Show low level Modbus packet in UI

Mark81

I know I can enable low level Modbus logging in this way:

QLoggingCategory::setFilterRules(QStringLiteral("qt.modbus* = true"));

and I can get a debug output like this:

qt.modbus: (TCP client) Connected to QHostAddress("192.168.1.157") on port 502
qt.modbus.lowlevel: (TCP client) Sent TCP ADU: "00000000000601010000000a"
qt.modbus: (TCP client) Sent TCP PDU: 0x010000000a with tId: 0
qt.modbus.lowlevel: (TCP client) Response buffer: "000000000003018101"
qt.modbus: (TCP client) tid: 0 size: 3 server address: 1
qt.modbus: (TCP client) Received PDU: 1 "01"
qt.modbus: (TCP client) Connection closed.

I'm interested to show in the UI (TextEdit) both sent and received packets: ADU and PDU.
Is there a way to retrieve them?

mrjj

Hi
you mean like
http://doc.qt.io/qt-5/qtglobal.html#qInstallMessageHandler
so all QDebug goes to your own function ?

Mark81

It might be a solution if there's no way to retrieve the raw data (the whole packets) directly from the Modbus classes. Like the sendData and reveiceData of EasyModbus.

I'll try it. Thanks.

mrjj

@Mark81
Hi
I have not used the modBus so i cant say.
Maybe Mr. @aha_1980 knows if possible.

Mark81

Following this method, I can put myMessageOutput inside my MainWindow class? Otherwise I don't understand how I can show the data in the UI.

int main(int argc, char *argv[])
{   
    QLoggingCategory::setFilterRules(QStringLiteral("qt.modbus* = true"));

    QApplication a(argc, argv);

    MainWindow w;
    qInstallMessageHandler(w.myMessageOutput);
    w.showMaximized();

    return a.exec();
}

it says:

error: reference to non-static member function must be called

but that function is not static:

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = nullptr);
    ~MainWindow();
    void myMessageOutput(QtMsgType type, const QMessageLogContext &context, const QString &msg);
}

mrjj

@Mark81
Hi
It has to a be a global function. Cannot be a member. sadly.
I used a global QObject class (pointer) as as proxy so i could emit from the global function.
Not pretty but only other alternative is a file or ifstream redirection
with cout and a custom std::streambuf child.

Mark81

Tried with no luck, surely due to lack of my knowledge:

class MessageHandler: public QObject
{
    Q_OBJECT
    MessageHandler() {}

public:
    static MessageHandler *instance()
    {
        if (!_instance) _instance = new MessageHandler;
        return _instance;
    }
    static void messageOutput(QtMsgType type, const QMessageLogContext &context, const QString &msg)
    {
        emit messageOutput_received(type, context, msg);
    }

signals:
    static void messageOutput_received(QtMsgType type, const QMessageLogContext &context, const QString &msg);

protected:
    static MessageHandler *_instance;
};

MessageHandler *MessageHandler::_instance = nullptr;

int main(int argc, char *argv[])
{   
    QLoggingCategory::setFilterRules(QStringLiteral("qt.modbus* = true"));

    QApplication a(argc, argv);
    MainWindow w;
    MessageHandler *mh = MessageHandler::instance();
    qInstallMessageHandler(&mh->messageOutput);
    QObject::connect(mh, &MessageHandler::messageOutput_received, &w, &MainWindow::myMessageOutput);
    w.showMaximized();

    return a.exec();
}

But it does't like the connect function:

error: no matching function for call to 'QObject::connect(MessageHandler*&, void ()(QtMsgType, const QMessageLogContext&, const QString&), MainWindow, void (MainWindow::*)(QtMsgType, const QMessageLogContext&, const QString&))'
QObject::connect(mh, &MessageHandler::messageOutput_received, &w, &MainWindow::myMessageOutput);
^

mrjj

Hi
The MessageHandler should not be as a singleton ( with static)
Just a small proxy that can be used to send in the global function.
MessageHandler *globalMSG; // and new it in main.cpp after QApplication
// the new function
void myMessageOutput(QtMsgType type, const QMessageLogContext &context, const QString &msg) {
...
globalMSG->emit(xxxxx)
}

Globals are not pretty so maybe someone has a more clean solution !
( i didnt find one so i used this )

aha_1980

@mrjj said in Show low level Modbus packet in UI:

Maybe Mr. @aha_1980 knows if possible.

I'm not aware of an official way to do this. qInstallMessageHandler might indeed by a solution to that.

Regards

Mark81

Got it. It works, but a native way to retrieve the raw data will be very appreciated!

aha_1980

@Mark81

Then please file a suggestion at bugreports.qt.io (and give a link to it here).