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How do I know that the client has connected to the server?

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  • N NintyS

    No, I'm not sure but when I close the program then I have a message "connected", so I thinking I connect with my server.

    Christian EhrlicherC Offline
    Christian EhrlicherC Offline
    Christian Ehrlicher
    Lifetime Qt Champion
    wrote on last edited by
    #8

    @NintyS said in How do I know that the client has connected to the server?:

    No, I'm not sure but when I close the program then I have a message "connected", so I thinking I connect with my server.

    Sorry but please be more precise. Why do you get a 'connected' when you close a program? This doesn't sounds very useful. What program is this? Please use a simple QTcpSocket as shown in the QTcpServer examples to check your program. Or try to connect with e.g. telnet to your listen port.

    Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
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    N 1 Reply Last reply
    1
    • N Offline
      N Offline
      NintyS
      wrote on last edited by
      #9

      Now this is a simple program what must connect to server and close. I will be try on my own hand, if I do it, I will write about it.

      1 Reply Last reply
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      • Christian EhrlicherC Offline
        Christian EhrlicherC Offline
        Christian Ehrlicher
        Lifetime Qt Champion
        wrote on last edited by
        #10

        This is working fine for me:

        #include <QtNetwork>
        
        int main(int argc, char* argv[])
        {
            QCoreApplication app(argc, argv);
            
            QTcpServer server;
            if (!server.listen(QHostAddress::Any, 50153))
                return 1;
            QObject::connect(&server, &QTcpServer::newConnection,
                             &server, [&server]() {
                QTcpSocket *socket = server.nextPendingConnection();
                qDebug() << "client connected from" << socket->peerAddress() << ":" << socket->peerPort();
                socket->write("Test\n");
                socket->flush();
                socket->waitForBytesWritten(300);
                socket->close();
            });
            
            QTcpSocket client;
            QObject::connect(&client, &QTcpSocket::readyRead,
                             &client, [&client]() {
                qDebug() << client.readAll();
                QCoreApplication::quit();
            });
            client.connectToHost("localhost", 50153);
            
            return app.exec();
        }
        
        

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        Visit the Qt Academy at https://academy.qt.io/catalog

        JonBJ 1 Reply Last reply
        2
        • N Offline
          N Offline
          NintyS
          wrote on last edited by
          #11

          Thank you very much :D

          1 Reply Last reply
          0
          • Christian EhrlicherC Christian Ehrlicher

            This is working fine for me:

            #include <QtNetwork>
            
            int main(int argc, char* argv[])
            {
                QCoreApplication app(argc, argv);
                
                QTcpServer server;
                if (!server.listen(QHostAddress::Any, 50153))
                    return 1;
                QObject::connect(&server, &QTcpServer::newConnection,
                                 &server, [&server]() {
                    QTcpSocket *socket = server.nextPendingConnection();
                    qDebug() << "client connected from" << socket->peerAddress() << ":" << socket->peerPort();
                    socket->write("Test\n");
                    socket->flush();
                    socket->waitForBytesWritten(300);
                    socket->close();
                });
                
                QTcpSocket client;
                QObject::connect(&client, &QTcpSocket::readyRead,
                                 &client, [&client]() {
                    qDebug() << client.readAll();
                    QCoreApplication::quit();
                });
                client.connectToHost("localhost", 50153);
                
                return app.exec();
            }
            
            
            JonBJ Offline
            JonBJ Offline
            JonB
            wrote on last edited by
            #12

            @Christian-Ehrlicher said in How do I know that the client has connected to the server?:

                socket->flush();
                socket->waitForBytesWritten(300);
            

            Does one have to have these two lines prior to socket->close(), or are you just being "safe"?

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            • Christian EhrlicherC Offline
              Christian EhrlicherC Offline
              Christian Ehrlicher
              Lifetime Qt Champion
              wrote on last edited by
              #13

              The waitForBytesWritten() is needed.

              Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
              Visit the Qt Academy at https://academy.qt.io/catalog

              KroMignonK 1 Reply Last reply
              1
              • Christian EhrlicherC Christian Ehrlicher

                @NintyS said in How do I know that the client has connected to the server?:

                No, I'm not sure but when I close the program then I have a message "connected", so I thinking I connect with my server.

                Sorry but please be more precise. Why do you get a 'connected' when you close a program? This doesn't sounds very useful. What program is this? Please use a simple QTcpSocket as shown in the QTcpServer examples to check your program. Or try to connect with e.g. telnet to your listen port.

