如何对 ASP.NET Core 3.1 C# 中的自动“规范链接”重定向器进行重复数据删除？

Question

For every web page within my ASP.NET Core 3.1 C# application, I want to automatically generate an canonical link for SEO purposes.

Currently (POC phase), I have the following snippet in every controller action function:

Uri actualUrl = new Uri($"{HttpContext.Request.Scheme}://{HttpContext.Request.Host}{HttpContext.Request.Path}{HttpContext.Request.QueryString}");
RouteValueDictionary values = RouteData.Values;
values.Remove("controller");
values.Remove("action");
foreach (var q in HttpContext.Request.Query)
    values.Add(q.Key, q.Value);
// Further route/query parameter "fixes" here.
Uri canonicalUrl = new Uri(Url.ActionLink(values: values));
if (!canonicalUrl.Equals(actualUrl))
    return RedirectPermanentPreserveMethod(canonicalUrl.ToString());

This snippet first builds a Uri with the current actual URL. Then it may "fixes" some important route/query parameters (as shown below). Finally it compares the actual uri with the desired uri, and redirects to the desired uri, when the actual uri is different compared to the desired uri (case sensitive).

RouteData.Values["subpage"] = "Digital-Contents";

This process enables the web application to generate the correct canonical url ( http://example.com/MyController/MyAction/Digital-Contents ) for the following sample urls.

• http://example.com/mycontroller/myaction/digital-contents
• http://example.com/Mycontroller/Myaction/Digital-contents
• http://example.com/myconTROLLer/myACTion/digital-Contents

However, the POC is a massive duplication of code, and thus not desirable itself.

My first thought was to use a middleware. However, with an middleware, the action controller cannot "fix" route/query parameters, which are out-of-scope of the regular routing construct (like the "id" route parameter which is shown in most ASP.NET examples). Eg ActionLink is capable of producing the correct case sensitive url slugs for controller and action, but cannot process ("fix") other route/query parameters.

My second thought was to use a generic class, but there I lose the context.

The best solution would be a single (void) function call, which can be placed before the actual action heavy processing (inside the action controller before processing data and generating output).

How to deduplicate this "automatic canonical redirector" code?

Answer 1

This may not be the best solution, i just modified the case based on the code you provided:

 [AttributeUsage(AttributeTargets.Class | AttributeTargets.Method)]
    public class CanonicalUrlAttribute : ActionFilterAttribute
    {
        public override void OnActionExecuting(ActionExecutingContext filterContext)
        {
            var httpContext = filterContext.HttpContext;

            Uri actualUrl = new Uri($"{httpContext.Request.Scheme}://{httpContext.Request.Host}{httpContext.Request.Path}{httpContext.Request.QueryString}");
            RouteValueDictionary values = filterContext.RouteData.Values;
            values.Remove("controller");
            values.Remove("action");
            foreach (var q in httpContext.Request.Query)
                values.Add(q.Key, q.Value);

            // Further route/query parameter "fixes" here.
            Uri canonicalUrl = new Uri(new UrlHelper(filterContext).ActionLink(values));
            if (!canonicalUrl.Equals(actualUrl))
                filterContext.Result = new LocalRedirectResult(canonicalUrl.ToString());
        }
    }

Usage

 [CanonicalUrl]
 public class HomeController : Controller {

}

If you're using names from view models to generate urls like example.com/some-category/some-product then i would use the helper in this Link to generate a slug in kebab case based on the model name (in my case its saved to db on model creation) then with a custom route:

  endpoints.MapControllerRoute(
                    name: "category",
                    pattern: "{Category}/{Product}",
                    defaults: new { controller = "Product", action = "Index" });

This pattern omits the action and controller names from route (which i prefer) and gives you something like this example.com/some-category/some-product and in your action you just compare the model's slug with the route segment that is provided by the user (using the route contraint) like this:

 public async Task<IActionResult> Index([FromRoute,Required] Category,[FromRoute,Required] Product)

and you do a route redirect on mismatch like this:

  return RedirectToRoutePermanent("category", new { Product = Product.Slug, Category = Product.Category.Slug });

Hope this helps.