Sending Data from Client to Server

star673 · 12 May 2022, 15:00

Hello all,

I am trying to amke sever and client connection whiche enables to send data to both directions. It is a little demo that I am trying to understand the structure. I will send data from server to client but I cant send data from client to server. I have created two different console applications like ServerConsole and ClientConsole.

My server.cpp file is below.

#include "server.h"

Server::Server()
{
    tcpServer = new QTcpServer();
     connect(tcpServer,&QTcpServer::newConnection,this,&Server::newConnection);
     initServer();
}

void Server::incomingConnection(int socketfd){
    QTcpSocket *client=new QTcpSocket(this);
//    client->setSocketDescriptor(socketfd);
//    clients.insert(client);

    qDebug() << "New client from: " << client->peerAddress().toString();

    connect(client,SIGNAL(readyRead()),this,SLOT(readyRead()));
    connect(client,SIGNAL(disconnected()),this,SLOT(disconnected()));
}

void Server::newConnection(){
    qDebug() << "-------NEW CONNECTION SLOT--------";
    clientConnection = tcpServer->nextPendingConnection();
     connect(clientConnection, &QAbstractSocket::disconnected,
             clientConnection, &QObject::deleteLater);


     clientConnection->write("ABCDE");
     //clientConnection->disconnectFromHost();
}


void Server::readyRead(){
   qDebug() << "|||||||||||READYREAD SLOT--------";
    qDebug() << clientConnection->readAll();
}

void Server::disconnected(){
    qDebug() << "//////////DISCONNECTED CONNECTION SLOT--------";
}

void Server::initServer(){

if (!tcpServer->listen(QHostAddress::Any,45442)) {
    qDebug() << tcpServer->errorString();

}
}

My server.h file is below.

#ifndef SERVER_H
#define SERVER_H


#include <QObject>
#include <QTcpServer>
#include <QTcpSocket>
#include <QDebug>
#include <QDataStream>
#include <QByteArray>
#include <QNetworkInterface>
#include <QAbstractSocket>

class Server : public QTcpServer
{
public:
    Server();
    QTcpServer *tcpServer = nullptr;
    void initServer();
    QTcpSocket *clientConnection;





protected:
    void incomingConnection(int socketfd);

public slots:
    void newConnection();
    void readyRead();
    void disconnected();
private:
    QSet<QTcpSocket*> clients;
};

#endif // SERVER_H

My main.cpp file for Server application is below.

#include <QCoreApplication>
#include "server.h"

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    Server server;

    return a.exec();
}

My client.cpp is below.

#include "client.h"

Client::Client()
{
    tcpSocket = new QTcpSocket();
    tcpSocket->connectToHost(QHostAddress::Any,45442);
    connect(tcpSocket,SIGNAL(error(QAbstractSocket::SocketError)),this,SLOT(displayError(QAbstractSocket::SocketError)));
    connect(tcpSocket, &QTcpSocket::connected, this, &Client::sendMessageToServer);
    connect(tcpSocket,&QTcpSocket::readyRead, this, &Client::readyRead);

}

void Client::displayError(QAbstractSocket::SocketError socketError){

    switch(socketError){
    case QAbstractSocket::RemoteHostClosedError:
        break;

    case QAbstractSocket::HostNotFoundError:
        qDebug() << "HostNotFoundError. Connection was refused. Server is not working";
        break;


    case QAbstractSocket::ConnectionRefusedError:
        qDebug() << "ConnectionRefusedError. Client. The host was not found";
        break;

    default:
        qDebug() << "ErrorString : " << tcpSocket->errorString();
  }

}

void Client::sendMessageToServer(){
    qDebug() << "INSIDe sendMessageToServer";
    tcpSocket->write("MessageFromClient");
    tcpSocket->flush();

}

void Client::readyRead(){
    qDebug() << "///READYREAD SLOT///";
    qDebug() << tcpSocket->readAll();


}

My client.h is below.

#ifndef CLIENT_H
#define CLIENT_H

#include <QObject>
#include <QTcpServer>
#include <QTcpSocket>
#include <QDebug>
#include <QDataStream>
#include <QByteArray>
#include <QNetworkInterface>
#include <QAbstractSocket>

class Client  : public QTcpSocket
{
public:
    Client();
    QTcpSocket *tcpSocket = nullptr;

public slots:
    void displayError(QAbstractSocket::SocketError socketError);
    void sendMessageToServer();
    void readyRead();
};

#endif // CLIENT_H

My main.cpp file for Client application is below.

