class Gem::Package::TarWriter

def add_file(name, mode) # :yields: io

:yields: io 
def add_file(name, mode) # :yields: io
  check_closed
  raise Gem::Package::NonSeekableIO unless @io.respond_to? :pos=
  name, prefix = split_name name
  init_pos = @io.pos
  @io.write "\0" * 512 # placeholder for the header
  yield RestrictedStream.new(@io) if block_given?
  size = @io.pos - init_pos - 512
  remainder = (512 - (size % 512)) % 512
  @io.write "\0" * remainder
  final_pos = @io.pos
  @io.pos = init_pos
  header = Gem::Package::TarHeader.new :name => name, :mode => mode,
                                       :size => size, :prefix => prefix,
                                       :mtime => Time.now
  @io.write header
  @io.pos = final_pos
  self
end