class Gem::Package::TarReader::Entry

def self.open(header, io, &block)
  entry = new header, io
  return entry unless block_given?
  begin
    yield entry
  ensure
    entry.close
  end
end

def bytes_read
  @read
end

def check_closed # :nodoc:
  raise IOError, "closed #{self.class}" if closed?
end

def close
  return if closed?
  # Seek to the end of the entry if it wasn't fully read
  seek(0, IO::SEEK_END)
  # discard trailing zeros
  skip = (512 - (@header.size % 512)) % 512
  @io.read(skip)
  @closed = true
  nil
end

def closed?
  @closed
end

def directory?
  @header.typeflag == "5"
end

def eof?
  check_closed
  @read >= @header.size
end

def file?
  @header.typeflag == "0"
end

def full_name
  @header.full_name.force_encoding(Encoding::UTF_8)
rescue ArgumentError => e
  raise unless e.message == "string contains null byte"
  raise Gem::Package::TarInvalidError,
        "tar is corrupt, name contains null byte"
end

def getc
  return nil if eof?
  ret = @io.getc
  @read += 1 if ret
  ret
end

def initialize(header, io)
  @closed = false
  @header = header
  @io = io
  @orig_pos = @io.pos
  @end_pos = @orig_pos + @header.size
  @read = 0
end

def pos
  check_closed
  bytes_read
end

def pos=(new_pos)
  seek(new_pos, IO::SEEK_SET)
end

def read(maxlen = nil)
  if eof?
    return maxlen.to_i.zero? ? "" : nil
  end
  max_read = [maxlen, @header.size - @read].compact.min
  ret = @io.read max_read
  if ret.nil?
    return maxlen ? nil : "" # IO.read returns nil on EOF with len argument
  end
  @read += ret.size
  ret
end

def readpartial(maxlen, outbuf = "".b)
  if eof? && maxlen > 0
    raise EOFError, "end of file reached"
  end
  max_read = [maxlen, @header.size - @read].min
  @io.readpartial(max_read, outbuf)
  @read += outbuf.size
  outbuf
end

def rewind
  check_closed
  seek(0, IO::SEEK_SET)
end

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

def size
  @header.size
end

def symlink?
  @header.typeflag == "2"
end