#include <QCoreApplication>
#include "client.h"

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    Client client;

    return a.exec();
}

I would like to send the data without disconnected from client or server. How can I sending data to both directions? Any help will be appreciated.

jsulm · 17 May 2022, 10:23

@star673 said in Sending Data from Client to Server:

void Server::incomingConnection(int socketfd){

If you check the documentation you will see that incomingConnection is a protected virtual method in QTcpServer. If you want to use it you have to subclass QTcpServer and override it. But if you use QTcpServer::newConnection signal there is no need for incomingConnection - simply move the code from your incomingConnection to newConnection.

JonB · 13 May 2022, 05:36

@star673
@ELIF in thread https://forum.qt.io/topic/136412/client-to-server-message-sending seems to be trying to do the same thing as you? You two should co-operate!

I admit I have not tried/tested anything in this area, but what exactly is the problem? So far as I know sockets are open read/write, so in principle either side can just read from/write to their end of the socket and the reverse at the other side and it should just "work"? Unless someone says I am mistaken....

star673 · 13 May 2022, 05:44

@JonB
Unfortubately, I cant send data from client to server. Can you have a chance to execute the applications that I send it?
It shouldn't be any problem as I know like you said. There might be a socket problem in my case but I could not get it exactly.

jsulm · 13 May 2022, 08:29

@star673 But what exactly does not work?
Can your client connect to the server?
Do you see incoming connection on the server?

ELIF · 13 May 2022, 05:53

Yes we see incoming connection on server side.There is a successful connection.

But we can not see the message on server ui . We should see the message on server part

jsulm · E ELIF 13 May 2022, 05:47

@ELIF Your server code is wrong. You need to connect a slot to readyRead signal from clientConnection! clientConnection is the socket to communicate with the client. QTcpServer has no readyRead signal (it would not make sense to have it as QTcpServer can manage many connections at the same time).

ELIF · 13 May 2022, 06:39

@jsulm said in Sending Data from Client to Server:

Your server code is wrong

Which one ? would yo show wrong codes ?
I understand somehow.

Thank you.

KroMignon · E ELIF 13 May 2022, 06:28

@ELIF said in Sending Data from Client to Server:

Which one ? would yo show wrong codes ?

There are many errors on it:

first, why do you sub-classing QTcpServer and not QObject ?
second, to be able to define signals/slots you must add Q_OBJECT in you class header

jsulm · E ELIF 13 May 2022, 06:28

@ELIF said in Sending Data from Client to Server:

Which one ? would yo show wrong codes ?

I already said what is wrong: "You need to connect a slot to readyRead signal from clientConnection!"
Also comment from @KroMignon is correct: it makes no sense to subclass QTcpServer and then add a QTcpServer member variable...

star673 · 13 May 2022, 09:09

I got an output in server side is like:
-------NEW CONNECTION SLOT--------
Press <RETURN> to close this window...

Inclient side is the oput like:
QObject::connect: No such slot QTcpSocket::displayError(QAbstractSocket::SocketError) in ../ClientConsole/client.cpp:7
INSIDe sendMessageToServer

I have changed the server.cpp is like below. Like you said, I have used clientConnection object for readyRead slot. The connection has accomplished but I couldnt get the data.

#include "server.h"

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

void Server::incomingConnection(int socketfd){
    clientConnection=new QTcpSocket(this);
    clientConnection = tcpServer->nextPendingConnection();
     connect(clientConnection, &QAbstractSocket::disconnected,
             clientConnection, &QObject::deleteLater);
//    client->setSocketDescriptor(socketfd);
//    clients.insert(client);

    qDebug() << "New client from: " << clientConnection->peerAddress().toString();

    connect(clientConnection,SIGNAL(readyRead()),this,SLOT(readyRead()));
    connect(clientConnection,SIGNAL(disconnected()),this,SLOT(disconnected()));
}

void Server::newConnection(){
    qDebug() << "-------NEW CONNECTION SLOT--------";



     clientConnection->write("ABCDE");
     //clientConnection->disconnectFromHost();
}


void Server::readyRead(){
   qDebug() << "|||||||||||READYREAD SLOT--------";
    qDebug() << clientConnection->readAll();
}

void Server::disconnected(){
    qDebug() << "//////////DISCONNECTED CONNECTION SLOT--------";
}

void Server::initServer(){

if (!tcpServer->listen(QHostAddress::Any,45442)) {
    qDebug() << "AAAA";
    qDebug() << tcpServer->errorString();

}
}

JonB · 13 May 2022, 09:33

@star673 said in Sending Data from Client to Server:

clientConnection=new QTcpSocket(this);
clientConnection = tcpServer->nextPendingConnection();

Why do you have that first line here? All it does is leak a new QTcpSocket.

The connection has accomplished but I couldnt get the data.

Is your Server::readyRead() called at all?

