Filter example2: add tag and time like existence mixins

filter_add_metadata.rb

module Fluent
  class AddMetadataFilter < Filter
    Plugin.register_filter('add_metadata', self)

    config_param :include_time_key, :bool, :default => false
    config_param :time_key, :string, :default => 'time'
    config_param :time_format, :string, :default => nil
    config_param :include_tag_key, :bool, :default => false
    config_param :tag_key, :string, :default => 'tag'
    config_param :localtime, :bool, :default => true

    def configure(conf)
      super

      if conf['utc']
        @localtime = false
      end
      @timef = TimeFormatter.new(@time_format, @localtime)
    end

    def filter(tag, time, record)
      if @include_tag_key
        record[@tag_key] = tag
      end
      if @include_time_key
        record[@time_key] = @timef.format(time)
      end
      record
    end
  end if defined?(Filter) # Avoid 'uninitialized constant Fluent::Filter' at Fluentd v0.10
end