dotnet core mvc sitemap generator

SitemapGenerator.cs

// Modified code from http://dotnetthoughts.net/generate-dynamic-xml-sitemaps-in-aspnet5/

public static class SitemapGenerator
{
    private static string _sitemapContent = null;
    public static string Generate(string rootUrl, IUrlHelper urlHelper)
    {
        if (_sitemapContent == null) // I only wanted to generate this once and then stash the result. Caching the action that calls this would probably be better
        {
            string sitemapContent = "<urlset xmlns=\"http://www.sitemaps.org/schemas/sitemap/0.9\">";
            var controllers = Assembly.GetExecutingAssembly().GetTypes().Where(type => typeof(Controller).IsAssignableFrom(type) || type.Name.EndsWith("controller")).ToList();

            foreach (var controller in controllers)
            {
                var methods = controller.GetMethods(BindingFlags.Public | BindingFlags.Instance | BindingFlags.DeclaredOnly)
                                        .Where(method => typeof(IActionResult).IsAssignableFrom(method.ReturnType))
                                        .Where(method => controller.GetCustomAttributes(typeof(IncludeInSitemapAttribute), true).Any() || method.GetCustomAttributes(typeof(IncludeInSitemapAttribute), true).Any())
                                        .Where(method => !method.GetCustomAttributes(typeof(ExcludeFromSitemapAttribute), true).Any());
                foreach (var method in methods)
                {
                    sitemapContent += "<url>";

                    var action = method.Name.ToLower();
                    var ctrl = controller.Name.ToLower().Replace("controller", "");
                    var route = rootUrl + urlHelper.Action(action, ctrl).TrimEnd('/'); // Generate correct route with mvc router

                    sitemapContent += $"<loc>{route}</loc>";
                    //sitemapContent += string.Format("<lastmod>{0}</lastmod>", DateTime.UtcNow.ToString("yyyy-MM-dd")); // I didn't want this but uncomment if required
                    sitemapContent += "</url>";
                }
            }
            sitemapContent += "</urlset>";

            _sitemapContent = sitemapContent;
        }
        return _sitemapContent;
    }
}

public class IncludeInSitemapAttribute : Attribute { }
public class ExcludeFromSitemapAttribute : Attribute { }

Usage.cs

public class HomeController : Controller {

  private readonly string _rootUrl;

  public HomeController(string rootUrl) {
      _rootUrl = rootUrl;
  }

  [Route("sitemap.xml")]
  [ExcludeFromSitemap]
  public ContentResult Sitemap(string id) => Content(SitemapGenerator.Generate(_rootUrl, Url), "application/xml");
  
  [IncludeInSitemap] // Include individual action
  public IActionResult Index() => View();
  
  [ExcludeFromSitemap] // Exclude individual action
  public IActionResult Secret() => View();
}

[ExcludeFromSitemap] // all actions will be excluded
public PrivateController : Controller {
    public IActionResult Private1() => View();
    public IActionResult Private2() => View();
    public IActionResult Private3() => View();
}

[IncludeInSitemap] // all actions will be included
public PublicController : Controller {
    public IActionResult Public1() => View();
    public IActionResult Public2() => View();
    public IActionResult Public3() => View();
}