Inclient side is the oput like:
QObject::connect: No such slot QTcpSocket::displayError(QAbstractSocket::SocketError) in ../ClientConsole/client.cpp:7
INSIDe sendMessageToServer

Then you have an error in client.cpp, which has nothing to do with the server code you are showing....

connect(tcpSocket,SIGNAL(error(QAbstractSocket::SocketError)),this,SLOT(displayError(QAbstractSocket::SocketError)));
connect(tcpSocket, &QTcpSocket::connected, this, &Client::sendMessageToServer);

You would not get runtime errors if you made all your connections use the new style connect syntax, like the second line here. Get rid of all your SIGNAL/SLOT() macro connections, everywhere, and see where you are.

Press <RETURN> to close this window...

This looks like the server program has exited? Use a debugger/debug statements to trace what is happening in the server.

star673 · J JonB 13 May 2022, 09:09

@JonB
I have commented this line.

clientConnection=new QTcpSocket(this);

When I commented the connect functions server application did not crashed. It seems the problem is related with these lines. Did I use them worng?

    connect(clientConnection,SIGNAL(readyRead()),this,SLOT(readyRead()));
    connect(clientConnection,SIGNAL(disconnected()),this,SLOT(disconnected()));

JonB · 13 May 2022, 21:19

@star673

@JonB said in Sending Data from Client to Server:

Get rid of all your SIGNAL/SLOT() macro connections, everywhere, and see where you are.

Come back when you have done that....

[I can see one thing which looks wrong at both your client & server sides, let's see whether it gets picked up. In any case, and especially with the trouble you are having, you really do need to change over to new style connects for all your code.]

hix_boz · J JonB 13 May 2022, 09:35

This post is deleted!

star673 · 13 May 2022, 22:53

@JonB

How to change this line?

connect(tcpSocket,SIGNAL(error(QAbstractSocket::SocketError)),this,SLOT(displayError(QAbstractSocket::SocketError)));

JonB · wrote on 13 May 2022, 22:53

@star673

connect(tcpSocket, &QTcpSocket::error, this, &ThisClass::displayError);

UPDATE
As per @Christian-Ehrlicher's link below, the QTcpSocket::error signal is overloaded in this class and you will actually need the QOverload<QAbstractSocket::SocketError>::of() shown there. You will also note that this method is now obsolete and you are advised to "Use errorOccurred() instead", which will look simpler.

Christian Ehrlicher · wrote on 14 May 2022, 07:28

@star673 said in Sending Data from Client to Server:

How to change this line?

By looking into the documentation... reading seems to be very hard.

star673 · J JonB 13 May 2022, 09:09

@JonB

I hav changed the error slot like below.

    connect(tcpSocket, QOverload<QAbstractSocket::SocketError>::of(&QAbstractSocket::error),
        [=](QAbstractSocket::SocketError socketError){

        switch(socketError){
        case QAbstractSocket::RemoteHostClosedError:
            break;

        case QAbstractSocket::HostNotFoundError:
            qDebug() << "HostNotFoundError. Connection was refused. Server is not working";
            break;


        case QAbstractSocket::ConnectionRefusedError:
            qDebug() << "ConnectionRefusedError. Client. The host was not found";
            break;

        default:
            qDebug() << "ErrorString : " << tcpSocket->errorString();
      }


    });

Now I dont have any runtime error like before. The connected signal is emitted by the client but than nothing happens. I could not read from client, too. There is no printed socket error. My incoming connection function like below.

void Server::incomingConnection(int socketfd){
   // clientConnection=new QTcpSocket(this);
    clientConnection = tcpServer->nextPendingConnection();
     connect(clientConnection, &QAbstractSocket::disconnected,
             clientConnection, &QObject::deleteLater);

//    client->setSocketDescriptor(socketfd);
//    clients.insert(client);

    qDebug() << "New client from: " << clientConnection->peerAddress().toString();

There is no print which starting "New client from" so it seems something wron with server side.

Christian Ehrlicher · 16 May 2022, 18:48

Please show your actual code with the new signal/slot syntax.

star673 · 17 May 2022, 05:38

@Christian-Ehrlicher

My server.cpp file is,

#include "server.h"

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

void Server::incomingConnection(int socketfd){
   // clientConnection=new QTcpSocket(this);
    clientConnection = tcpServer->nextPendingConnection();
     connect(clientConnection, &QAbstractSocket::disconnected,
             clientConnection, &QObject::deleteLater);

//    client->setSocketDescriptor(socketfd);
//    clients.insert(client);

    qDebug() << "New client from: " << clientConnection->peerAddress().toString();

    connect(clientConnection,SIGNAL(readyRead()),this,SLOT(readyRead()));
    connect(clientConnection,SIGNAL(disconnected()),this,SLOT(disconnected()));
}

void Server::newConnection(){
    qDebug() << "-------NEW CONNECTION SLOT--------";

