Failing ASP.NET MVC route. Is this a bug or corner case?

Question

I have an ASP.NET MVC 3 application where users can post suggestions along the lines of "bla bla would be better if yada yada yada". For the suggestion detail page I have defined a nice SEO friendly route as follows:

routes.MapRoute(null, "suggestion/{id}/{it}/would-be-better-if-{if}", 
    new { controller = "suggestion", action = "details" });

As you can see I want the "would be better if" part to be fixed.

This route works perfectly for any old suggestion and generates links like suggestion/5/this-site/would-be-better-if-it-had-a-iphone-application, and clicking on the link actually requests the appropriate detail page.

A friend of mine, who ironically happens to be a tester, has managed to, involuntarily, post a suggestion that actually breaks the route: "This site would be better if 'would be better if' was always aligned in the middle".
The link generated for this suggestion is /suggestion/84/this-site/would-be-better-if-would-be-better-if-was-always-alligned-in-the-middle.

I have tried Phil Haack's Routing Debugger and have confirmed that the route will actually work up until suggestion/84/this-site/would-be-better-if-would-be-better-if-, so the second "would-be-better-if" is actually accepted; adding anything after that will actually cause the url not to match any route (thanks to Omar -see comments- for help).

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Please bear in mind that I really don't want to change the route definition since I think it is as good as I can manage for this case, SEO-wise.

So, how come having text equal to the fixed part of the route prevents the link from matching the route? why is the route breaking?

I am actually rahter more interested in the why, as I believe understanding the why will lead to a solution or at least a proper understanding of a rather interesting problem.

Answer 1

This looks like a dupe of ASP.NET routing: Literal sub-segment between tokens, and route values with a character from the literal sub-segment which is a much simpler version of the bug. I'd recommend closing this one in favor of that one.

I answered that question.

Answer 2

I'm not sure why it behaves this way, but you can use something like this:

public interface IRouteRule
{
    object ProcessIncoming(object value);
    object ProcessOutgoing(object value);
}

public class StartsWithRouteRule : IRouteRule
{
    public StartsWithRouteRule(string value)
    {
        Value = value;
    }

    public string Value { get; protected set; }

    public object ProcessIncoming(object value)
    {
        var result = value as string;
        if (result == null)
            return null;

        if (!result.StartsWith(Value))
            return null;

        return result.Substring(Value.Length);
    }

    public object ProcessOutgoing(object value)
    {
        var result = value as string;
        if (result == null)
            return null;

        return Value + result;
    }
}

public class ComplexRoute : Route
{
    public ComplexRoute(string url, object defaults, object rules)
        : this(url, new RouteValueDictionary(defaults), rules)
    { }
    public ComplexRoute(string url, RouteValueDictionary defaults, object rules)
        : base(url, defaults, new MvcRouteHandler())
    {
        Rules = new Dictionary<string, IRouteRule>();
        foreach (var pair in new RouteValueDictionary(rules))
            Rules.Add(pair.Key, (IRouteRule)pair.Value);
    }

    public Dictionary<string, IRouteRule> Rules { get; protected set; }

    public override RouteData GetRouteData(HttpContextBase httpContext)
    {
        var result = base.GetRouteData(httpContext);

        if (result == null)
            return null;

        foreach (var pair in Rules)
        {
            var currentValue = result.Values[pair.Key];
            if (currentValue == null)
                return null;

            var value = pair.Value.ProcessIncoming(currentValue);
            if (value == null)
                return null;

            result.Values[pair.Key] = value;
        }

        return result;
    }

    public override VirtualPathData GetVirtualPath(RequestContext requestContext, RouteValueDictionary values)
    {
        values = new RouteValueDictionary(values);

        foreach (var pair in Rules)
        {
            var currentValue = values[pair.Key];
            if (currentValue == null)
                return null;

            var value = pair.Value.ProcessOutgoing(currentValue);
            if (value == null)
                return null;

            values[pair.Key] = value;
        }

        return base.GetVirtualPath(requestContext, values);
    }
}

Usage:

routes.Add(new ComplexRoute(
    "suggestion/{id}/{it}/{if}",
    new { controller = "suggestion", action = "details" },
    new { @if = new StartsWithRouteRule("would-be-better-if-") }));