                N Offline
                N Offline
                NintyS
                wrote on last edited by
                #14

                @Christian-Ehrlicher I know now why. I use a printf() to show the result. Now when I use qDebug I see my result after connection.

                JonBJ 1 Reply Last reply
                0
                • N NintyS

                  @Christian-Ehrlicher I know now why. I use a printf() to show the result. Now when I use qDebug I see my result after connection.

                  JonBJ Offline
                  JonBJ Offline
                  JonB
                  wrote on last edited by JonB
                  #15

                  @NintyS
                  printf() is liable to be at least line-buffered, maybe even fully buffered. You would have to follow it with fflush(stdout) to try to see the output immediately. fprintf(stderr, ...) would probably be better. In any case qDebug() is a better choice for debugging.

                  1 Reply Last reply
                  0
                  • Christian EhrlicherC Christian Ehrlicher

                    The waitForBytesWritten() is needed.

                    KroMignonK Offline
                    KroMignonK Offline
                    KroMignon
                    wrote on last edited by
                    #16

                    @Christian-Ehrlicher said in How do I know that the client has connected to the server?:

                    the waitForBytesWritten() is needed.

                    Why? My understanding was that waitForBytesWritten() is only required if not event queue is available... But without event queue, the connect() won't work.

                    It is an old maxim of mine that when you have excluded the impossible, whatever remains, however improbable, must be the truth. (Sherlock Holmes)

                    Christian EhrlicherC J.HilkJ 2 Replies Last reply
                    0
                    • KroMignonK KroMignon

                      @Christian-Ehrlicher said in How do I know that the client has connected to the server?:

                      the waitForBytesWritten() is needed.

                      Why? My understanding was that waitForBytesWritten() is only required if not event queue is available... But without event queue, the connect() won't work.

                      Christian EhrlicherC Offline
                      Christian EhrlicherC Offline
                      Christian Ehrlicher
                      Lifetime Qt Champion
                      wrote on last edited by
                      #17

                      @KroMignon Because of the close() directly afterwards. I'm pretty sure close() will call flush() before but it's not documented.

                      Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
                      Visit the Qt Academy at https://academy.qt.io/catalog

                      1 Reply Last reply
                      1
                      • KroMignonK KroMignon

                        @Christian-Ehrlicher said in How do I know that the client has connected to the server?:

                        the waitForBytesWritten() is needed.

                        Why? My understanding was that waitForBytesWritten() is only required if not event queue is available... But without event queue, the connect() won't work.

                        J.HilkJ Offline
                        J.HilkJ Offline
                        J.Hilk
                        Moderators
                        wrote on last edited by
                        #18

                        @KroMignon probably because of the immediate call to close on the socket

                        you could alternatively, potentially nest lambdas

                               QTcpSocket *socket = server.nextPendingConnection();
                                    qDebug() << "client connected from" << socket->peerAddress() << ":" << socket->peerPort();
                                    QByteArray data{"Test\n"};
                                    QObject::connect(socket, &QTcpSocket::bytesWritten, socket, [socket, bytesToSend = data.size()](qint64 bytes)->void{
                                        static qint64 bytesSend{0};
                                        bytesSend += bytes;
                                        if(static_cast<qint64>(bytesToSend) == bytesSend)
                                            socket->close();
                                    });
                                    socket->write(data);
                                });
                        

                        Be aware of the Qt Code of Conduct, when posting : https://forum.qt.io/topic/113070/qt-code-of-conduct


                        Q: What's that?
                        A: It's blue light.
                        Q: What does it do?
                        A: It turns blue.

                        KroMignonK JonBJ 2 Replies Last reply
                        1
                        • J.HilkJ J.Hilk

                          @KroMignon probably because of the immediate call to close on the socket

                          you could alternatively, potentially nest lambdas

                                 QTcpSocket *socket = server.nextPendingConnection();
                                      qDebug() << "client connected from" << socket->peerAddress() << ":" << socket->peerPort();
                                      QByteArray data{"Test\n"};
                                      QObject::connect(socket, &QTcpSocket::bytesWritten, socket, [socket, bytesToSend = data.size()](qint64 bytes)->void{
                                          static qint64 bytesSend{0};
                                          bytesSend += bytes;
                                          if(static_cast<qint64>(bytesToSend) == bytesSend)
                                              socket->close();
                                      });
                                      socket->write(data);
                                  });
                          
