code: def get_matching_prefix(self, namespace, stream):
      
      validate_stream(stream)
      default_prefix = ''
      longest_prefix = default_prefix
      for prefix in self.prefix_confs[namespace]:
        if prefix == default_prefix:
          continue
        if not stream.startswith(prefix):
          continue
        if len(prefix) <= len(longest_prefix):
          continue
        longest_prefix = prefix
      return longest_prefix
docs: We look at the stream prefixs configured in stream.yaml and match stream
      to the longest prefix.