Determine whether or not ELMAH is enabled?

Question

How can I determine programmatically whether or not ELMAH is enabled?

Answer 1

Because:

ELMAH 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.

you should not need to detect whether it is present. Just write your logging code as if it was present, and if it's not, nothing will be logged.

Of interest?: How to get ELMAH to work with ASP.NET MVC [HandleError] attribute? (accepted answer is by ELMAH's author)

Answer 2

You can enumerate all loaded modules (via HttpApplication.Modules) and if Elmah module exists, then Elmah is enabled:

foreach (var m in Application.Modules) {
  if (m is Elmah.ErrorlogModule) {
   // ...
  }
}

Not sure. Haven't treed this.

Answer 3

Further to Tadas' answer, I came up with the following code that works for me (note that I have translated this from VB without checking if it compiles, so YMMV):

bool foundElmah = false;

foreach (var m in HttpContext.Current.ApplicationInstance.Modules) {
    var module = HttpContext.Current.ApplicationInstance.Modules.Item(m);
    if (module is Elmah.ErrorLogModule || module is Elmah.ErrorMailModule || module is Elmah.ErrorFilterModule || module is Elmah.ErrorTweetModule) {
        foundElmah = true;
        break;
    }
}

if (foundElmah) {
    // do something here, like populate the application cache so you don't have to run this code every time
    return true;
} else {
    // store in application cache, etc.
    return false;
}

This also gets around the problems I had with getting a 401 response when requesting elmah.axd (I was using Windows Authentication), and is much faster, and doesn't assume a specific location for elmah.axd.