Some bag code for Hydra. Uses https://github.com/no-reply/bagit

baggable.rb

require 'bagit'

module Hybag
  module Baggable

    def write_bag(path = '')
      raise Exception if self.pid == '__DO_NOT_USE__'

      # delete any existing bags before making a new one                                                                                                                 
      self.delete_bag(path)

      path = bag_dir(path)

      FileUtils.mkdir_p path unless File.directory? path
      bag = BagIt::Bag.new(path)

      #TODO: Writing to bag files is naive; reads file out and writes it.                                                                                                
      #      Possibly there is a better way to do this.                                                                                                                  

      # add the datastreams to the bag, then manifest                                                                                                                    
      datastreams.each do |label, ds|
        unless ds.content.nil?
          label = label + mime_extension(ds)
          if bag_contents.include? ds
            bag.add_file(label) { |f|
              f.puts ds.content
            }
          elsif bag_tags.include? ds
            bag.add_tag_file(label) { |f|
              f.puts ds.content
            }
          elsif bag_fedora_tags.values.include? ds
            bag.add_tag_file('fedora/' + label) { |f|
              f.puts ds.content
            }
          end
        end
      end

      bag.manifest!
      return bag
    end
    # just an alias for the export job's perform method against self                                                                                                     
    def queue_bag_export(path = '')
      Resque.enqueue(Exporter, self.pid, path)
    end

    def delete_bag(path = '')
      bag_path = bag_dir(path)
      FileUtils.rm_rf bag_path if File.directory? bag_path
    end

    private

    # create a safe cross-platform bag path                                                                                                                              
    def bag_dir(path)
      # TODO:  make bag directory configurable?                                                                                                                          
      path = Rails.root.join("tmp/bags", path) unless path.to_s.starts_with? Rails.root.join("tmp/bags").to_s
      return File.join(path, self.pid).gsub(/:/, "_")
    end

    #TODO: allow selection of specific content datastreams to bag                                                                                                        
    #      to ignore thumbnails and other derivitives, for example.                                                                                                      

    # return all content files for bag                                                                                                                                   
    def bag_contents
      self.datastreams.reject { |label, ds| bag_tags.include?(label) or bag_fedora_tags.include?(label) }
    end

    # return all non-fedora tag files                                                                                                                                    
    def bag_tags
      self.metadata_streams
    end

    # return fedora tag files                                                                                                                                            
    def bag_fedora_tags
      self.datastreams.select { |label, ds| ds.is_a?(ActiveFedora::RelsExtDatastream) or ds.dsid == "DC"}
    end

    def mime_extension(ds)
      if ds.kind_of?(ActiveFedora::NtriplesRDFDatastream)
        ext = 'nt'
      else
        ext = MIME::Types[ds.mimeType].first.extensions[0]
      end
      return '.' + ext
    end

  end
end

exporter.rb

module Hybag
  class Exporter
    @queue = :hybag_export

    def self.perform(id, path='')
      object = ActiveFedora::Base.find(id).adapt_to_cmodel
      object.write_bag(path)
    end

  end
end