Surrogate Keys not working with otter

Hello! I'm trying to understand how to use surrogate keys and can't seem to get it to work by merely following the spec.

My use-case is that I need to associate a group of cached files with a "project ID" so I can purge all files for the project when it is modified. I'm using Caddy and Otter.

Here's my Caddy config (using github.com/darkweak/souin/plugins/caddy@v1.7.2)

{
    cache {
        ttl 300s
        max_cacheable_body_bytes 1000000
        otter
        api {
            souin
        }
        # This may be required to enable surrogate-keys? https://github.com/darkweak/souin/issues/306#issuecomment-1429744951
        cdn {
            dynamic
            provider souin
        }
        default_cache_control public
    }
}

localhost {
    route {
        cache
        reverse_proxy web:3000
    }
}

When I want to set a surrogate-key, I include the header in the response in my application code (web:3000):

$ curl -ik -H "Host: picouser-www.localhost" https://localhost                        
HTTP/2 200 
alt-svc: h3=":443"; ma=2592000
cache-control: public
cache-status: Souin; fwd=uri-miss; stored; key=GET-https-picouser-www.localhost-/
content-security-policy: script-src 'self'
content-type: text/html
date: Tue, 22 Oct 2024 02:16:29 GMT
etag: 5fddc78468241bf0dc7e721867874288
last-modified: Mon, 21 Oct 2024 20:21:37 GMT
server: Caddy
strict-transport-security: max-age=31536000; preload
surrogate-key: picouser-www                                <------ Project ID surrogate key is set here
x-frame-options: DENY
content-length: 2051

But the surrogate key is never saved:

$ curl 'https://localhost/souin-api/souin/surrogate_keys' | jq
{
  "GET-https-picouser-www.localhost-/": "<omitted>",
  "IDX_GET-https-picouser-www.localhost-/": "\n�\u0001\n\"GET-https-picouser-www.localhost-/\u0012k\n\u000b\b��ܸ\u0006\u0010���Y\u0012\n\b��ܸ\u0006\u0010��\u0004\u001a\n\b��ܸ\u0006\u0010��\u0004* 5fddc78468241bf0dc7e7218678742882\"GET-https-picouser-www.localhost-/"
}

Likewise, purging via the surrogate key I set also does not clear this cache entry.

I searched through the code and is seems like what I'm doing should work, but I may be missing a config value or something: https://github.com/darkweak/souin/blob/2968d51eef04b31925352ac4aaf815ea49f4efbd/pkg/surrogate/providers/common.go#L238

Am I using the feature incorrectly? Or could there be a bug? Happy to provide further info!

darkweak / souin

Surrogate Keys not working with otter #563