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Fix problem with QTCPSocket?

  • Hello,

    I am having a bit of problem in creating a TCP client/server.
    The first message it sends, when the new connection is first established, arrives correctly to the client. However all the messages that I would like to send after are not read correctly (I think that the sending code).
    I followed the fortune examples, but I could not get it to work.
    Here's come of my code:

    @// server sending code

    void MainWindow::sendMessage()
    // what is the next pending connection, that is the socket we want to talk to
    ui->textBrowser->append("Sending message...");

    if (!ui->messageInput->text().isEmpty()) {
        // there is message in the input line
        messageToSend = ui->messageInput->text();
    } else {
        // otherwise use the predefined message
        messageToSend = "Predefined message";
    QDataStream out(&block, QIODevice::WriteOnly);
    out << (quint16)0;
    out << messageToSend;
    out << (quint16)(block.size() - sizeof(quint16));
    clientConnection->write(block);         // send the block of data
    ui->textBrowser->append("Sent: " + messageToSend);


    @// client receiving code

    QDataStream in(newSocket);
    if (blockSize == 0) {
        qDebug() << "1";
        if (newSocket->bytesAvailable() < (int)sizeof(quint16))
        in >> blockSize;
        qDebug() << blockSize << "  " << newSocket->bytesAvailable();
    if (newSocket->bytesAvailable() < blockSize) {
        qDebug() << "2";
    QString nextMessage;
    in >> nextMessage;
    qDebug() << nextMessage;


    nextMessage should be the message that was sent by the server.
    I think that the client is not reading correctly.

    Can anyone help me out?

  • Ah, sorry for repost.
    Just assume that the connection between client and server is successful.
    I am using something like this:

    In client:
    connect(newSocket, SIGNAL(readyRead()), this, SLOT(readMessage()));

    In server:
    connect(newServer, SIGNAL(newConnection()), this, SLOT(sendMessage()));

  • newConnection() "triggers" only when there are new sockets who want to connect to the sever. apparently, it is already connected so newConnection() will not be called again.

    If I remember clearly, that example follows these steps:

    client connects

    server accepts

    server sends message

    ...and server disconnects client (or client disconnects itself?)

    ..then return to step 1.

    Try disconnecting the client t the end of "sendMessage()" function.

    If your goal is to have the server only to send messages, this is OK. But if your goal is a "bidirectional" server-client connection, I don't recommend it.

  • But my thing is that I want to keep the connection open, I don't want to close it every time a message it's sent.
    Is it possible to do that?

  • [quote author="QTDavid" date="1358337004"]But my thing is that I want to keep the connection open, I don't want to close it every time a message it's sent.
    Is it possible to do that?[/quote]

    Yes, it is possible. Might be better if you have the code to revise.

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