TCP client and QThread facing issue

[ManiRon]

I am trying to send the data from the QThread through QTCPSocket . I connect to server from main window and get a data from the user and when the user presses the sen botton i start the thread and inside the run() i have called another function that transmits the user entered data . But the problem is it is not transmitting .
(Note: both the functions are inside a QThread)

inside run()
          {
              SendData(data);
           }


sendData(Qstring str)
 {
  QTcpSocket tcpSocket;

    QByteArray arrBlock;
    QDataStream out(&arrBlock, QIODevice::WriteOnly);
    //out.setVersion(QDataStream::Qt_5_10);
    out << quint16(0) << str;

    out.device()->seek(0);
    out << quint16(arrBlock.size() - sizeof(quint16));
   qDebug("%s",str.toLatin1().data());

    tcpSocket.write(arrBlock);
 }

[jsulm]

@ManiRon said in TCP client and QThread facing issue:

QTcpSocket tcpSocket;

Where do you connect this socket?!
In this piece of code you don't - how can it work?

[JKSH]

@ManiRon said in TCP client and QThread facing issue:

I am trying to send the data from the QThread through QTCPSocket .

First, I suggest you try to send the data from your main thread. After that, decide if you need a thread or not.

Anyway, @jsulm has identified your main problem: You haven't told your QTcpSocket where to transmit the data.

See the examples to get started:

• https://doc.qt.io/qt-5/qtnetwork-fortuneclient-example.html
• https://doc.qt.io/qt-5/qtnetwork-fortuneserver-example.html

[ManiRon]

@jsulm

void MainWindow::on_pushButton_connect_clicked()
{
client->connect2host();
}

[jsulm]

@ManiRon This tcpSocket is a LOCAL variable and for sure not what you call in on_pushButton_connect_clicked():

sendData(Qstring str)
 {
  QTcpSocket tcpSocket; // This is a LOCAL variable!

And I really don't get it: I asked about "tcpSocket" and you're writing something about "client"?

Also it is called connectToHost not connect2Host.

[ManiRon]

@jsulm

MyThread.cpp

                 TestThread::TestThread()
                 {

                  }

            void TestThread :: run()
             {
   
                qDebug("%s",s.toLatin1().data());
               sendData(s);
               }
           void TestThread :: sendData(QString str)
            {
           QByteArray arrBlock;
        QDataStream out(&arrBlock, QIODevice::WriteOnly);
        //out.setVersion(QDataStream::Qt_5_10);
        out << quint16(0) << str;

        out.device()->seek(0);
        out << quint16(arrBlock.size() - sizeof(quint16));
           qDebug("%s",str.toLatin1().data());

        tcpSocket1->write(arrBlock);

       }

Myclient.cpp

ClientStuff::ClientStuff(
        const QString hostAddress,
        int portNumber,
        QObject *parent
        ) : QObject(parent), m_nNextBlockSize(0)
{
    status = false;

    host = hostAddress;
    port = portNumber;

    tcpSocket = new QTcpSocket(this);
    connect(tcpSocket, &QTcpSocket::disconnected, this, &ClientStuff::closeConnection);

    timeoutTimer = new QTimer();
    timeoutTimer->setSingleShot(true);
    connect(timeoutTimer, &QTimer::timeout, this, &ClientStuff::connectionTimeout);
}

void ClientStuff::connect2host()
{
    timeoutTimer->start(3000);

    tcpSocket->connectToHost(host, port);
    connect(tcpSocket, &QTcpSocket::connected, this, &ClientStuff::connected);
    connect(tcpSocket, &QTcpSocket::readyRead, this, &ClientStuff::readyRead);
}

void ClientStuff::connectionTimeout()
{
    //qDebug() << tcpSocket->state();
    if(tcpSocket->state() == QAbstractSocket::ConnectingState)
    {
        tcpSocket->abort();
        emit tcpSocket->error(QAbstractSocket::SocketTimeoutError);
    }
}

void ClientStuff::connected()
{
    status = true;
    emit statusChanged(status);
}

bool ClientStuff::getStatus() {return status;}

void ClientStuff::readyRead()
{
    QDataStream in(tcpSocket);
    for (;;)
    {
        if (!m_nNextBlockSize)
        {
            if (tcpSocket->bytesAvailable() < sizeof(quint16)) { break; }
            in >> m_nNextBlockSize;
        }

        if (tcpSocket->bytesAvailable() < m_nNextBlockSize) { break; }

        QString str; in >> str;

        if (str == "0")
        {
            str = "Connection closed";
            closeConnection();
        }

        emit hasReadSome(str);
        m_nNextBlockSize = 0;
    }
}



void ClientStuff::closeConnection()
{
    timeoutTimer->stop();

