customErrors vs Custom modules

Question

I've currently got httpErrors setup to deal with 500's here:-

<httpErrors errorMode="Custom" existingResponse="Replace">
        ......
        <remove statusCode="500"/>
        <error statusCode="500" path="/server-error" responseMode="ExecuteURL"/>
</httpErrors>

This works fine, but in the case where iis receives the error I still get the yellow screen of death. An example is when entity framework can not connect to the database and I receive:-

Cannot open database "Test-DB" requested by the login.
The login failed.
Login failed for user 'sa'.

I've setup customErrors to deal with this:-

<customErrors mode="On" defaultRedirect="error.html" redirectMode="ResponseRedirect">
        <error statusCode="500" redirect="error.html" />
</customErrors>

which works as expected as long as there is no modules without preCondition="managedHandler".

I have a few modules which deal with images and css files and are in the same project.

<modules runAllManagedModulesForAllRequests="false">
        <add name="ErrorLog" type="Elmah.ErrorLogModule, Elmah" preCondition="managedHandler" />
        <add name="ErrorFilter" type="Elmah.ErrorFilterModule, Elmah" preCondition="managedHandler" />
        <add name="ImageHandler" type="foo.bar.ProductImageHandlerHttpModule" />
        <add name="CustomCssHandler" type="foo.bar.CustomCssHttpModule" />
        <add name="Glimpse" type="Glimpse.AspNet.HttpModule, Glimpse.AspNet" preCondition="integratedMode" />
</modules>

Comment these out and I get the error.html, keep them in and I get

Runtime Error
Description: An exception occurred while processing your request. Additionally, another exception occurred while executing the custom error page for the first exception. The request has been terminated.

showing that a module from the project is also erroring when trying to show the error.html.

Does anyone know a fix/workaround?

Answer 1

Its a tough situation - your error comes from HttpModule, which is run for every single request - including request to error.html page. One way is to route static files (such as error.html) just via your server - and ignore them on .NET level; this may not be always possible (sometimes handling static files on .NET level is handy). The only other way I can think off is hook in global.asax to error event and handle it yourself (which will ignore the customErrors)

Something like:

public class Global : System.Web.HttpApplication
{
    protected void Application_Error(object sender, EventArgs e)
    {
        // is there an error ?
        var error = Server.GetLastError();
        if (error != null)
        {
            // mark the error as - "i'll handle it myself"
            Server.ClearError();
            // load error.html manually & dump it to response
            var content = File.ReadAllText(Server.MapPath("~/error.html"));
            Context.Response.Write(content);
            // set correct error code
            Context.Response.StatusCode = 500;
        }
    }
}

Note: this can be ironed out, but you see the general principle ...