QTcpSocket never emits readyRead when connected

KirstenS

I have been connecting to a network through an ssh command on a Linux machine:

ssh user@host.colo.edu
and then I am prompted in the terminal for a password:

mypassword
at which point, I am connected to the network. I then run netcat (a simple Unix utility that reads and writes data across network connections, using the TCP or UDP protocol) with the command:

nc -l -p 1313
where 1313 is the port number and JSON messages begin to appear in my terminal window. I would like to use Qt to have a similar result. I am open to suggestions, but I believe I need to use QTcpSocket with a QNetwork Proxy. Here is my mainwindow.cpp (I have changed the host, user, and password to something generic):

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    serverSocket = new QTcpSocket(this);
    connect(serverSocket,SIGNAL(readyRead()),this,SLOT(readyReadSlot()));
    connect(serverSocket,SIGNAL(connected()),this,SLOT(connectedSlot()));
    connect(serverSocket, SIGNAL(hostFound()),this,SLOT(hostFoundSlot()));
    connect(serverSocket,SIGNAL(error(QAbstractSocket::SocketError)),this,SLOT(errorSlot(QAbstractSocket::SocketError)));
    connect(serverSocket,SIGNAL(proxyAuthenticationRequired(QNetworkProxy,QAuthenticator*)),this,SLOT(proxyAuthenticationRequiredSlot(QNetworkProxy,QAuthenticator*)));
    connect(serverSocket,SIGNAL(stateChanged(QAbstractSocket::SocketState)),this,SLOT(stateChangedSlot(QAbstractSocket::SocketState)));
    QNetworkProxy proxy;
    proxy.setHostName("host.colo.edu");
    proxy.setPort(1313);
    proxy.setUser("user");
    proxy.setPassword("mypassword");
    serverSocket->setProxy(proxy);
    serverSocket->connectToHost("host.colo.edu",1313);
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::readyReadSlot()
{
    qDebug() << "reading...";
    while (!serverSocket->atEnd())
    {
     QByteArray data = serverSocket->read(100);
     int istop = 0;
    }
}

void MainWindow::connectedSlot()
{
    qDebug() << "connected...";
}

void MainWindow::hostFoundSlot()
{
    qDebug() << "found host...";
}

void MainWindow::errorSlot(QAbstractSocket::SocketError)
{
    qDebug() << "an error...";
}

void MainWindow::proxyAuthenticationRequiredSlot(QNetworkProxy, QAuthenticator *)
{
    qDebug() << "authentication...";
}

void MainWindow::stateChangedSlot(QAbstractSocket::SocketState socketState)
{
    qDebug() << "state changed...";
}

And here is my mainwindow.h:

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QTcpSocket>
#include <QNetworkProxy>
namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

    QTcpSocket *serverSocket;
public slots:
    void readyReadSlot();
    void connectedSlot();
    void hostFoundSlot();
    void errorSlot(QAbstractSocket::SocketError);
    void proxyAuthenticationRequiredSlot(QNetworkProxy,QAuthenticator*);
    void stateChangedSlot(QAbstractSocket::SocketState socketState);
private:
    Ui::MainWindow *ui;
};

#endif // MAINWINDOW_H

And here is the output from debug:

Debugging starts
state changed...
state changed...
found host...
state changed...
connected...
Debugging has finished
At no point do I have any errors or authentication requests, but readyRead signal never emits and readyReadSlot never gets called? Am I missing something?

[Code tags added ~kshegunov]

SGaist

Hi and welcome to devnet,

Something strange here, you seem to log through SSH and then, in your code, you are using a proxy which is not the same thing AFAIK.

KirstenS

Thanks. I want to read messages across a network connection. I was explaining how I can see the messages on Linux. I first ssh into the network and then I can run netcat , a simple Unix utility that reads and writes data across network connections, using the TCP or UDP protocol.
Based on that description, I assumed I would need a QTcpSocket. I want to use my Windows computer and my Qt application to achieve the same end. I don't think I need to ssh, but that is the method I use in Linux. What do you suggest instead?

SGaist

First you need to determine whether that machine is accessible from the outside on that port and how.

KirstenS

Thanks for explaining! Reading data across network connections is a new endeavor for me. I am confused as to what you mean by accessible to the outside on that port. I thought since I had successfully connected using that port number that would mean that it is accessible. My qdebug messages imply I have connected.

SGaist

There's one other thing that is strange, the documentation of netcat explicitly state that you should not use -p and -l together. So what exactly are you connecting to ?