maskCursor.close()
      }
    } else {
      sinkBuffer.writeByte(b1)
      sinkBuffer.write(payload)
    }

    sink.flush()
  }

  @Throws(IOException::class)
  fun writeMessageFrame(
    formatOpcode: Int,
    data: ByteString,
  ) {
    if (writerClosed) throw IOException("closed")

    messageBuffer.write(data)

    var b0 = formatOpcode or B0_FLAG_FIN