return -1;
            }
            readChars++;
            char ch = (char) readChar;
            if (paddingChar != null && paddingChar.charValue() == ch) {
              if (!hitPadding
                  && (readChars == 1 || !alphabet.isValidPaddingStartPosition(readChars - 1))) {
                throw new DecodingException("Padding cannot start at index " + readChars);
              }
              hitPadding = true;

    // Get frame length, optionally reading from follow-up bytes if indicated by special values.
    frameLength = (b1 and B1_MASK_LENGTH).toLong()
    if (frameLength == PAYLOAD_SHORT.toLong()) {
      frameLength = (source.readShort() and 0xffff).toLong() // Value is unsigned.
    } else if (frameLength == PAYLOAD_LONG.toLong()) {
      frameLength = source.readLong()
      if (frameLength < 0L) {
        throw ProtocolException(