flatten.rb

module Fluent
  class TextParser
    class StringifiedValuesJSONParser < JSONParser
      Plugin.register_parser("stringified_values_json", self)

      def parse(text)
        time, record = super(text)

        # replace all Hash (like a dict) values with stringified JSON
        record = record.inject({}) { | new_hash, (key, value) |
            if value.is_a?(Hash)
              new_hash[key] = JSON.dump(value)
            else
              new_hash[key] = v
            end
            new_hash
        }
        
        yield time, record
      end
    end
  end
end