Headers can't be added by matching against response matchers

[lilnasy]

Caddyfile:

example.com:443 {
	route {
		@success status 2xx
		header @success Cache-Control "public, max-age=3600"
		file_server {
			root /www
		}
	}
}

Error:

Error: adapting config using caddyfile: getting matcher module 'status': module not registered: http.matchers.status

Since Chrome caches 404 responses, I want to add the Cache-Control response header only when the response status is ok (2xx).

I looked at Response Matchers (Caddyfile) -- Caddy documentation, which documents the response matcher above, and combined that with the header directive as documented in header (Caddyfile directive) -- Caddy documentation, but counterintuitively, header can only use request matchers.

encode (Caddyfile directive) -- Caddy documentation leads to believe that response matchers can only be used in specific places, not in a named matcher (is the response matcher example out of date?). However, since both the header directive and the encode directive act on pre-existing responses, it's natural that both can match using response matchers, not just encode.

A caddy community help post (Header only on successful response) suggests a workaround using php_fastcgi. However, that makes the Caddyfile unreadable and opaque since my application really has nothing to do with PHP.

[francislavoie]

You can use intercept for this

[lilnasy]

Thanks, that helps a lot!

Is there a limitation preventing header from working similarly to encode?

[francislavoie]

I'm not sure what you mean. They do completely different things.

The header directive's job is to manipulate response headers. It takes a request matcher, just like every other directive. That's it.

The encode directive enables compression, and it takes a request matcher as well. But because only some content types should be compressed, and we only know the content type after the handler that writes the response is done its job, it also has a response matcher option (with a good default).

They have completely different responsibilities.

[lilnasy]

Thanks for the reply. I should clarify, what I meant to ask was, could header use a response matcher in the same that encode does. After looking at the source code, I learned that not only it can, but it already does!

For example, the following json configuration matches 2xx responses:

{
    "handler": "headers",
    "response": {
        "require": {
            "status_code": [
                2
            ]
        },
        "set": {
            "Cache-Control": [
                "public, max-age=3600"
            ]
        }
    }
},

• This functionality has existed since the 2.0 release, after being added in bf54615.
• The "limitation" was specifically in the caddyfile adapter which didn't have a syntax for emitting the above configuration. This syntax is what I've added in a PR: header: match subdirective for response matching #6765.