val reservedFlag3 = b0 and B0_FLAG_RSV3 != 0
    if (reservedFlag3) throw ProtocolException("Unexpected rsv3 flag")

    val b1 = source.readByte() and 0xff

    val isMasked = b1 and B1_FLAG_MASK != 0
    if (isMasked == isClient) {
      // Masked payloads must be read on the server. Unmasked payloads must be read on the client.
      throw ProtocolException(