# File lib/png/reader.rb, line 34
  def self.read_chunk expected_type, png
    size, type = png.slice!(0, 8).unpack 'Na4'
    data, crc = png.slice!(0, size + 4).unpack "a#{size}N"

    check_crc type, data, crc

    raise ArgumentError, "Expected #{expected_type} chunk, not #{type}" unless
      type == expected_type

    return data
  end