toying around with QDataStream and QVariant serialization

receiver_main.cpp

#include <QtCore>
#include <QtNetwork>

//some custom data structure depending on QList
using DataStructure = QList<QPair<QString, QString>>;
//Q_DECLARE_METATYPE(DataStructure)

/*QDataStream& operator<<(QDataStream& stream, const DataStructure& ds) {
    stream << (quint32) ds.size();
    for(auto e : ds) stream << e;
    return stream;
}

QDataStream& operator>>(QDataStream& stream, DataStructure& ds) {
    ds.clear();
    quint32 count; stream >> count;
    ds.reserve(count);
    for(quint32 i=0; i<count; i++) {
        QPair<QString, QString> element;
        stream >> element;
        ds.push_back(std::move(element));
    }
    return stream;
}*/


int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    //qRegisterMetaType<DataStructure>("DataStructure");
    qRegisterMetaTypeStreamOperators<DataStructure>("DataStructure");

    QTcpSocket socket;
    socket.connectToHost(QHostAddress("127.0.0.1"), 9966);
    quint32 msgSize = 0;
    QObject::connect(&socket, &QTcpSocket::connected, []{ qDebug() << "connected"; });
    QObject::connect(&socket, &QTcpSocket::readyRead, [&]{
        qDebug() << "ready read";

        QDataStream in(&socket);
        in.setVersion(QDataStream::Qt_5_9);

        if(msgSize == 0) {
            if(socket.bytesAvailable() < static_cast<int>(sizeof(quint32))) return;
            in >> msgSize;
        }
        if(socket.bytesAvailable() < msgSize) return;
        QVariant variant;
        QString str;
        quint64 number;

        in >> variant;
        qDebug() << "received variant of type: " << variant.typeName();
        in >> str;
        qDebug() << str;
        in >> str;
        qDebug() << str;
        in >> number;
        qDebug() << number;
        in >> str;
        qDebug() << str;
        socket.disconnectFromHost();
        socket.close();
        qApp->quit();
    });

    return a.exec();
}

sender_main.cpp

#include <QtCore>
#include <QtNetwork>

//some custom data structure depending on QList
using DataStructure = QList<QPair<QString, QString>>;
//Q_DECLARE_METATYPE(DataStructure)

/*QDataStream& operator<<(QDataStream& stream, const DataStructure& ds) {
    stream << (quint32) ds.size();
    for(const auto& e : ds) stream << e;
    return stream;
}

QDataStream& operator>>(QDataStream& stream, DataStructure& ds) {
    ds.clear();
    quint32 count; stream >> count;
    ds.reserve(count);
    for(quint32 i=0; i<count; i++) {
        QPair<QString, QString> element;
        stream >> element;
        ds.push_back(std::move(element));
    }
    return stream;
}*/

int main(int argc, char* argv[]) {
    QCoreApplication a(argc, argv);

    //qRegisterMetaType<DataStructure>("DataStructure");
    qRegisterMetaTypeStreamOperators<DataStructure>("DataStructure");

    DataStructure dataStructure;
    //fill data structure with dummy data
    dataStructure.push_back(QPair<QString, QString>("a","aa"));
    dataStructure.push_back(QPair<QString, QString>("c","cc"));
    dataStructure.push_back(QPair<QString, QString>("b","bb"));

    QByteArray msg;
    QDataStream out(&msg, QIODevice::WriteOnly);
    out.setVersion(QDataStream::Qt_5_9);

    QVariant variant = QVariant::fromValue(dataStructure);
    qDebug() << variant.typeName() << " " << (int)variant.type();
    out << static_cast<quint32>(0);
    out << variant;
    out << QString("test");
    out << QString("another test");
    out << static_cast<quint64>(666);
    out << QString("final test");
    out.device()->seek(0); out << static_cast<quint32>(msg.size() - sizeof(quint32));

    QTcpServer server;
    QObject::connect(&server, &QTcpServer::newConnection, [&]{
        QTcpSocket* socket = server.nextPendingConnection();
        QObject::connect(socket, &QTcpSocket::bytesWritten, [socket]{
            socket->disconnectFromHost();
            socket->close();
            socket->deleteLater();
            qApp->quit();
        });
        socket->write(msg);
        socket->flush();
    });
    server.listen(QHostAddress::Any, 9966);


    return a.exec();
}