Umbraco-CMS/src/Umbraco.Web.Common/Extensions/ControllerActionEndpointConventionBuilderExtensions.cs

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Mvc.Controllers;
using Microsoft.AspNetCore.Mvc.Filters;
using Microsoft.AspNetCore.Routing;
using Umbraco.Cms.Core.Models.PublishedContent;
using Umbraco.Cms.Web.Common.Filters;
using Umbraco.Cms.Web.Common.Routing;

namespace Umbraco.Extensions;

public static class ControllerActionEndpointConventionBuilderExtensions
{
    /// <summary>
    ///     Allows for defining a callback to set the returned <see cref="IPublishedContent" /> for the current request for
    ///     this route
    /// </summary>
    public static void ForUmbracoPage(
        this ControllerActionEndpointConventionBuilder builder,
        Func<ActionExecutingContext, IPublishedContent> findContent)
        => builder.Add(convention =>
        {
            // filter out matched endpoints that are suppressed
            if (convention.Metadata.OfType<ISuppressMatchingMetadata>().FirstOrDefault()?.SuppressMatching != true)
            {
                // Get the controller action descriptor
                ControllerActionDescriptor? actionDescriptor =
                    convention.Metadata.OfType<ControllerActionDescriptor>().FirstOrDefault();
                if (actionDescriptor != null)
                {
                    // This is more or less like the IApplicationModelProvider, it allows us to add filters, etc... to the ControllerActionDescriptor
                    // dynamically. Here we will add our custom virtual page filter along with a callback in the endpoint's metadata
                    // to execute in order to find the IPublishedContent for the request.
                    var filter = new UmbracoVirtualPageFilterAttribute();

                    // Check if this already contains this filter since we don't want it applied twice.
                    // This could occur if the controller being routed is IVirtualPageController AND
                    // is being routed with ForUmbracoPage. In that case, ForUmbracoPage wins
                    // because the UmbracoVirtualPageFilterAttribute will check for the metadata first since
                    // that is more explicit and flexible in case the same controller is routed multiple times.
                    if (!actionDescriptor.FilterDescriptors.Any(x => x.Filter is UmbracoVirtualPageFilterAttribute))
                    {
                        actionDescriptor.FilterDescriptors.Add(new FilterDescriptor(filter, 0));
                        convention.Metadata.Add(filter);
                    }

                    convention.Metadata.Add(new CustomRouteContentFinderDelegate(findContent));
                }
            }
        });
}