class Gem::Commands::UnpackCommand

def get_metadata path
  format = Gem::Package.new path
  spec = format.spec
  metadata = nil
  open path, Gem.binary_mode do |io|
    tar = Gem::Package::TarReader.new io
    tar.each_entry do |entry|
      case entry.full_name
      when 'metadata' then
        metadata = entry.read
      when 'metadata.gz' then
        metadata = Gem.gunzip entry.read
      end
    end
  end
  return spec, metadata
end