Send Bytes and String via BLE / Translation Java - Swift

Question

I'm sending Strings from Mobile Device via BLE to an specific Hardware. Depending on the version, a header byte must be prepended (0x01). My working Java version (Android) looks like this:

   private void writeBluetooth(String msg){

        this.btResponseHandler.postDelayed(btResponseHandlerRunnableCode, 500);
        if (xBleHardwareVersion == 1)
        {
            byte[] result = concat(msg.getBytes(), new byte[] { 0x0d, 0x0a });
            peripheral.writeCharacteristic(V1_SERVICE_UUID,V1_TX_CHARACTERISTIC,result, WriteType.WITHOUT_RESPONSE);
        } else if (xBleHardwareVersion == 2) {
            byte[] result = concat(new byte[] { 0x01 }, msg.getBytes(), new byte[] { 0x0d, 0x0a });
            peripheral.writeCharacteristic(V2_SERVICE_UUID,V2_TX_CHARACTERISTIC,result, WriteType.WITHOUT_RESPONSE);
        }
    }

I'm very new at the Swift language so my question: How to get this word with Swift on IOS?

Best regards