ASP.NET MVC Captcha

I was looking for an ASP.NET MVC Captcha control and stumbled upon Nick Berardi’s (http://www.coderjournal.com/2008/06/mvc-captcha-for-preview-release-3/).

First of all I’m using IIS7 and had trouble getting the HttpHandler to register properly.  I ended up with the following steps to get it to work:

1. Add <add verb=”GET” path=”captcha.ashx” validate=”false” type=”ManagedFusion.Web.Handlers.CaptchaImageHandler, ManagedFusion.Web.Captcha” /> to <httpHandlers> in Web.config
2. Add <add name=”CaptchaImageHandler” verb=”GET” path=”captcha.ashx” type=”ManagedFusion.Web.Handlers.CaptchaImageHandler, ManagedFusion.Web.Captcha” /> to the <handlers> section within <system.webserver> in Web.config
3. Add routes.IgnoreRoute(“{handler}.ashx”); to Global.asax

So that got it working, but there were a few pieces of functionality I felt were missing:

1) I wanted the ability to style the CaptchaTextBox

The site I’m working with is pretty design intensive and I needed a way to inject CSS information into the CaptchaTextBox Html Helper.  I reworked the CaptchaHelper and modified the CaptchaTextBox as well as added some overloads:

        public static string CaptchaTextBox(this HtmlHelper helper, string name)
        {
            return helper.CaptchaTextBox(name, null);
        }

        public static string CaptchaTextBox(this HtmlHelper helper, string name, Object htmlAttributes)
        {
            return helper.CaptchaTextBox(name, ((IDictionary<string, object>)new RouteValueDictionary(htmlAttributes)));
        }

        public static string CaptchaTextBox(this HtmlHelper helper, string name, IDictionary<String, Object> htmlAttributes)
        {
            ModelState state;

            TagBuilder builder = new TagBuilder("input");
            builder.MergeAttributes<string, object>(htmlAttributes);
            builder.MergeAttribute("type", "text");
            builder.MergeAttribute("name", name);
            builder.MergeAttribute("id", name);
            builder.MergeAttribute("value", "");
            builder.MergeAttribute("maxlength", ManagedFusion.Web.Controls.CaptchaImage.TextLength.ToString());
            builder.MergeAttribute("autocomplete", "off");

            if (helper.ViewData.ModelState.TryGetValue(name, out state) && (state.Errors.Count > 0))
            {
                builder.AddCssClass("input-validation-error");
            }

            return builder.ToString(TagRenderMode.SelfClosing);
        }

I got the TagBuilder idea from checking out the Reflector on System.Web.MVC.  Pretty cool stuff there.  So now I can use the CaptchaTextBox like so:

<%= Html.CaptchaTextBox(“captcha”, new { @class = “field” })%>

2) I wanted the CaptchaValidationAttribute to invalidate my Model if the captcha isn’t valid

(instead of inject a captchaValid with a value of false into my routedata which is what it does off the shelf)

For this I modified the CaptchaValidationAttribute class.  The first thing I did was make add an ErrorMessage string property.  Then I modified the OnActionExecutingContext method to look like this:

        public override void OnActionExecuting(ActionExecutingContext filterContext)
        {
            // get the guid from the post back
            string guid = filterContext.HttpContext.Request.Form["captcha-guid"];

            // check for the guid because it is required from the rest of the opperation
            if (String.IsNullOrEmpty(guid))
            {
                filterContext.Controller.ViewData.ModelState.AddModelError(Field, ErrorMessage);
                return;
            }

            // get values
            CaptchaImage image = CaptchaImage.GetCachedCaptcha(guid);
            string actualValue = filterContext.HttpContext.Request.Form[Field];
            string expectedValue = image == null ? String.Empty : image.Text;

            // removes the captch from cache so it cannot be used again
            filterContext.HttpContext.Cache.Remove(guid);

            // validate the captch
            if (String.IsNullOrEmpty(actualValue) || String.IsNullOrEmpty(expectedValue) || !String.Equals(actualValue, expectedValue, StringComparison.OrdinalIgnoreCase))
            {
                filterContext.Controller.ViewData.ModelState.AddModelError(Field, ErrorMessage);
                return;
            }
        }

Now I can use the CaptchaValidationAttribute like this:

[CaptchaValidationAttribute()]
public ActionResult Register(FormCollection form)
        {
// INCREDIBLY OVER-SIMPLIFIED BUT YOU GET THE IDEA
            if (!ViewData.ModelState.IsValid)
            {
                return View();
            }
        }

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