Trying to create a gzip filter for rake-pipeline

Assetfile.rb

class GzipFilter < Rake::Pipeline::Filter
  processes_binary_files
  def generate_output(inputs, output)
    inputs.each do |input|
      strio = StringIO.open('','w')
      gz = Zlib::GzipWriter.new(strio)
      gz.write(input.read)
      gz.close
      output.write strio.string
    end
  end
end