*     [Section 7.4 of RFC 6455](http://tools.ietf.org/html/rfc6455#section-7.4) or `0`.
   * @param reason Reason for shutting down or `null`.
   */
  @Throws(IOException::class)
  fun writeClose(
    code: Int,
    reason: ByteString?,
  ) {
    var payload = ByteString.EMPTY
    if (code != 0 || reason != null) {
      if (code != 0) {
        validateCloseCode(code)
      }
      payload =