London Calling

Ramblings of a software architect in London.

Monthly Archives: February 2009

AnthemNxt HttpModule and other fun and games

I’ve spent most of today doing some more work on AnthemNxt to continue simplifying the code base and making the framework even more fool proof to work with.

  1. Separated out the single project into AnthemNxt.Core and AnthemNxt.Controls. For now development will concentrate on Core and further simplifying that. Any patches for Controls will be happily received however as I know many people have their own Anthem controls kicking about.
  2. Created a dedicated AnthemNxt.Tests web application project which I’ll repopulate with the old Anthem tests at some point, but for now I am using as the basis of my tests for a HttpModule that will simplify Anthem error handling.
  3. Separated script management out of AnthemNxt.Core.Manager into AnthemNxt.Core.ScriptManager with the intention of eventually allowing the use of this ScriptManager in place of the built in ASP.NET one no matter if you are in a callback or not.
  4. Created AnthemSection (configuration section handler for web.config) from where the old settings are now read and where any new settings will be placed.
  5. Created AnthemModule (which is now required to be included in web.config and will be reported as missing if so) which will be used to pave over the slightly manual way in which Anthem used to handle reporting errors back to the browser. The intention is that Application_Error will work identically as it does for postbacks to give you the chance to log information etc, yet redirects to error pages etc from within there will still be honoured using the callback scheme.

I’ve also added two controls of my own:

  • AdvancedValidationSummary (encompasses all the functionality of ValidationSummary but also allows you to place a control that will catch errors for all validation groups that do not have their own summary control)
  • CustomValidator (allows code behind to simply set some text to indicate an error, ideal for logic errors where simple validators are not complex enough).Enough for tonight! Code is committed and builds correctly. :)
  • Error Handling and Exception Logging

    I’ve been struggling with Anthem.NET for some time to work exactly how I would like (and expect) as regards to the event flow for an unhandled page exception.

    In the original 1.5.1 release of Anthem, the Application_Error event was bypassed by a hook added in Manager.OnError as follows:

       1: private void OnError(object source, EventArgs e)
       2: {
       3:     if (IsCallBack)
       4:     {
       5:         _error = HttpContext.Current.Error.ToString();
       6:         HttpContext.Current.ClearError();
       7:         WriteResult(HttpContext.Current.Response, null, _error);
       8:     }
       9: }

    Which meant that any global logging (we use log4net) of an error that you do in Application_Error does not fire and so you end up with the unsatisfactory situation where errors in callbacks occur silently to your operations team whilst returning correct information back to the JS client portion of Anthem.

    This can be worked around by writing a JS Anthem error handler that then calls an AJAX method which triggers a log of a message, but that is convoluted, inefficient and unrelhable and not an acceptable solution for me.

    In the latest source of AnthemNxt I’ve removed the above OnError handler and let the exception proceed as a normal postback would (so my Application_Error handler DOES get hit now and I get exceptions fully logged).

    However now there is a HTML error page returned to the JS client and not a valid JSON response because the OnUnload Anthem handler is never called (since the page rendering is hijacked due to the exception). Until I can write a HttpModule to overcome this and make AnthemNxt a true drop-in library, I’ve broken out the OnUnload AnthemNxt functionality so that it can be called from Application_Error:

       1: private void OnUnload(object sender, EventArgs e)
       2: {
       3:     CompleteRequest();
       4: }
       5:
       6: public void CompleteRequest()
       7: {
       8:     var res = HttpContext.Current.Response;
       9:
      10:     // Handles inserting JS to do a redirect 
      11:     if(Manager.IsCallBack && res.StatusCode == 302)
      12:     {
      13:         string href = res.RedirectLocation.Replace("", "\").Replace("'", "'"); 
      14:         res.RedirectLocation = string.Empty;
      15:         res.Clear();
      16:         res.StatusCode = 200;
      17:
      18:         var sb = new StringBuilder();
      19:         Manager.AddScriptForClientSideEval("window.location='" + href + "';");
      20:         JsonWriter.WriteValueAndError(sb, null, null, null, null, null, null, null, clientSideEvalScripts);
      21:         res.Write(sb.ToString());
      22:         res.End();
      23:     }
      24: }

    as so:

       1: protected void Application_Error(object sender, EventArgs e)
       2: {
       3:     log.Error(ex.Message, ex);
       4:
       5:     // If we are in debug mode get the usual "yellow screen of death" up, makes debugging easier during development 
       6:     if(!Manager.IsCallBack && HttpContext.Current.IsDebuggingEnabled) return;
       7:
       8:     // Redirects to an error page - need to not end the request if this is a callback
       9:     // so that AnthemNxt can write a JS redirect into the JSON response
      10:     Response.Redirect(“~/error.aspx”, !Manager.IsCallBack);
      11:     if(Manager.IsCallBack) Manager.Current.CompleteRequest();
      12: }

    Hopefully with a HttpModule I can make this fully automatic, but for our purposes this is better than the existing behaviour for now :)

    Anyone interested in contributing, whether it be patches, comments or just bugs please get in touch or use the Codeplex project.

    anthem-nxt

    http://www.codeplex.com/anthemnxt

    Well I’ve finally done what I’ve been saying I’d do for quite some time now, forked the Anthem.NET project on sourceforge that has gone pretty stale. I’ve started a new codeplex project for the fork with which my immediate aims are to:

    • Clean up the codebase
    • Incorperate some community and personal bugfixes
    • Drop support for .NET 1.1
    • Make a beta code release

    I’ve already released what I have as a 1.5.2 alpha release so that people just looking for the project can get started easily.

    Longer term I’m looking to:

    • Refactor the JS code so that it works as a jQuery plugin. Will give greater browser compatibility as well as reducing the size of anthem + jQuery overall (as anthem can use jQuery’s AJAX functionality). This will also make the code much more maintainable.
    • Add much more stringent documentation and unit tests.
    • Incorperate some new controls that have common uses.
    • Find ways to allow easy use of jQuery effects with anthem callbacks

    Please let me know what you think. I could do with all the help I can! :)