Elmah not logging exceptions for http post requests in MVC app - if the request contains XML

Question

I've come across a weird problem in my MVC4 (RC) application. (running on .NET 4.0)

I have just setup Elmah for logging exceptions / errors.

I basically installed the Elmah.MVC and elmah.sqlserver NuGet packages. (versions 2.0.0 and 1.2 respectively)

It seemed to work fine out of the box - I can go to the elmah page and view errors:

http://myserver/elmah

for example, if I create some 404 errors, they appear in this log.

What is not working is this: I have a standard MVC controller with a [HttpPost] action. I've set it up so it will always throw an exception:

public class TestController : Controller
{
    [HttpPost]
    [ValidateInput(false)]
    public void Testing()
    {
        throw new Exception("uh oh");
    }
}

I then try to post data to this controller via jQuery:

$.post('/Test/Testing', {test_data: 'This is some test data'});

Ok, this works. The response returns the typical yellow screen of death, and the error is caught and logged in Elmah.

However, if I try to post something like XML/HTML the error is not logged in Elmah. I still get the same response from the server back (yellow screen of death), but nothing in Elmah.

$.post('/Test/Testing', {test_data: '<test><test1>This is some test data</test1></test>'});

Why? It doesn't make sense.

Notice I have already turned off the request validation on the action. If I didn't do that, then posting XML/HTML data would cause this exception:

A potentially dangerous Request.Form value was detected from the client

NuGet would also refuse to log that exception too - which I believe is a bug:

http://code.google.com/p/elmah/issues/detail?id=217

So what is the cause of this problem that I'm experiencing? It it a bug related to the issue I found above?

It just seems quite an unfortunate situation that I can't log exceptions just because the request contained XML/HTML.

Surely there is a way around this?

Answer 1

ELMAH does not catch HttpRequestValidationException by default and if a user sends an invalid request it will be missed in ELMAH's report. so it's necessary to define and use this global filter as well:

public class ElmahRequestValidationErrorFilter : IExceptionFilter
{
    public void OnException(ExceptionContext context)
    {
        if (context.Exception is HttpRequestValidationException)
           ErrorLog.GetDefault(HttpContext.Current).Log(new Error(context.Exception));
    }
}

Answer 2

I have a work around for now, which someone suggested on http://code.google.com/p/elmah/issues/detail?id=217

You can force ASP to use the older request validation logic by adding this into the <system.web> section of your Web.config:

<httpRuntime requestValidationMode="2.0" />

This will effect the app globally which is not really that great of a situation.

If anyone has something better, please let me know.