Following up on this, it turns out that you may not need the Middleware to route the request to a controller, you could use the [Route] attribute. No need for registration in the Startup class.

Something like this...

using Microsoft.AspNetCore.Mvc;

namespace Our.Umbraco.Web.Controllers;

public class FaviconIcoController : Controller
{
    private readonly IWebHostEnvironment _webHostEnvironment;

    public FaviconIcoController(IWebHostEnvironment webHostEnvironment)
    {
        _webHostEnvironment = webHostEnvironment;
    }

    [Route("/favicon.ico")]
    public IActionResult Index()
    {
        var hostname = Request.Host.Host;
        var path = Path.Combine(_webHostEnvironment.WebRootPath, $"{hostname}.ico");

        if (System.IO.File.Exists(path) == true)
        {
            var bytes = System.IO.File.ReadAllBytes(path);
            return File(bytes, "image/x-icon");
        }

        return NotFound("favicon.ico not found");
    }
}

Please note that the [Route] attribute only works if the physical file for "favicon.ico" does NOT exist, otherwise the static file provider will kick in and serve that before it hits the controller.

Hack the code as you'd need.

Hope this helps.

Cheers,
- Lee

Interesting response Lee. Can you wildcard the Route? So say if you wanted to catch all requests for a certain file type e.g. stp?

Hi Brendan,

I'd assume it'd work - as it's pretty much routing a request, but the same logic applies that if a physical file with the same name exists, then then static file provider would pick it up first.

My only caveat would be that I'm not familiar with the *.stp file extension, so don't know if a MIME type would need to be configured beforehand.

Cheers,
- Lee