Aspnetcore: Url.Action doesn't respect constraints from IApplicationModelConvention

[BoasE]

Describe the bug

I implemented localized routes using a ApplicationModelConvention.
This works fine as long as I type the urls directly in the browser.

So, for example, german routes are only allowed in german culture. and routes from other languages are returning a 404. Exactly as expected.

But when I use Url.Action it doesn't respect the constraints. so for example if i'm on the english domain i get russian links (depending on the order they are inserted)

What am I doing wrong?

Startup Code:

 services.AddMvc(o =>
            {
                o.Conventions.Insert(0, new LocalizedRouteConvention());
            })

Convention

public class LocalizedRouteConvention : IApplicationModelConvention
{
    public void Apply(ApplicationModel application)
    {
        foreach (var controller in application.Controllers)
        {
            foreach (var action in controller.Actions)
            {
                var attributes = action.Attributes.OfType<RouteAttribute>().ToArray();
                if (!attributes.Any()) return;

                foreach (var attribute in attributes)
                {
                    SelectorModel defaultSelector = action.Selectors.First();

                    foreach (var localizedVersion in GetLocalized(attribute.Template))
                    {
                        if (!action.Selectors.Any(s => s.AttributeRouteModel.Template == localizedVersion.Template))
                        {
                            action.Selectors.Insert(0, new SelectorModel(defaultSelector)
                            {
                                AttributeRouteModel = localizedVersion,
                                ActionConstraints =
                                {
                                    new CultureActionConstraint { Culture = ((LocalizedRouteAttribute) localizedVersion.Attribute).Culture }
                                }
                            });
                        }
                    }
                }
            }
        }
    }
}

And here the constraint

    public class CultureActionConstraint : IActionConstraint
    {
        public string Culture { get; set; }

        public int Order => 0;

        public bool Accept(ActionConstraintContext context)
        {
            return CultureInfo.CurrentCulture.TwoLetterISOLanguageName == Culture;
        }
    }

Expected behavior

Url.Action should also only use the routes that are allowed.

[cypressious]

To reproduce, checkout and run https://github.com/cypressious/asp-net-core-localized-routes-issue, then open http://localhost:5000/about_ru?culture=ru. The generated link should be to http://localhost:5000/privacy_ru but it's actually http://localhost:5000/privacy_bg

When debugging, I noticed that the IActionConstraint is only evaluated when navigating to a URL but not when generating URLs.

[hishamco]

Thanks guys for reproducing the issue, I will try to investigate on this soon

[hishamco]

It takes long time for me to realize that the origin for the issue come from Routing specifically IRouter.GetVirtualPath().

Meanwhile I notice that the router fetches the route template with the first supported cultures sorted by name - I don't know why!! - in your case bg, so that's why the url is privacy_bg, f you add ar culture you will get privacy_ar

@rynowak @JamesNK any ideas what's going on here

[BoasE]

Do you think its a bug or more likely a non specified feature?
Any workaround you can think of? currently this is a showstopper for us.

[hishamco]

I'm not sure why you didn't use RouteDataCultureProvider to simplify the process instead of doing localized routes manually?!!

[BoasE]

@hishamco Sorry i don't understand what exactly you mean. Do you have an example?

[hishamco]

What I mean is you can make of use of Microsoft.AspNetCore.Localization.Routing, have a look to a unit test for more details https://github.com/aspnet/Localization/blob/master/test/Microsoft.AspNetCore.Localization.Routing.Tests/RouteDataRequestCultureProviderTest.cs

[BoasE]

Sorry maybe its a dumb question. But I don't see how i can add localizations of a route this way.

E.g if we have a controller like this

[HttpGet("user")]
public async Task<IActionResult> Get()
{

We have in a storage informations that translates the "user" to "benutzer" in german. and therefore the route should be aviable through /benutzer in french it should be /utilisateur and not "user".

In the Test you provided I can only see how to set and recognize the culture a request shouldhave, but not how to create routes related to the culture.

What am I missing?

[hishamco]

I see you want to create a localized routes, for instance:
http://your-domain.com/user for en culture
http://your-domain.com/benutzer for de culture

[cypressious]

To be precise, we want

http://your-domain.com/user for en culture
http://your-domain.de/benutzer for de culture

[cypressious]

http://your-domain.com/benutzer and
http://your-domain.de/user

should not be allowed

[hishamco]

Seems your implementation is similar to what I saw in this post https://www.strathweb.com/2015/11/localized-routes-with-asp-net-5-and-mvc-6/

[cypressious]

Yes, it's directly inspired by it. However, The author doesn't say anything about GetVirtualPath().

[hishamco]

@filipw did you faced this issue before while you wrote the post that I mentioned above?

[hishamco]

@cypressious @BoasE let me try my last attempt to make workaround to your issue, hope to reply ASAP

[hishamco]

Finally I come up with a simple workaround - perhaps stupid 😄 - to fix your issue

[HtmlTargetElement("a")]
    public class LocalizedLinkTagHelper : TagHelper
    {
        private HttpContext _httpContext;

        public LocalizedLinkTagHelper(IHttpContextAccessor httpContextAccessor)
        {
            _httpContext = httpContextAccessor.HttpContext;
        }

        public override void Process(TagHelperContext context, TagHelperOutput output)
        {
            var selectedCulture = _httpContext.Features.Get<IRequestCultureFeature>().RequestCulture.Culture;
            if (output.Attributes.TryGetAttribute("href", out TagHelperAttribute hrefAttribute))
            {
                var url = hrefAttribute.Value?.ToString();
                var twoLetterISOLanguageName = url?.Split("_")?[1];
                if (twoLetterISOLanguageName != null)
                {
                    url = url.Replace(twoLetterISOLanguageName, selectedCulture.TwoLetterISOLanguageName);
                    output.Attributes.SetAttribute("href", url);
                }
            }
        }
    }

but you should use <a asp-action="Privacy" asp-controller="Home">Privacy</a> instead of @Html.ActionLink("Privacy", "Privacy", "Home"), which confirm that there's a bug here in routing

[BoasE]

As a workaround this should work. But always has the risk that someone uses accidentially method Like Html.Action , Controller.RedirectToAction ...

We will think about the workabout.

In the meanwhile is there a chance to get the behavior in asp core fixed? Should we report it somewhere else?

[hishamco]

As a workaround this should work. But always has the risk that someone uses accidentially method Like Html.Action , Controller.RedirectToAction ...

using asp-controller, asp-action taghelper will work fine in the views, so don't worry about the code, the issue in URL generation

In the meanwhile is there a chance to get the behavior in asp core fixed? Should we report it somewhere else?

IMHO you can move this bug or refer to it in routing repo

[cypressious]

I've created an issue at https://github.com/aspnet/Routing/issues/896

[hishamco]

I'm not sure what's the current status of this?!!

[BoasE]

Well it seems like this is just not implemented and the last comment on the other thread is, that a route constraint should be used, but in the IApplicationModelConvention we don't see a possibilty to add one

[JamesNK]

A route constraint is part of the route. For attribute routing the route constraint would need to be in the template, e.g. the template "{controller}/{action}/{culture:custom-constraint}" would resolve a constraint with the string "custom-constraint". This string is associated with the constraint type in the RouteOptions.

If you want to continue to add new SelectorModel instances then you would add the constraint in a modified template.

I found this blog post that goes into more detail about creating and registering route constraints: https://tommyb.com/blog/customizing-asp-net-cores-route-constraints-and-model-binding/

[mkArtakMSFT]

Thanks for contacting us. We're closing this issue as there was no community involvement here for quite a while now.