//    QByteArray block;
//    QDataStream out(&block, QIODevice::ReadWrite);
//    out.setVersion(QDataStream::Qt_5_9);

//    out << "ABCderfHt";


     clientConnection->write("ABCDE");
     //clientConnection->disconnectFromHost();
}


void Server::readyRead(){
   qDebug() << "|||||||||||READYREAD SLOT--------";



    qDebug() << clientConnection->readAll();
}

void Server::disconnected(){
    qDebug() << "//////////DISCONNECTED CONNECTION SLOT--------";
}

void Server::initServer(){

    if (!tcpServer->listen(QHostAddress::Any,45442)) {
        qDebug() << tcpServer->errorString();

    }

    else{
        qDebug() << "Listening";
    }
}

My server.h file is,

#ifndef SERVER_H
#define SERVER_H


#include <QObject>
#include <QTcpServer>
#include <QTcpSocket>
#include <QDebug>
#include <QDataStream>
#include <QByteArray>
#include <QNetworkInterface>
#include <QAbstractSocket>





class Server : public QObject
{

    Q_OBJECT

public:
    explicit Server(QObject *parent = nullptr);
    QTcpServer *tcpServer = nullptr;
    void initServer();
    QTcpSocket *clientConnection;
   // QDataStream out;





protected:
    void incomingConnection(int socketfd);

public slots:
    void newConnection();
    void readyRead();
    void disconnected();
private:
    QSet<QTcpSocket*> clients;
};

#endif // SERVER_H

The main.cpp on the server side,

#include <QCoreApplication>
#include "server.h"

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    Server server;

    return a.exec();
}

My client.cpp is,

#include "client.h"

Client::Client()
{
    tcpSocket = new QTcpSocket();
    tcpSocket->connectToHost(QHostAddress::LocalHost,45442);
    //connect(tcpSocket,SIGNAL(error(QAbstractSocket::SocketError)),this,SLOT(displayError(QAbstractSocket::SocketError)));
   // connect(tcpSocket,QOverload<QAbstractSocket::SocketError>::of(error),this,&Client::displayError);
    connect(tcpSocket, QOverload<QAbstractSocket::SocketError>::of(&QAbstractSocket::error),
        [=](QAbstractSocket::SocketError socketError){

        switch(socketError){
        case QAbstractSocket::RemoteHostClosedError:
            break;

        case QAbstractSocket::HostNotFoundError:
            qDebug() << "HostNotFoundError. Connection was refused. Server is not working";
            break;


        case QAbstractSocket::ConnectionRefusedError:
            qDebug() << "ConnectionRefusedError. Client. The host was not found";
            break;

        default:
            qDebug() << "ErrorString : " << tcpSocket->errorString();
      }


    });


    connect(tcpSocket, &QTcpSocket::connected, this, &Client::sendMessageToServer);
    connect(tcpSocket,&QTcpSocket::readyRead, this, &Client::readyRead);

}

void Client::displayError(QAbstractSocket::SocketError socketError){

    switch(socketError){
    case QAbstractSocket::RemoteHostClosedError:
        break;

    case QAbstractSocket::HostNotFoundError:
        qDebug() << "HostNotFoundError. Connection was refused. Server is not working";
        break;


    case QAbstractSocket::ConnectionRefusedError:
        qDebug() << "ConnectionRefusedError. Client. The host was not found";
        break;

    default:
        qDebug() << "ErrorString : " << tcpSocket->errorString();
  }

}

void Client::sendMessageToServer(){
    qDebug() << "INSIDe sendMessageToServer";
    //tcpSocket->waitForReadyRead();
    qDebug() << tcpSocket->canReadLine() << tcpSocket->readAll();
    tcpSocket->write("MessageFromClient");
    //tcpSocket->flush();

}

void Client::readyRead(){
    qDebug() << "///READYREAD SLOT///";

//    in.startTransaction();

//    QString nextFortune;
//    in >> nextFortune;

//    if (!in.commitTransaction())
//        return;
    qDebug() << tcpSocket->readAll();


}

My client.h is,

#ifndef CLIENT_H
#define CLIENT_H

#include <QObject>
#include <QTcpServer>
#include <QTcpSocket>
#include <QDebug>
#include <QDataStream>
#include <QByteArray>
#include <QNetworkInterface>
#include <QAbstractSocket>

class Client  : public QTcpSocket
{
public:
    Client();
    QTcpSocket *tcpSocket = nullptr;
     QDataStream in;

public slots:
    void displayError(QAbstractSocket::SocketError socketError);
    void sendMessageToServer();
    void readyRead();
};

#endif // CLIENT_H

The main.cpp on the client side is,

#include <QCoreApplication>
#include "client.h"

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    Client client;

    return a.exec();
}