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Details

Type: Bug
Resolution: Done
Priority: P2: Important
Fix Version/s: 5.15.3, 5.15.4, 5.15, 6.2.0 Alpha
Affects Version/s: 5.15.2
Component/s: SerialBus: MOD Bus
Labels:
None
Environment:
Qt Creator

Platform/s:

Windows
Commits:
2c0bb738e988d84f36169e0103d051745b678479 (qt/qtserialbus/dev) 17ac276e9b4fcde0f2e2b9a68a01ef6cdde31cf5 (qt/tqtc-qtserialbus/tqtc/lts-5.15)

Description

I'm trying to create a custom modbus command. The command is being sent and then received on the other side, the reply is sent back but I always receive an empty invalid reply. The same problem was discussed here - https://bugreports.qt.io/browse/QTBUG-62192

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QObject *connector = new QObject();

    QModbusTcpClient *client = new QModbusTcpClient();
    client->setConnectionParameter(QModbusDevice::NetworkAddressParameter, "127.0.0.1");
    client->setConnectionParameter(QModbusDevice::NetworkPortParameter, 8899);
    client->connectDevice();

    QModbusResponse::registerDataSizeCalculator(QModbusPdu::CustomFun_ReadData, [](const QModbusResponse &)-> int
    {
        qInfo() << "Custom data size calculator"; // this line wasn't printed out
        return 42;
    });

    connector->connect(client, &QModbusClient::stateChanged, connector, [connector, client]()
    {
        if(client->state() == QModbusClient::ConnectedState)
        {
            auto cmd = QModbusPdu::FunctionCode(QModbusPdu::CustomFun_ReadData);
            QModbusRequest request(cmd);
            qInfo() << "Is request valid? " << request.isValid(); // true
            QModbusReply* reply = client->sendRawRequest(request, 1);
            qInfo() << "Reply is null: " << (reply == nullptr); // false
            qInfo() << "Is response valid? " << reply->rawResult().isValid(); // false, we didn't get it yet
 
            connector->connect(reply, &QModbusReply::finished, connector, [reply]()
            {
                qInfo() << "isFinished? " << reply->isFinished(); // true
                qInfo() << "Is response valid? " << reply->rawResult().isValid(); // false, even though reply finished
                qInfo() << "Raw result fun code: " << reply->rawResult().functionCode(); // 0
                qInfo() << "Error? " << reply->errorString(); // ""
                qInfo() << "Reply data size: " << reply->rawResult().dataSize(); // 0
                qInfo() << "Reply size: " << reply->rawResult().data().size(); // 0
                QByteArray data = reply->rawResult().data(); // ""
            });
        }
    });

    return a.exec();
}

As you can see, the response I get is invalid, even though the function code is within limits (0x66), it's a part of FunctionCode enum, and it has a data size calculator.

If I change

QModbusResponse::registerDataSizeCalculator(QModbusPdu::CustomFun_ReadData ...

QModbusResponse::registerDataSizeCalculator(QModbusPdu::WriteSingleCoil ...

and make another side answer with a function code 0x05 instead of 0x66, then the response becomes valid and the data size calculator is called.

So, it seems to me, the problem is how QModbusResponse is assembled, if the function is code is custom, then it's never assigned, and therefore a default function code (invalid) stays.

Is there any way to fix the problem?