    //qDebug() << tcpSocket->state();
    disconnect(tcpSocket, &QTcpSocket::connected, 0, 0);
    disconnect(tcpSocket, &QTcpSocket::readyRead, 0, 0);

    bool shouldEmit = false;
    switch (tcpSocket->state())
    {
        case 0:
            tcpSocket->disconnectFromHost();
            shouldEmit = true;
            break;
        case 2:
            tcpSocket->abort();
            shouldEmit = true;
            break;
        default:
            tcpSocket->abort();
    }

    if (shouldEmit)
    {
        status = false;
        emit statusChanged(status);
    }
}

MainWindow.cpp

MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent), ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    ui->pushButton_disconnect->setVisible(false);

    client = new ClientStuff("localhost", 6547);

    setStatus(client->getStatus());

    set = new TestThread ;

    connect(client, &ClientStuff::hasReadSome, this, &MainWindow::receivedSomething);
    connect(client, &ClientStuff::statusChanged, this, &MainWindow::setStatus);
    // FIXME change this connection to the new syntax
    connect(tcpSocket, SIGNAL(error(QAbstractSocket::SocketError)),
            this, SLOT(gotError(QAbstractSocket::SocketError)));
}

MainWindow::~MainWindow()
{
    delete client;
    delete ui;
}

void MainWindow::setStatus(bool newStatus)
{
    if(newStatus)
    {
        ui->label_status->setText(
                    tr("<font color=\"green\">CONNECTED</font>"));
        ui->pushButton_connect->setVisible(false);
        ui->pushButton_disconnect->setVisible(true);
    }
    else
    {
        ui->label_status->setText(
                tr("<font color=\"red\">DISCONNECTED</font>"));
        ui->pushButton_connect->setVisible(true);
        ui->pushButton_disconnect->setVisible(false);
    }
}

void MainWindow::receivedSomething(QString msg)
{
    ui->textEdit_log->append(msg);
}

void MainWindow::gotError(QAbstractSocket::SocketError err)
{
    //qDebug() << "got error";
    QString strError = "unknown";
    switch (err)
    {
        case 0:
            strError = "Connection was refused";
            break;
        case 1:
            strError = "Remote host closed the connection";
            break;
        case 2:
            strError = "Host address was not found";
            break;
        case 5:
            strError = "Connection timed out";
            break;
        default:
            strError = "Unknown error";
    }

    ui->textEdit_log->append(strError);
}

void MainWindow::on_pushButton_connect_clicked()
{
    client->connect2host();
}

void MainWindow::on_pushButton_send_clicked()
{





    set->s = ui->lineEdit_message->text();
    
    set->start();
    

}

void MainWindow::on_pushButton_disconnect_clicked()
{
    client->closeConnection();
}

[J.Hilk]

@ManiRon
oh dear,
this is a mess!
You have 3 different QTcpSockets instances in 3 classes.
And on top of that your QThread approach is at the very least unflattering.

I would suggest, make your very own capsuled tcp-communication class with one instance of QTcpSocket -object.
Make sure it works and than think if you really need a thread for it or not. If you want/need one, you can very simply move your communication class to that thread.

[kshegunov]

My advice: read first, it's more important and bears fruit in the long run, code later.

@J.Hilk said in TCP client and QThread facing issue:

I would suggest, make your very own capsuled tcp-communication class with one instance of QTcpSocket -object.

Like it's done here.

[ManiRon]

@J.Hilk @kshegunov

I am looking for sample program for client. In which client is connected from one thread and transmission and receiving of data through same client from another thread. is there any sample , if yes kindly share the link .

[VRonin]

@ManiRon said in TCP client and QThread facing issue:

if yes kindly share the link .

@kshegunov said in TCP client and QThread facing issue:

Like it's done here.