Gem::Package::TarReader::Entry#seek

# File tmp/rubies/ruby-3.4.1/lib/rubygems/package/tar_reader/entry.rb, line 188
def seek(offset, whence = IO::SEEK_SET)
  check_closed

  new_pos =
    case whence
    when IO::SEEK_SET then @orig_pos + offset
    when IO::SEEK_CUR then @io.pos + offset
    when IO::SEEK_END then @end_pos + offset
    else
      raise ArgumentError, "invalid whence"
    end

  if new_pos < @orig_pos
    new_pos = @orig_pos
  elsif new_pos > @end_pos
    new_pos = @end_pos
  end

  pending = new_pos - @io.pos

  return 0 if pending == 0

  if @io.respond_to?(:seek)
    begin
      # avoid reading if the @io supports seeking
      @io.seek new_pos, IO::SEEK_SET
      pending = 0
    rescue Errno::EINVAL
    end
  end

  # if seeking isn't supported or failed
  # negative seek requires that we rewind and read
  if pending < 0
    @io.rewind
    pending = new_pos
  end

  while pending > 0 do
    size_read = @io.read([pending, 4096].min)&.size
    raise(EOFError, "end of file reached") if size_read.nil?
    pending -= size_read
  end

  @read = @io.pos - @orig_pos

  0
end