                          KroMignonK Offline
                          KroMignonK Offline
                          KroMignon
                          wrote on last edited by
                          #19

                          @J-Hilk said in How do I know that the client has connected to the server?:

                          you could alternatively, potentially nest lambdas

                                 QTcpSocket *socket = server.nextPendingConnection();
                                      qDebug() << "client connected from" << socket->peerAddress() << ":" << socket->peerPort();
                                      QByteArray data{"Test\n"};
                                      QObject::connect(socket, &QTcpSocket::bytesWritten, socket, [socket, bytesToSend = data.size()](qint64 bytes)->void{
                                          static qint64 bytesSend{0};
                                          bytesSend += bytes;
                                          if(static_cast<qint64>(bytesToSend) == bytesSend)
                                              socket->close();
                                      });
                                      socket->write(data);
                                  });
                          

                          Hmm, I would do it like this:

                          QTcpSocket *socket = server.nextPendingConnection();
                          qDebug() << "client connected from" << socket->peerAddress() << ":" << socket->peerPort();
                          QByteArray data{"Test\n"};
                          QObject::connect(socket, &QTcpSocket::bytesWritten, socket, [socket](qint64 bytes)->void{
                              if(socket->bytesToWrite() == 0)
                                  socket->close();
                          });
                          socket->write(data);
                          

                          It is an old maxim of mine that when you have excluded the impossible, whatever remains, however improbable, must be the truth. (Sherlock Holmes)

                          J.HilkJ 1 Reply Last reply
                          0
                          • KroMignonK KroMignon

                            @J-Hilk said in How do I know that the client has connected to the server?:

                            you could alternatively, potentially nest lambdas

                                   QTcpSocket *socket = server.nextPendingConnection();
                                        qDebug() << "client connected from" << socket->peerAddress() << ":" << socket->peerPort();
                                        QByteArray data{"Test\n"};
                                        QObject::connect(socket, &QTcpSocket::bytesWritten, socket, [socket, bytesToSend = data.size()](qint64 bytes)->void{
                                            static qint64 bytesSend{0};
                                            bytesSend += bytes;
                                            if(static_cast<qint64>(bytesToSend) == bytesSend)
                                                socket->close();
                                        });
                                        socket->write(data);
                                    });
                            

                            Hmm, I would do it like this:

                            QTcpSocket *socket = server.nextPendingConnection();
                            qDebug() << "client connected from" << socket->peerAddress() << ":" << socket->peerPort();
                            QByteArray data{"Test\n"};
                            QObject::connect(socket, &QTcpSocket::bytesWritten, socket, [socket](qint64 bytes)->void{
                                if(socket->bytesToWrite() == 0)
                                    socket->close();
                            });
                            socket->write(data);
                            
                            J.HilkJ Offline
                            J.HilkJ Offline
                            J.Hilk
                            Moderators
                            wrote on last edited by
                            #20

                            @KroMignon potentially, I'm not familiar enough with the inner workings of QAbstractSocket to say for sure, that bytesToWrite is updated before bytesWritten is emitted 🤷‍♂️


                            Be aware of the Qt Code of Conduct, when posting : https://forum.qt.io/topic/113070/qt-code-of-conduct


                            Q: What's that?
                            A: It's blue light.
                            Q: What does it do?
                            A: It turns blue.

                            1 Reply Last reply
                            0
                            • J.HilkJ J.Hilk

                              @KroMignon probably because of the immediate call to close on the socket

                              you could alternatively, potentially nest lambdas

                                     QTcpSocket *socket = server.nextPendingConnection();
                                          qDebug() << "client connected from" << socket->peerAddress() << ":" << socket->peerPort();
                                          QByteArray data{"Test\n"};
                                          QObject::connect(socket, &QTcpSocket::bytesWritten, socket, [socket, bytesToSend = data.size()](qint64 bytes)->void{
                                              static qint64 bytesSend{0};
                                              bytesSend += bytes;
                                              if(static_cast<qint64>(bytesToSend) == bytesSend)
                                                  socket->close();
                                          });
                                          socket->write(data);
                                      });
                              
                              JonBJ Offline
                              JonBJ Offline
                              JonB
                              wrote on last edited by JonB
                              #21

                              @J-Hilk said in How do I know that the client has connected to the server?:

                              static qint64 bytesSend{0};

                              You might like to come join us in my question about this over at https://forum.qt.io/topic/123582/static-in-lambda ? :)

                              1 Reply Last reply
                              0

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