Properties from file system should be search with the same rules used for environment variables

[kifj]

Statement of problem

given a interface for the MicroProfile REST client

package com.example;
@Produces(APPLICATION_JSON)
@RegisterRestClient
public interface QuickQuoteService {
  ...
}

which will retrieve its URL from MP Config with the key

com.example.QuickQuoteService/mp-rest/url

and a ConfigMap in Kubernetes with entries

kind: ConfigMap
data:
 com_example_QuickQuoteService_mp_rest_url: https://quote.cnbc.com/quote-html-webservice

A ConfigMap defines rules on the key, which forbids '/', because it cannot be mapped to an environment variable or a file name.

According to specification the replacement rules are defined for environment variables, all non-alphanumeric characters are replaced with '_'; and if that doesn't resolve, all alphabetical characters can be upper-case.

This ConfigMap will be mounted in a volume, resulting in a file named com_example_QuickQuoteService_mp_rest_url with the value as content.

The FileSystemConfigSource should pick up that file (which it does) and the Config should return its content as value for the key com.example.QuickQuoteService/mp-rest/url (which is doesn't)

Solution

The mapping rules for environment variables (see EnvConfigSource) should apply to file names as well, even if the specification does not define this behavior.

[radcortez]

Hi @kifj

Thank yo for the PR!

Just a clarification: from my understanding, the spec only mandates the name mapping to happen for Environment Variables: https://github.com/eclipse/microprofile-config/blob/cafee0a79fd36dfaa4f7b30bc77efa75eefa589b/spec/src/main/asciidoc/configsources.asciidoc#L53

Now, that doesn't mean we shouldn't support this in the FileSystemConfigSource :)

Do you mind adding a few tests?

[radcortez]

Add tests.

[kifj]

You're right regarding the specification so I have updated the comment and added a unit test

[radcortez]

Thanks!

Can you also document the new feature for FileSystemConfigSource here:
https://github.com/smallrye/smallrye-config/blob/9a7716257d73881f44ab1d9dda466135967df278/doc/modules/ROOT/pages/config-sources/filesystem-config-source.adoc?