How would I hook into/replace the "end user" YSOD?

Question

I want to display the YSOD when it would be providing useful information during development or locally on the servers but a semi-generic page in other cases. I know that I could set the defaultRedirect attribute of the application's <customErrors> configuration tag in web.config, but I would rather do some processing to generate a page with slightly better information.

All of my controllers inherit from one central BaseController class where I have overridden OnException (essentially like this):

protected override void OnException(ExceptionContext filterContext) {
    //if something really bad happened and we get inside this if, 
    //just let the YSOD appear because there isn't anything we can do
    if (filterContext == null)
        return; 

    LogException(filterContext.Exception);

    //insert answer for question here:
    if (FigureOutIfDetailedYsodWouldBeDisplayed(filterContext)) 
        return;

    //what to actually do for end users
    filterContext.ExceptionHandled = true;
    filterContext.Result = View("ErrorPage", GetErrorModel(filterContext));
}

How should I implement FigureOutIfDetailedYsodWouldBeDisplayed (answer need not be code, a pointer in the right direction would be just fine)? My current implementation checks the raw url for the existence of "//localhost", but this solution feels clumsy and doesn't work all the time (for example if the dev has a host entry to type something other than localhost: a requirement our app used to have).

Answer 1

If you actually build using the Debug setting for Dev environments, and Release for production environments, you could always just do

#if DEBUG
    //Show YSOD
#else
    //Show friendly error page
#endif

Answer 2

Did you know you can also add custom error pages per HTTP Error code? Do you really need this custom error handling code then?

  <customErrors mode="RemoteOnly" defaultRedirect="Error/Default">
    <error statusCode="401" redirect="Error/AccessDenied" />
    <error statusCode="404" redirect="Error/NotFound" />
  </customErrors>

Also, unless you have really specific needs, I would recommend not writing this exception logging code yourself. Do yourself a favor and check out ELMAH. Seriously. [disclaimer: I am not involved in this project, just a very happy user]

All it takes is (litterally!) a few lines in your web.config, dropping a dll in your bin folder, and (if you want to log to a DB) a single .sql script.

From the project page:

"ELMAH (Error Logging Modules and Handlers) is an application-wide error logging facility that is completely pluggable. It can be dynamically added to a running ASP.NET web application, or even all ASP.NET web applications on a machine, without any need for re-compilation or re-deployment.

Once ELMAH has been dropped into a running web application and configured appropriately, you get the following facilities without changing a single line of your code:

• Logging of nearly all unhandled exceptions.
• A web page to remotely view the entire log of recoded exceptions.
• A web page to remotely view the full details of any one logged exception.
• In many cases, you can review the original yellow screen of death that ASP.NET generated - for a given exception, even with customErrors mode turned off.
• An e-mail notification of each error at the time it occurs."