Sending messages from a client to server using network on the same machine

SGaist

First thing: you initialize your QDataStream on the wrong socket, it shall use the socket matching the connection that was established.

qcoderpro

@SGaist

Do you mean to move

in.setDevice(tcpSocket);
in.setVersion(QDataStream::Qt_4_0);

from the server's constructor into the onNewConnection slot this way, please?

void Server::onNewConnection()
{
    QTcpSocket *clientConnection = tcpServer->nextPendingConnection();
    connect(clientConnection, &QAbstractSocket::disconnected,
            clientConnection, &QObject::deleteLater);
    in.setDevice(clientConnection);
    in.setVersion(QDataStream::Qt_4_0);
    connect(clientConnection, &QAbstractSocket::readyRead, this, &Server::setMessage);
}

The error message when running the projects both at the same time: QDataStream: No transaction in progress

qcoderpro

No further help? :|

SGaist

Do you also use QDataStream to prepare the data to send ?

qcoderpro

This post is deleted!

qcoderpro

@SGaist

Yes, you're right. I partly changed all six files to match the requirements as follows:
The server part:
server.h:

class Server : public QObject
{
    Q_OBJECT
public:
    explicit Server(QObject *parent = nullptr);

public slots:
    QString initServer();
    void setMessage();
    QString getMessage() const;
    void onNewConnection();

private:
    QTcpServer* tcpServer { nullptr };
    QDataStream in;
    QString message;
};

server.cpp:

Server::Server(QObject *parent)
    : QObject{parent}
    , tcpServer(new QTcpServer(this))
{
    initServer();
    connect(tcpServer, &QTcpServer::newConnection, this, &Server::onNewConnection);
}

QString Server::initServer() {
//.. Provide the IP address and port number for the client
}

void Server::onNewConnection()
{
    QTcpSocket *clientConnection = tcpServer->nextPendingConnection();
    connect(clientConnection, &QAbstractSocket::disconnected,
            clientConnection, &QObject::deleteLater);
    in.setDevice(clientConnection);
    in.setVersion(QDataStream::Qt_4_0);
    connect(clientConnection, &QAbstractSocket::readyRead, this, &Server::setMessage);
}

void Server::setMessage()
{
    in.startTransaction();
    QString msg;
    in >> msg;

    if (!in.commitTransaction())
        message = "commitTransaction error" ;
    else
        message = msg;
}

QString Server::getMessage() const
{
    return message;
}

server's qml file:

 ColumnLayout {
        anchors.fill: parent

        Label {
            text: myObj.initServer()
        }

        Label {
            id: msgLabel
            text: myObj.getMessage()
        }
    }

    ServerClass{
        id: myObj
    }

The client part:

client.h:

class Client : public QObject
{
    Q_OBJECT

public:
    explicit Client(QObject *parent = nullptr);

public slots:
    void sendAddress(QString, QString);
    void sendMessage(const QString&);

private:
    QTcpSocket* tcpSocket { nullptr };
    QDataStream out;
};

client.cpp:

Client::Client(QObject *parent)
    : QObject{parent}
    , tcpSocket(new QTcpSocket(this))
{
    out.setDevice(tcpSocket);
    out.setVersion(QDataStream::Qt_4_0);
}

void Client::sendAddress(QString ip, QString port)
{
    tcpSocket->abort();
    tcpSocket->connectToHost(ip, port.toInt());
}

void Client::sendMessage(const QString& message)
{
    out.startTransaction();
    out << message;

    if (!out.commitTransaction())
        return ;
}

client's qml file:

 ColumnLayout {
        anchors.fill: parent

        TextField {
            id: ipAddrs
        }
        TextField {
                id: portNum
            }
        Button {
            text: "Send Address"
            onClicked: myObj.sendAddress(ipAddrs.text.toString(), portNum.text.toString())
        }

        RowLayout {
            Layout.alignment: Qt.AlignBottom

            TextField {
                id: txtField
                Layout.fillWidth: true
            }
            Button {
                text: qsTr("Send")
                onClicked: myObj.sendMessage(txtField.text)
            }
        }
    }

    ClientClass{
        id: myObj
    }
}

After running both projects this way, and typing the IP address and port number (given by the server UI) on the client UI and writing a text message there I click on the Send button, but nothing is shown on the server UI.

I'm almost sure now the goal is closer but there're still a number of mistakes that need to be worked out.

SGaist

Are you using the Fortune client and server examples as a base ?
If so, please take a look at the server side implementation, QDataStream is used there to write the data in a QByteArray that is then written in the socket. The transaction handling happens on the receiving end.

qcoderpro

@SGaist

Are you using the Fortune client and server examples as a base ?

Partly.

QDataStream is used there to write the data in a QByteArray that is then written in the socket.

I didn't know QString wouldn't work, but anyway, it's now changed to:

void Client::sendMessage(const QString& message)
{
    QByteArray block;
    QDataStream out(&block, QIODevice::WriteOnly);
    out.setVersion(QDataStream::Qt_5_10);
    out << message;
}

But still no change in the result! :|

The transaction handling happens on the receiving end.

Yes, it's implemented in the setMessage() slot.

jsulm

@qcoderpro said in Sending messages from a client to server using network on the same machine:

But still no change in the result!

Because sendMessage does not send anything.
It only writes the message into a QByteArray.
You also need to send that QByteArray through the socket.

qcoderpro

@jsulm
Yeah, right, so I added this line at the end of the slot:
tcpSocket->write(block);
But I think there's an earlier problem. No connection arrives. I set a debug in the onNewConnection() slot in the server app but nothing is printed although I put the IP and port in the client and click on the "Send Address" button! :|

jsulm

@qcoderpro Then you should debug on the client side

qcoderpro

@jsulm

The client's sendAddress slot sends the IP and port number as a string and int respectively, based on this version. So that connection is expected to be received in the server's NewConnection() slot, but it doesn't, I don't know why! :|

jsulm

@qcoderpro said in Sending messages from a client to server using network on the same machine:

sendAddress slot sends the IP and port number

It does not send anything, it just calls connectToHost. Did you check what happens on client side? Is https://doc.qt.io/qt-5/qabstractsocket.html#connected emitted? Is https://doc.qt.io/qt-5/qabstractsocket.html#errorOccurred signal emitted?

qcoderpro

@jsulm

I set this in the client's sendAddress slot:

connect(tcpSocket, &QAbstractSocket::connected, []() {
       qDebug() << "Connected to the host";
   });

And it prints that message on Application Output window. So the connection is assumed to be established correctly without errors. Right?

qcoderpro

No further contribution? :(

Bob64

@qcoderpro I'd suggest that you go back to the fortune example and debug what is happening on the client and server side until you have a good understanding. I found it very useful when I was figuring out how Qt did sockets.

Do you have any background with sockets at all? If not, I wonder if it would be worth having a play around with something like Python first to firm up the ideas. The official Python docs on sockets are very good.

qcoderpro

@Bob64
The fortune client/server apps are different from (at least) that point of view that the server sends messages to the client by a button on the client. It's way different from mine.
Well, these two QML apps are considerably simple but I don't know why we (helpers and me) can't work it out and get them to work! :(