Function valid_oam_label 

pub fn valid_oam_label(label: (&String, &String)) -> bool

This function validates that a key/value pair is a valid OAM label. It’s using fairly basic validation rules to ensure that the manifest isn’t doing anything horribly wrong. Keeping this function free of regex is intentional to keep this code functional but simple.

See https://github.com/oam-dev/spec/blob/master/metadata.md#metadata for details