Regex with no existing topics?

[dougmoscrop]

Technically I am using the C# client, but, as far as I can tell it is forwarding the Subscribe call to librdkafka without doing anything that would affect this, so my question is about intended behaviour.

I am trying to subscribe to a regex of topics, generated by Debezium, which look like "foo.bar.{topic}":

consumer.Subscribe("^foo\\.bar\\..*$")

I get the following error:

Error: Subscribed topic not available: ^foo\\.bar\\..*$: Broker: Unknown topic or partition

However, if I use the admin client to first create a topic, like foo.bar.ignored, then Subscribe works fine and the dynamically generated topics (e.g. foo.bar.asdf, foo.bar.qwerty) are detected.

Is this expected, or is this a corner case that is worth filing an issue over?