Qt QTcpSocket never connects

[Colton]

I use a QTcpSocket to periodically receive data (every second roughly). It works great normally, but on iOS 13 Pro Max, if the user switches from wifi to cellular, the socket disconnects and will not reconnect if the socket is recreated. The socket needs to be recreated manually by the user at a later point. If they instead switch from cell to wifi, it works fine.

std::shared_ptr<NTRIPAPI::NTRIPReadState> NTRIPAPI::NTRIPConnection::NTRIPGet(NTRIPAPI::NTRIPRequest req)
{
    auto readState = std::make_shared<NTRIPReadState>();
    auto startTimer = new QTimer(this);
    auto connectTimer = new QTimer(this);
    QByteArray msg = req.ConstructRequest(m_settings);
    auto reconnect = [readState, req, connectTimer]
    {
        readState->in = NTRIPReadState::IN_START;
        // Time increases by square root to prevent overloading the NTRIP caster (no more than 5 minutes).
        connectTimer->setInterval(fmin(pow(connectTimer->interval()/1000.0, 2.0), 300.0)*1000.0);
        connectTimer->start();
    };
    auto addSocket = [=]
    {
        readState->socket = req.createSocket(); // return new QTcpSocket();
        connect(readState->socket, &QAbstractSocket::connected, this, [readState, msg]
        {
            qsizetype size = msg.size();
            qint64 cursor = 0;
            qint64 written;
            qDebug() << "Connected, writing request";
            do
            {
                written = readState->socket->write(msg.mid(cursor));
                cursor += written;
            }
            while (cursor < size && readState->socket->isWritable());
        });
        connect(readState->socket, &QAbstractSocket::readyRead, this, []
        {
            // ...
        });
        connect(readState->socket, &QAbstractSocket::disconnected, this, [this, readState, req, startTimer, connectTimer]
        {
            // ...
        });
        connect(readState->socket, &QAbstractSocket::errorOccurred, this, [this, readState, req, startTimer, reconnect](QAbstractSocket::SocketError socketError)
        {
            bool isRecoverable = true;
            if (startTimer->isActive())
                startTimer->stop();
            // ...
            if (isRecoverable) {
                if (!readState->socket->isValid())
                {
                    readState->socket->deleteLater();
                    readState->socket = nullptr;
                }
                reconnect();
            } else {
                readState->NTRIPDisconnect(); // socket->disconnectFromHost();
            }
        });
    };
    // Setup the start timer.
    startTimer->setSingleShot(true);
    startTimer->setInterval(10000); // 10 s
    startTimer->callOnTimeout([this, readState, req, reconnect]
    {
        // Timeout occurred
        reconnect();
    });
    // Create the socket
    addSocket();
    // Setup the connect timer to connect on the next frame
    connectTimer->setSingleShot(true);
    connectTimer->callOnTimeout([this, readState, startTimer, addSocket]
    {
        // todo: If the socket is invalid, delete it, recreate the socket
        if (readState->in == NTRIPReadState::IN_START)
        {
            if (readState->socket == nullptr)
            {
                qDebug() << "Recreating the socket";
                addSocket();
            }
            startTimer->start();
            qDebug() << "Calling connectToHost";
            readState->socket->connectToHost(m_settings->hostname(), m_settings->port());
        }
        else
            qDebug() << "Ignoring connect request for invalid NTRIP GET request";
    });
    // Send the request
    connectTimer->start(0);
    connectTimer->setInterval(2000);
    return readState;
}

This is a limited version of that connection code. Am I doing something wrong here? Or, is this an iOS bug (I believe Qt uses an NSStream) that I should report to Apple?

[SGaist]

Hi,

I have not checked the iOS implementation lately but I am wondering whether you are hitting what is described here.

[Colton]

Perhaps. I'm not sure how I would test for that (without recompiling Qt, which does not work on my machine)

[SGaist]

I would check the socket implementation for iOS to get started.