Question

I have a webforms project and I wanted to log all the 404 errors in the Global.asax, so I put this code there:

void Application_Error(object sender, EventArgs e)
{
    var exception = Server.GetLastError();
    var httpException = exception as HttpException;
    if (httpException == null)
    {
        Log.Error(string.Format("Unkown error:", Request.Url.AbsoluteUri), exception);
    }
    else if (httpException.GetHttpCode() == 404)
    {
        Log.Warn(string.Format("RequestError 404: {0}", HttpContext.Current.Request.Url.AbsoluteUri));
    }
    else
    {
        Log.Error(string.Format("RequestError {0}: {2}\r\n{1}", httpException.GetHttpCode(), Server.UrlDecode(Request.Headers.ToString()), HttpContext.Current.Request.Url.AbsoluteUri), httpException);
    }
}

this works fine with all the request with the extension ‘.aspx’. Without it or with another extension the Application_Error is bypassed.

This is my web.config

<customErrors defaultRedirect="/500.aspx" mode="Off">
  <error statusCode="404" redirect="/404.aspx"/>
  <error statusCode="500" redirect="/500.aspx"/>
</customErrors>

Any idea?

Answer 1

An error handler that is defined in the Global.asax file will only catch errors that occur during processing of requests by the ASP.NET runtime. For example, it will catch the error if a user requests an .aspx file that does not occur in your application. However, it does not catch the error if a user requests a nonexistent .htm file. For non-ASP.NET errors, you can create a custom handler in Internet Information Services (IIS). The custom handler will also not be called for server-level errors.

This is extract from http://msdn.microsoft.com/en-us/library/24395wz3(v=vs.100).aspx