String expected = "www.codelibs.org";
        assertEquals(expected, resolver.toAscii(host));

        host = "テスト.org";
        expected = "xn--zckzah.org";
        assertEquals(expected, resolver.toAscii(host));

        host = "xn--zckzah.org";
        expected = "xn--zckzah.org";
        assertEquals(expected, resolver.toAscii(host));

        host = "%E3%83%86%E3%82%B9%E3%83%88.org";

     * Converts the given host string to ASCII using IDN.
     *
     * @param host the host string to convert
     * @return the ASCII representation of the host string
     */
    protected String toAscii(final String host) {
        return IDN.toASCII(decode(host), flag);
    }

    /**
     * Sets the flag for IDN conversion.
     *
     * @param flag the flag to set
     */
    public void setFlag(final int flag) {

func isASCII(s string) bool {
	for _, c := range s {
		if c >= 0x80 || c == 0x00 {
			return false
		}
	}
	return true
}

// toASCII converts the input to an ASCII C-style string.
// This is a best effort conversion, so invalid characters are dropped.
func toASCII(s string) string {
	if isASCII(s) {
		return s
	}
	b := make([]byte, 0, len(s))
	for _, c := range s {
		if c < 0x80 && c != 0x00 {

			return err // Global headers return here
		}
	}

	// Pack the main header.
	var f formatter // Ignore errors since they are expected
	fmtStr := func(b []byte, s string) { f.formatString(b, toASCII(s)) }
	blk := tw.templateV7Plus(hdr, fmtStr, f.formatOctal)
	blk.setFormat(FormatPAX)
	if err := tw.writeRawHeader(blk, hdr.Size, hdr.Typeflag); err != nil {
		return err
	}