writing to QTcpSocket does not always emit readyRead signal on opposite QTcpSocket

CybeX

I have been stuck on this for the past 5 days, I have no idea how to proceed.

Overview:

I have a client UI which interacts with a data handler library, and the data handler library utilizes a network manager library, which is where my problem lies.

More Info

Firstly, QT provides a basic example for interactions between a QTcpServer (Fortune Server)and a QTcpSocket (Fortune Client).

I thus implemented this code into an extremely basic example of my own, which works like a charm and has no issues.

My own adaption of fortune client and server for the record (basic)

Quick Explaination:

Server application runs, click on start server, then on the client side, enter text in field and click connect to server and text is displayed, easy!

Problem:

Implementing the code above into my network manager library, does not fire the QTcpSocket::readyRead() in the server application above.

It connects to the server, where the QTcpServer::newConnection() is fired, as expected, straight after which the client writes to the socket but the readyRead() on the server socket does not fire, however in the example given it does.

Note:
The same port and ip address is used in this server-client application example and my current application, and the server is also running.

Further Information:

From the above code, I copied over directly from the client. Only 2 things were changed/modified:

String that is sent to server
return types for method

This was copied into my network mannager ::write() method. When running my application, and instance of QMainWindow is passed via data handler class and creates an instance of my network manager class which inherits QObject and implements the Q_OBJECT macro.

Code Examples:

//client_UI Class (snippet):

data_mananger *dman = new data_mananger(this);                //this -> QMainWindow
ReturnObject r = dman->NET_AuthenticateUser_GetToken(Query);

//data_manager library (snippet)

data_mananger::data_mananger(QObject *_parent) :
    parent(_parent)
{}

ReturnObject data_mananger::NET_AuthenticateUser_GetToken(QString Query){
    //Query like "AUTH;U=xyz@a;P=1234"

    //convert query string to char
        QByteArray ba = Query.toLatin1();

    //send query and get QList return
        ReturnCode rCode = networkManager.write(ba);

    //...
}

//netman library (snippet)

//.h

class NETMANSHARED_EXPORT netman : public QObject
{
    Q_OBJECT
public
    netman();
    netman(QObject *_parent);
    //...

private:
    QTcpSocket *tcp_con;
    //...
};

//cpp

netman::netman(QObject *_parent) :
    parent(_parent)
{
    tcp_con = new QTcpSocket(parent);
}

        return;
    }
    serverIP.setAddress(serverInfo.addresses().first().toIPv4Address());
}

ReturnCode netman::write(QByteArray message, int portNumber){

    tcp_con->connectToHost(QHostAddress("127.0.0.1"), 5000);

    if (!tcp_con->waitForConnected())
    {
        qDebug(log_lib_netman_err) << "Unable to connect to server";
        return ReturnCode::FailedConnecting;
    }

    if (!tcp_con->isValid()) {
        qDebug(log_lib_netman_err) << "tcp socket invalid";
        return ReturnCode::SocketError;
    }

    if (!tcp_con->isOpen()) {
        qDebug(log_lib_netman_err) << "tcp socket not open";
        return ReturnCode::SocketError;
    }

    //    QByteArray block(message);
    QByteArray block;
    QDataStream out(&block,QIODevice::WriteOnly);
    out.setVersion(QDataStream::Qt_4_0);

    out << QString("Hello world");

    if (!tcp_con->write(block)){
        qDebug(log_lib_netman_err) << "Unable to send data to server";
        return ReturnCode::WriteFailed;
    }
    else{
        qDebug(log_lib_netman_info) << "Data block sent";
        return ReturnCode::SentSuccess;
    }
}

Conclusion:

The core code of the client side has been fully implemented, yet I cannot see why this error occurs.

I would very much appreciate help/advice!

SGaist

Hi,

Did you check that you are not sending an empty QByteArray ?

kshegunov

Isn't this the same issue as here https://forum.qt.io/topic/75821/qabstractsocket-unknownsocketerror-provides-errorstring-of-unknownerror?

Unsolved writing to QTcpSocket does not always emit readyRead signal on opposite QTcpSocket