Exception logging HttpModule doesn't catch errors from ASP .NET Page Method

Question

We have an HttpModule that is designed to catch exceptions and log them to the db. It looks something like this:

public class ExceptionLoggingModule : IHttpModule
{
    public void Init(HttpApplication context)
    {
        context.Error += OnError;
    }

    private static void OnError(object sender, EventArgs e)
    {
        try
        {
            var context = (HttpApplication) sender;
            var exception = context.Server.GetLastError();

            if (exception != null)
            {
                // Log exception
            }
        }
        catch(Exception)
        {
        }
    }
}

This works in general, but I've just noticed that the OnError method never fires when an error occurs within Page Methods (i.e. methods in a code behind file marked with the WebMethod attribute).

How come?

Is there something I can do about this, other than reimplementing the exception logging inside the Page Method itself?

I'm experiencing the same problem today.

Jason Evans
– Jason Evans

2012-11-12 17:01:00 +00:00
Commented Nov 12, 2012 at 17:01 — Jason Evans
– Jason Evans, Commented Nov 12, 2012 at 17:01

Jason Evans · Accepted Answer · 2012-11-12 17:13:04Z

2

I found a solution that worked for me here:

http://blogs.microsoft.co.il/blogs/oshvartz/archive/2008/05/17/asp-net-error-handling-using-httpmodule-full-and-partial-post-back-ajax-updatepanel.aspx

Here's the key points of the handler I've written:

public class PathfinderModule : IHttpModule
{
    public void Init(HttpApplication context)
    {
        context.PostMapRequestHandler += this.OnPostMapRequestHandler;
        context.Error += OnError;
    }

    private void OnPostMapRequestHandler(object sender, EventArgs e)
    {
        Page aux = HttpContext.Current.Handler as Page;

        if (aux != null)
        {
            aux.Error += this.OnPageError;
        }
    }

    private static void OnError(object sender, EventArgs e)
    {
        // Blah..
    }

    private void OnPageError(object sender, EventArgs e)
    {
        // Blah...
    }        
}

answered Nov 12, 2012 at 17:13

Jason Evans

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5 Comments

cbp Over a year ago

Hm this doesn't work from me - if I throw an exception from inside a PageMethod, the event handler doesn't fire.

Jason Evans Over a year ago

Part1: Check the basics - web.config contains the right settings and those settings are formatted/spelled correctly (I've been caught out this a few times). Restart IIS/app pool just to be sure. Place a breakpoint inside the Init() method and attach Visual Studio to the w3wp.exe process which is hosting your site. You want to know that the code is executing

Jason Evans Over a year ago

Part 2: If the attch method doesn't work, then put some Trace.WriteLine() calls in the code so that you can see if that code is being called. Use a tool like DebugOutput from Sysinternals to pick up the WriteLine calls. If your code is not executing at all, then I'm not sure what it could be, sorry.

cbp Over a year ago

Hi thanks, with all the necessary breakpoints I can see it is executing when exceptions are raised during the normal Page lifecycle, but not when raised by PageMethods.

Jason Evans Over a year ago

OK, it might be worth you opening a new question, with a reference to this question, and post the code you are using. Sounds like you may have a different issue then what I suffered. Will make it easier to help you if you discuss it in its own question.

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