}
	}

	n = len(b0) - len(b)
	switch {
	case err == ErrWriteTooLong:
		return n, errMissData // Not possible; implies bug in validation logic
	case err != nil:
		return n, err
	case sw.logicalRemaining() == 0 && sw.physicalRemaining() > 0:
		return n, errUnrefData // Not possible; implies bug in validation logic
	case overwrite:
		return n, ErrWriteTooLong
	default:
		return n, nil
	}
}

	// valid UTF-8 string, then we set the UTF-8 bit.
	//
	// For the case, where the user explicitly wants to specify the encoding
	// as UTF-8, they will need to set the flag bit themselves.
	utf8Valid1, utf8Require1 := detectUTF8(fh.Name)
	utf8Valid2, utf8Require2 := detectUTF8(fh.Comment)
	switch {
	case fh.NonUTF8:
		fh.Flags &^= 0x800
	case (utf8Require1 || utf8Require2) && (utf8Valid1 && utf8Valid2):
		fh.Flags |= 0x800