QTcpSocket in QThread

Question

I have simple server connection thread. When you call function receiveString, it fails. However when you execute same code in run(), it succeeds. What is needed for function receiveString to work?

I've tried both

bool TestServerThread::receiveString(QTcpSocket& sock, QString& str)
bool TestServerThread::receiveString(QTcpSocket* sock, QString& str)

Actual code:

TestServerThread::TestServerThread(int socketDescriptor, QObject *parent) : QThread(parent), socketDescriptor(socketDescriptor)
{
}


bool TestServerThread::receiveString(QTcpSocket& sock, QString& str)
{
    if(sock.isValid())
    {
        if(!sock.waitForReadyRead(30))
        {
            qWarning() << "fail"; // fails here
            return false;
        }
        QByteArray buf = sock.readAll();
        str = buf;
    }
}

void TestServerThread::run()
{
    QTcpSocket sock;
    if (!sock.setSocketDescriptor(socketDescriptor)) {
        emit error(sock.error());
        return;
    }

    bool ok = true;
    while(ok)
    {
        QString str;
        //if(ok) ok = receiveString(sock, str);

        if(!sock.waitForReadyRead(30))
        {
            qWarning() << "false";
        }
        QByteArray buf = sock.readAll(); // same routine succeeds
        str = buf;
        qWarning() << str;

        qWarning() << "Received: " << str;
        if(ok) ok = sendString(sock, "kaka");
    }
    sock.disconnectFromHost();
    sock.waitForDisconnected();
}

Answer 1

What is the return value or QTcpSocket::errorString()?

//...
if(!sock.waitForReadyRead(30))
{
    qWarning() << "fails " << sock.errorString(); // fails here
    emit error(sock.error());
    return false;
}
//...

Note that in the run, you are always reading the data on the socket, even if QTcpSocket::waitForReadyRead returned false.
Are you sure you don't get the same error in the run as in receiveString, but the read succeeds because you ignore this error?

Is run still succeeding if you use this code:

bool ok = true;
while(ok)
{
    QString str;
    //if(ok) ok = receiveString(sock, str);

    if(sock.waitForReadyRead(30))
    {
        QByteArray buf = sock.readAll(); // same routine succeeds
        str = buf;
        qWarning() << str;
        qWarning() << "Received: " << str;
        if(ok) 
        {
            ok = sendString(sock, "kaka");
        }
    }
    else
    {
         qWarning() << "fails " << sock.errorString();
         ok = false;
    }
}

Answer 2

either somewhere of your code ruined the process stack, or your timeout value if not enough.