ripta/drydock

module Drydock
  # A subclass of the rubygems `TarWriter` used to produce a tar stream.
  class TarWriter < ::Gem::Package::TarWriter

    # Adds file `name` with permissions `mode` and modification time `mtime`
    # to the stream. Yields a write-only IO that cannot be rewound.
    #
    # @param [String] name the filename
    # @param [Integer] mode the file mode in octal, e.g., 0644
    # @param [Time] mtime the modification time of the file
    # @yield [Gem::Package::TarWriter::RestrictedStream]
    def add_entry(name, mode: 0644, mtime: Time.now, _uid: 0, _gid: 0)
      check_closed

      fail 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: mtime
      )
      @io.write header
      @io.pos = final_pos

      self
    end

  end
end