val c = this[i]
    // The WHATWG Host parsing rules accepts some character codes which are invalid by
    // definition for OkHttp's host header checks (and the WHATWG Host syntax definition). Here
    // we rule out characters that would cause problems in host headers.
    if (c <= '\u001f' || c >= '\u007f') {
      return true
    }
    // Check for the characters mentioned in the WHATWG Host parsing spec:

   0080-009F; [CONTROL CHARACTERS]
   06DD; ARABIC END OF AYAH
   070F; SYRIAC ABBREVIATION MARK
   180E; MONGOLIAN VOWEL SEPARATOR
   200C; ZERO WIDTH NON-JOINER
   200D; ZERO WIDTH JOINER
   2028; LINE SEPARATOR
   2029; PARAGRAPH SEPARATOR
   2060; WORD JOINER
   2061; FUNCTION APPLICATION
   2062; INVISIBLE TIMES
   2063; INVISIBLE SEPARATOR
   206A-206F; [CONTROL CHARACTERS]
   FEFF; ZERO WIDTH NO-BREAK SPACE

  }

  /**
   * Strip unexpected characters when converting to URI (which is more strict).
   * https://github.com/square/okhttp/issues/5667
   */
  @Test
  fun hostToUriStripsCharacters() {
    val httpUrl = "http://example\".com/".toHttpUrl()
    assertThat(httpUrl.toUri().toString()).isEqualTo("http://example.com/")
  }

  /** Confirm that URI retains other characters. https://github.com/square/okhttp/issues/5236 */
  @Test

 *
 * This implementation is optimized for readability over efficiency.
 *
 * This implements non-transitional processing by preserving deviation characters.
 *
 * This implementation's STD3 rules are configured to `UseSTD3ASCIIRules=false`. This is
 * permissive and permits the `_` character.
 *
 * [mapping table]: https://www.unicode.org/reports/tr46/#IDNA_Mapping_Table
 * [mapping step]: https://www.unicode.org/reports/tr46/#ProcessingStepMap

  @Test fun mixedCasePunycode() {
    testDecodeOnly(
      unicode = "ليهمابتكلموشعربي؟",
      punycode = "Xn--EgBpDaJ6Bu4bXfGeHfVwXn",
    )
  }

  /**
   * It's invalid to have a label longer than 63 characters. If that's requested, the encoder may
   * overflow and return null.
   */
  @Test fun overflowEncodingOversizedLabel() {
    val a1000 = "a".repeat(1000)
    val a1000MaxCodePoint = a1000 + "\udbff\udfff"

    // Host names are special:
    //
    //  * Several characters are forbidden and must throw exceptions if used.
    //  * They don't use percent escaping at all.
    //  * They use punycode for internationalization.
    //  * URI is much more strict than HttpUrl or URL on what's accepted.
    //
    // HttpUrl is quite lenient with what characters it accepts. In particular, characters like '{'

      if (prefix.exhausted()) {
        break
      }
      val codePoint = prefix.readUtf8CodePoint()
      if (Character.isISOControl(codePoint) && !Character.isWhitespace(codePoint)) {
        return false
      }
    }
    return true
  } catch (_: EOFException) {
    return false // Truncated UTF-8 sequence.
  }

}

/**
 * Returns the next index in this at or after [startIndex] that is a character from
 * [characters]. Returns the input length if none of the requested characters can be found.
 */
private fun String.indexOfElement(
  characters: String,
  startIndex: Int = 0,
): Int {
  for (i in startIndex until length) {
    if (this[i] in characters) {
      return i
    }
  }
  return length

 * units away from 0 and 0.499 towards 0. The smallest unit this returns is "µs"; the largest unit
 * it returns is "s". For values in [-499..499] this returns "  0 µs".
 *
 * The returned string attempts to be column-aligned to 6 characters. For negative and large values
 * the returned string may be longer.
 */
fun formatDuration(ns: Long): String {
  val s =
    when {
      ns <= -999_500_000 -> "${(ns - 500_000_000) / 1_000_000_000} s "

      verifyHostname(hostname, it)
    }
  }

  /**
   * This is like [toLowerCase] except that it does nothing if this contains any non-ASCII
   * characters. We want to avoid lower casing special chars like U+212A (Kelvin symbol) because
   * they can return ASCII characters that match real hostnames.
   */
  private fun String.asciiToLowercase(): String {
    return when {