[Solved] Redirect locally non existing files to another domain using part of uri

[gjwnc (None)]

I have a Caddyfile which has default rewrite configured:

rewrite {
      to {path} {path}/ /index.php?{query}
}

Now I want to redirect requests to a directory to another server if the file is not available local.
My current testing config looks like this:

   # use previous behaviour if not a request to the resources directory
   rewrite {
      if {path} not_match ^\/resources
      to {path} {path}/ /index.php?{query}
    }
    # extract the last part of the resources directory if the file doesnt exist
    rewrite {
        r ^/resources/(.*)$
        to {path} /{1}
    }
    # finally redirect requests to /resources using the rewrite-uri
    redir {
       # Modify the destination and status as required
       /resources https://media.mycdn.org/{rewrite-uri} 307
    }

The result is, that files which are available in my local resources directory are served correctly, but non existing files don’t redirect, but return 404.
I tried a few configs, but I dont see how the rewrite/redir play together here.

[Whitestrake (Matthew Fay)]

Hmm. At a guess I’d say it’s because you’re actually rewriting to remove the /resources/ prefix when the file’s not found.

Actually, at a glance, I’d expect that a request for a file inside /resources/ that exists locally would actually be redirected instead of served, with that setup. You’re definitely getting 200s and the file served locally in this case?

Anyway, you can’t really use a base path that you’re expecting to rewrite away from as the base path for your redir. You’ll need to use a blanket redir (because the rewrite could go anywhere), and you can use if to check whether it was rewritten away from /resources/.

I’ve written a few of these before, but this is an example by hand and untested. A few tips for the other components, too.

rewrite {
  to {path} {path}/ /?{query}          # canonical reference to index
}

rewrite /resources/ {                  # use base path to avoid running
  r ^/resources/(.*)$                  # regex on every single request -
  to {path} /{1}                       # longer base path rewrite also
}                                      # wins, no need to exclude above

redir {
  if {uri} not {rewrite_uri}           # check we did rewrite the URI
  if {uri} starts_with /resources/     # specifically, from /resources
  / https://media.mycdn.org/{rewrite-uri} 307
}

[gjwnc (None)]

Many thanks!
I finally got it running with a few changes.

1. rewrite-uri must be changed to rewrite_uri
2. I needed to move the fallback rewrite right at the bottom of the config
3. The rewrite /resources/ { was ignored - thus I changed rewrite {
4. I removed the slash from /{1} since it was leading to a double slash in the redirect

    rewrite {                  # use base path to avoid running
        r ^/resources/(.*)$                  # regex on every single request -
        to {path} {1}                       # longer base path rewrite also
    }                                      # wins, no need to exclude above

    redir {
        if {uri} not {rewrite_uri}           # check we did rewrite the URI
        if {uri} starts_with /resources/     # specifically, from /resources
        / https://media.mycdn.org/{rewrite_uri} 307
    }

    rewrite {
        to {path} {path}/ /index.php?{query}
    }

[Whitestrake (Matthew Fay)]

Good catch on the first one!

The second one is a direct result of the third. When one has a longer base path, it automatically “wins” out of the two, but with identical base paths (the implicit /), ordering becomes important. I’m not sure why it would be ignored, though. Maybe /resources would’ve been a better base path than /resources/?

As for the fourth, I don’t think it’s actually the slash before {1} that’s important. It’s the slash in the middle of media.mycdn.org/{rewrite_uri}, since {rewrite_uri} comes with the prefixed slash. It all comes out in the wash, though.

Glad it’s working for you.