Z

0

The easy way to do it is using session but if you don't use session on you website you can always use cookie and when the user arrive to the error page examine the cookie and decide if you want to redirect him to a new error page

answered Jun 20, 2011 at 7:14

kleinohad

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2 Comments

Armchair Bronco Over a year ago

Man, this sure seems like a lot of work to display a Facebook specific version of an error page.

Armchair Bronco Over a year ago

UrlReferrer isn't available. It's null. I'm guessing this is because of the setting in web.config. Looks like the only strings that give me a clue are based on: Request.RequestContext.HttpContext.Request.Url. I get back: localhost:3737/ErrorPage404.aspx?aspxerrorpath=/fb/foo/bar So I can look at the value for "aspxerrorpath", split it on "/", and see if element zero is "fb". Then do Server.Transfer if it is.

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