UTF-8: Implement support in Ruby client library

[ywwg]

As in prometheus/client_golang#1369 and prometheus/client_java#916, the Ruby client library needs to be updated to support UTF-8.

Tasks:

• Add flag to enable change in validation logic to check that metric and label names are UTF-8 valid instead of the old letters/numbers/underscores/colons set
• Update exposition format parsers for the new syntax
• Update PromQL parsers (if any) for the new syntax
• Update content negotiation logic

For background and references see prometheus/prometheus#13095

[Sinjo]

Hey, thanks for the heads up. I've got a rough idea in my head of how those changes will fit into the codebase.

I've given the proposal a read and one thing that stuck out to me is that grouping key labels in the pushgateway client's code aren't mentioned. Are they sticking to the old rules for now?

[beorn7]

Very good point. We haven't thought about PGW yet.
That needs more code changes, and some more ideas. sigh

[beorn7]

For now, I would assume the PGW doesn't support the new UTF-8 names yet.

[ywwg]

We are making a note to create a design for this situation

[Sinjo]

That needs more code changes, and some more ideas. sigh

Happy to be of service 🙈