# File lib/rubygems/package.rb, line 48
  def self.open(io, mode = "r", signer = nil, &block)
    tar_type = case mode
               when 'r' then TarInput
               when 'w' then TarOutput
               else
                 raise "Unknown Package open mode"
               end

    tar_type.open(io, signer, &block)
  end