private val maskCursor: Buffer.UnsafeCursor? = if (isClient) null else Buffer.UnsafeCursor()

  interface FrameCallback {
    @Throws(IOException::class)
    fun onReadMessage(text: String)

    @Throws(IOException::class)
    fun onReadMessage(bytes: ByteString)

    fun onReadPing(payload: ByteString)

    fun onReadPong(payload: ByteString)

    fun onReadClose(
      code: Int,
      reason: String,

  @Synchronized fun receivedPongCount(): Int = receivedPongCount

  @Throws(IOException::class)
  override fun onReadMessage(text: String) {
    listener.onMessage(this, text)
  }

  @Throws(IOException::class)
  override fun onReadMessage(bytes: ByteString) {
    listener.onMessage(this, bytes)
  }

  @Synchronized override fun onReadPing(payload: ByteString) {