tar-gz-each.rb

require 'zlib'
require 'benchmark'
require 'rubygems/package'
require 'rubygems/package/tar_reader'

duration = Benchmark.realtime do
  tar = Gem::Package::TarReader.new(Zlib::GzipReader.open(ARGV.first))
  tar.each { |_| }
end

p duration

class Gem::Package::TarReader
  def each
    return enum_for __method__ unless block_given?

    use_seek = @io.respond_to?(:seek)

    until @io.eof? do
      header = Gem::Package::TarHeader.from @io
      return if header.empty?

      entry = Gem::Package::TarReader::Entry.new header, @io
      size = entry.header.size

      yield entry

      skip = (512 - (size % 512)) % 512
      pending = size - entry.bytes_read

      if use_seek
        begin
          # avoid reading if the @io supports seeking
          @io.seek pending, IO::SEEK_CUR
          pending = 0
        rescue Errno::EINVAL
        end
      end

      # if seeking didn't work
      while pending > 0 do
        bytes_read = @io.read([pending, 4096].min).size
        raise UnexpectedEOF if @io.eof?
        pending -= bytes_read
      end

      @io.read skip # discard trailing zeros

      # make sure nobody can use #read, #getc or #rewind anymore
      entry.close
    end
  end
end

duration = Benchmark.realtime do
  tar = Gem::Package::TarReader.new(Zlib::GzipReader.open(ARGV.first))
  tar.each { |_| }
end

p duration