* example this converts `☃.net` to `xn--n3h.net`, and `WwW.GoOgLe.cOm` to `www.google.com`.
 * `null` will be returned if the host cannot be ToASCII encoded or if the result contains
 * unsupported ASCII characters.
 */
internal fun String.toCanonicalHost(): String? {
  val host: String = this

  // If the input contains a :, it’s an IPv6 address.
  if (":" in host) {

    fun add(
      name: String,
      value: String,
    ) = commonAdd(name, value)

    /**
     * Add a header with the specified name and value. Does validation of header names, allowing
     * non-ASCII values.
     */
    fun addUnsafeNonAscii(
      name: String,
      value: String,
    ) = apply {
      headersCheckName(name)
      addLenient(name, value)
    }

    /**

    /** Arbitrary code point that's 4 bytes in UTF-8 and valid in IdnaMappingTable.txt. */
    private const val UNICODE_4 = 0x1d11e

    /**
     * Returns a new instance configured with a default encode set for the ASCII range. The specific
     * rules vary per-component: for example, '?' may be identity-encoded in a fragment, but must be
     * percent-encoded in a path.
     *
     * See https://url.spec.whatwg.org/#percent-encoded-bytes

      // Try to parse the whole port string as a number.
      // Java accepts leading plus signs. We don't want to.
      checkArgument(
          !portString.startsWith("+") && CharMatcher.ascii().matchesAllOf(portString),
          "Unparseable port number: %s",
          hostPortString);
      try {
        port = Integer.parseInt(portString);
      } catch (NumberFormatException e) {

			// the parser is more liberal than what USTAR actually permits.
			notASCII := func(r rune) bool { return r >= 0x80 }
			if bytes.IndexFunc(tr.blk[:], notASCII) >= 0 {
				hdr.Format = FormatUnknown // Non-ASCII characters in block.
			}
			nul := func(b []byte) bool { return int(b[len(b)-1]) == 0 }
			if !(nul(v7.size()) && nul(v7.mode()) && nul(v7.uid()) && nul(v7.gid()) &&

var makeFieldsInputASCII = func() []byte {
	x := make([]byte, 1<<20)
	// Input is ~10% space, rest ASCII non-space.
	for i := range x {
		if rand.Intn(10) == 0 {
			x[i] = ' '
		} else {
			x[i] = 'x'
		}
	}
	return x
}

var bytesdata = []struct {
	name string
	data []byte
}{
	{"ASCII", makeFieldsInputASCII()},
	{"Mixed", makeFieldsInput()},
}

            writer: DerWriter,
            value: String,
          ) = writer.writeUtf8(value)
        },
    )

  /**
   * Based on International Alphabet No. 5. Note that there are bytes that IA5 and US-ASCII
   * disagree on interpretation.
   *
   * TODO(jwilson): constrain to IA5 characters.
   */
  val IA5_STRING =
    BasicDerAdapter(
      name = "IA5 STRING",

            }
          }
        }
      }
    }
  }

  @AndroidIncompatible // slow
  @GwtIncompatible // Doubles.tryParse
  public void testTryParseAllCodePoints() {
    // Exercise non-ASCII digit test cases and the like.
    char[] tmp = new char[2];
    for (int i = Character.MIN_CODE_POINT; i < Character.MAX_CODE_POINT; i++) {
      Character.toChars(i, tmp, 0);

                    return;
                }
            }
            else { /* Basic */
                String auth = new String(Base64.decode(msg.substring(6)), "US-ASCII");
                int index = auth.indexOf(':');
                String user = ( index != -1 ) ? auth.substring(0, index) : auth;
                String password = ( index != -1 ) ? auth.substring(index + 1) : "";

                    return;
                }
            } else { /* Basic */
                String auth = new String( Base64.decode( msg.substring(6) ), "US-ASCII" );
                int index = auth.indexOf( ':' );
                String user = (index != -1) ? auth.substring(0, index) : auth;
                String password = (index != -1) ? auth.substring(index + 1) : "";