How to send status code “500” for generic error page in IIS?

Question

I am using a generic error page using ASP.NET's <customErrors> directive.

<customErrors mode="On" defaultRedirect="500.html" redirectMode="ResponseRewrite">
</customErrors>

Problem - when an error occurs, this page does not return HTTP status "500". It comes as 200. So link checkers and spiders do not see that there is any problem.

How can I send the 500 HTTP status along with the static 500.html page?

Requirements:

• I must use redirectMode="ResponseRewrite"
• I can't use a dynamic page, only static .html.

Answer 1

The MSDN documentation for the customErrors element states that it is implemented by System.Web.Configuration.CustomErrorsSection. If we use Red Gate's .NET Reflector to analyze that class, we can see where that setting is used in the Framework.

It is used by System.Web.UI.Page.HandleError and System.Web.HttpResponse.ReportRuntimeError.

Both of these end up calling System.Web.HttpResponse.RedirectToErrorPage. (The name of this method is confusing: it is important to note that RedirectToErrorPage takes the redirectMode setting as a parameter, so it is called even if you are using ResponseRewrite and no redirection actually happens.)

The relevant part of the RedirectToErrorPage method is:

    if (redirectMode == CustomErrorsRedirectMode.ResponseRewrite)
    {
        this.Context.Server.Execute(url);
    }

There doesn't appear to be any way to set the response code in the error handling: at the end of the day it's just a plain Server.Execute. It therefore seems unavoidable that you would need to write code to achieve the HTTP response you want.

Can you re-examine why you want to use a plain .html file? This seems a sensible choice for error handling, because you don't want to go through all the overhead of a .aspx page when that might cause another error to occur.

But perhaps there is some middle ground which will be just as robust as a .html file?

For example, you could make a precompiled HttpHandler, register it to the URL /500.error, and then make 500.error your defaultRedirect page. (This would be similar to how ScriptResource.axd works.) If you precompile your module into a DLL (as opposed to on-the-fly compilation from a plain old .axd file), you may find it is just as robust in the face of error conditions. If you encounter an error where not even this will work, then a static .html file probably won't work either -- keep in mind that the customErrors directive still relies on .NET running under the hood, and still uses the StaticFileHandler to serve your .html file.

Alternatively you could consider a reverse proxy in front of your IIS application which would serve a friendly 500 page even in the face of catastrophic failure of the application pool. This would be more work to set up, but would be even more robust than customErrors, e.g. if your web.config becomes corrupted, even customErrors won't work.

Answer 2

In your gllobal.asax file add the following code

protected void Application_EndRequest(object sender, EventArgs e)
    {
        if (Request.Url.AbsolutePath.EndsWith("500.html"))
            Response.StatusCode = 500;
    }

Answer 3

OK, I have a solution, the only way I can get this to work is by bypassing the custom errors section in the web configuration file.

So, an example default.aspx

public partial class Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        throw new Exception("boom");
    }
}

Then in the global.asax file:

protected void Application_Error(object sender, EventArgs e)
{
    // Clear the error to take control of process
    Server.ClearError();

    Response.WriteFile(Server.MapPath("500.html"));
    Response.StatusCode = 500;
    Response.StatusDescription = "Internal Server Error";
}

You can probably write a better handling mechanism for the 500.html part - I think this should do what you are trying to achieve.

Only tested with VS Cassini web server, however I see no reason why this shouldn't work in iis6.

Answer 4

Try configuring your custom errors section like this:

<customErrors mode="On" redirectMode="ResponseRewrite">
  <error statusCode="500" redirect="500.aspx">
</customErrors>

In your 500.aspx file, change the response code in the page_load;

Response.StatusCode = 500;
Response.StatusDescription = "Internal Server Error";

Answer 5

This could be done with an isapi filter. It would have to be written in c, but it can modify the response status for the .html request so that the browser gets a 500 with you custom html page.

Answer 6

If you insist on changing the core HTTP signaling then you either have to give in on some demands or be prepared to write your own web server. Yes you have to run IIS7 integrated AppPool and you still may have to accept redirection to and active page since you are trying to fake that your server is down and server is not designed to fake suicide. So if it gives you one slim way to do it, your options are to either say thanks or develop your own, non-HTTP compliant server which will scramble response codes at will.