Wouldn't it be better to use the error routes instead? ala https://github.com/caddyserver/caddy/pull/4076/files#diff-08835e4955ebc248e067238c368ac226eb8b44742ee4b04400ddb5f1e550cb47R268-R284

Unfortunately I don't think so, because I don't think error routes will let you keep the same error code if you're serving a file with file_server.

But either way, that would be pretty roundabout... reverse_proxy -> handle_response -> error -> handle_errors -> file_server? It would be better to cut out error and handle_errors and leave that to actually be for errors produced by Caddy.

This is still useful in other situations though, e.g. if you want to serve a "maintenance mode" page with a specific status, without emitting error, etc. Forcing users to use error -> handle_errors seems unwise, when they would just want a quick "respond with a file with X status code" based on some matcher decision.

Why did we add the errors directive then if we don't want people to use it? The whole point is to consolidate error handling.

I'm saying those are separate but valid usecases. The times where you use error are not necessarily the same as those you'd want to just serve a file with a specific status.

Here's an example of how it would look when paired with handle_response:

example.com {
	reverse_proxy localhost:8080 {
		@fourhundred status 4xx
		handle_response @fourhundred {
			root * /path/to/errors
			rewrite * /{http.reverse_proxy.status_code}.html
			file_server {
				status {http.reverse_proxy.status_code}
			}
		}
	}
}

But if it had to be done with error, it would look like this (way more complicated to reason about):

example.com {
	reverse_proxy localhost:8080 {
		@fourhundred status 4xx
		handle_response @fourhundred {
			error {http.reverse_proxy.status_text} {http.reverse_proxy.status_code}
		}
	}

	handle_errors {
		@fourhundred expression {http.error.status_code} >= 400 && {http.error.status_code} <= 499
		handle @fourhundred {
			root * /path/to/errors
			rewrite * /{http.error.status_code}.html
			file_server
		}
	}
}

And that assumes that file_server will still write the 4xx status in the 2nd example due to being in the error handler chain. I'm not certain that it does, I think it'll write a 200 status anyways.

Another example usecase for this https://caddy.community/t/serving-a-single-static-file-that-matches-multiple-paths-with-a-http-status-code-of-410/12072