func readFull(r io.Reader, buf []byte) error {
	_, err := io.ReadFull(r, buf)
	if err == io.EOF {
		return io.ErrUnexpectedEOF
	}
	return err
}
func readFull(r io.Reader, buf []byte) error {
	_, err := io.ReadFull(r, buf)
	if err == io.EOF {
		return io.ErrUnexpectedEOF
	}
	return err
}
// readFull wraps io.ReadFull to return io.ErrUnexpectedEOF instead
// of io.EOF when 0 bytes are read.