QTcpServer not listening on port

dij0nmustard

Hi! I'm fairly new to QTcpServer (and qt in general) and have been following a simple tutorial to create a server. However, when I run my program in qt creator and use "netstat -a" in command prompt, I don't see the port (1234) open. I also tried using telnet 127.0.0.1 1234, and get an error saying "Connect Failed". I can ping 127.0.0.1 and get packets back successfully. Any advice? I'm unsure if there is a firewall issue or if my program is just struggling to open port 1234. Attached is my code. Any advice would be greatly appreciated!

I plan eventually to use two raspberry pi's to control motors, but that part of the code in main.cpp can be ignored.

myserver.cpp

#include <QtNetwork>
#include <QAbstractSocket>
#include "myserver.h"

myServer::myServer(QObject *parent) :
    QObject(parent)
{

    server = new QTcpServer(this);
    connect(server, &QTcpServer::newConnection, this, &myServer::newConnection);

    if(!server->listen(QHostAddress("127.0.0.1"), 1234))
    {
        qDebug() << "Server could not Start!";
    }
    else {
        qDebug() << "Server Started!";
    }
}


void myServer::newConnection()
{
    QTcpSocket *socket = server->nextPendingConnection();
    socket->write("hullo client\r\n");
    socket->flush();
    socket->waitForBytesWritten(3000);
    socket->close();
}

myserver.h

#ifndef MYSERVER_H
#define MYSERVER_H
#include <QtNetwork>
#include <QDebug>


class myServer: public QObject
{

    Q_OBJECT

public:
    explicit myServer(QObject *parent = 0); 

public slots:
    void newConnection();
    void handleReadyRead();

private:
    QTcpServer *server;

};

#endif // MYSERVER_H

main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <myserver.h>
#include <clientsocket.h>

//Define Roles here.
#define ROLE_MOTOR_CONTROLLER 1
#define ROLE_COMMAND_SENDER 2

//#define CURRENT_ROLE ROLE_COMMAND_SENDER
#define CURRENT_ROLE ROLE_MOTOR_CONTROLLER

//Use above line to change Motor Controller (server, RPI 1) or Command Sender (client, RPI 2).

int main(int argc, char *argv[])
{
#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
#endif

    QGuiApplication app(argc, argv);

    if (CURRENT_ROLE == ROLE_MOTOR_CONTROLLER) {
        // Initialize and start the server (Motor Controller)
        myServer mServer;
        // Create an instance of MotorController and start the Qt event loop
    } else if (CURRENT_ROLE == ROLE_COMMAND_SENDER) {
        // Initialize and start the socket (Command Sender)

        clientSocket mClientSocket;
        mClientSocket.Test();
        // Create an instance of CommandSender and start the Qt event loop
    }

    QQmlApplicationEngine engine;
    const QUrl url(QStringLiteral("qrc:/main.qml"));
    QObject::connect(&engine, &QQmlApplicationEngine::objectCreated,
                     &app, [url](QObject *obj, const QUrl &objUrl) {
        if (!obj && url == objUrl)
            QCoreApplication::exit(-1);
    }, Qt::QueuedConnection);
    engine.load(url);

    return app.exec();
}

SGaist

Hi and welcome to devnet,

Please re-read your main function and take into account the lifetime of the objects you create there.

dij0nmustard

@SGaist

Thanks for your answer! Can I ask you to clarify what you mean here?

When I am initializing mServer in main.cpp, is there something later on that destroys it? Do I need a while loop to maintain it?

SGaist

if (CURRENT_ROLE == ROLE_MOTOR_CONTROLLER) {
        myServer mServer;   
    } /* mServer is destroyed here*/ else {
      ... 
    }

That said, why not have real separated applications for your server and client ? You seem to try to shove everything into a single file which is a bad idea.

dij0nmustard

@SGaist

Oh I see! Thank you, that was helpful. And you bring up a great point - I'll separate them into two applications.

Thanks!