QTcpClient successfully connects, but not to my server. Where is it connecting?

Question

I have successfully built a thin client/server using Qt's Tcp Sockets API. I know it works very well, because I have sent plenty of data over the wire and verified it. However, my project manager wants a suite of unit-tests, and I'm implementing them using Qt's Test Library.

Anyhow, I'm trying to set up some dummy server to simply receive data from a QTcpSocket to verify a sendData() method in a unit test. When I connect the test socket, is shows that it is connected, but the slot for connecting the dummy server and its dummy socket is never called!

Can anyone see what I'm doing wrong here? ( I've stripped the code down down to just the parts that seem broken in the test class )

From tst_tcpcommsocket.h

#ifndef TST_TCPCOMMSOCKET_H
#define TST_TCPCOMMSOCKET_H

#include <QtCore/QString>
#include <QtTest/QtTest>

#include <iostream>

#include <QTcpSocket>
#include <QTcpServer>

class TcpCommSocketTest : public QObject
{
    Q_OBJECT

private:
    QTcpSocket* qTestSocket;
    QTcpSocket* qDummySocket;
    QTcpServer* qDummyServer;

public:
        TcpCommSocketTest();

public slots:
    void connectDummyServer();

private Q_SLOTS:
    void initTestCase();    
    void sendDataTest();    
    void cleanupTestCase();
};

#endif // TST_TCPCOMMSOCKET_H

From tst_tcpcommsocket.cpp

#include "tst_tcpcommsocket.h"

void TcpCommSocketTest::connectDummyServer()
{
    cout << "connection attempt" << endl;
    qDummySocket = qDummyServer->nextPendingConnection();
}

void TcpCommSocketTest::initTestCase()
{
    qDummySocket = NULL;
    qDummyServer = new QTcpServer();
    qDummyServer->listen( QHostAddress("127.0.0.1"), 9000 );
    connect( qDummyServer, SIGNAL(newConnection()), SLOT(connectDummyServer()) );

    qTestSocket = new QTcpSocket();
    qTestSocket->connectToHost( QHostAddress("127.0.0.1"), 9000 );

    QVERIFY( qTestSocket->waitForConnected( 5000 ) );
    QVERIFY( qTestSocket->state() == QTcpSocket::ConnectedState );
}

void TcpCommSocketTest::sendDataTest()
{
    int i=0;
    QVERIFY( qDummySocket != NULL );
}

QTEST_MAIN(TcpCommSocketTest);

The Test Run's output:

********* Start testing of TcpCommSocketTest *********
Config: Using QTest library 4.7.3, Qt 4.7.3
PASS   : TcpCommSocketTest::initTestCase()
FAIL!  : TcpCommSocketTest::sendDataTest() 'qDummySocket != NULL' returned FALSE. ()
   Loc: [-]
cleanup
PASS   : TcpCommSocketTest::cleanupTestCase()
Totals: 2 passed, 1 failed, 0 skipped

Answer 1

While QTEST_MAIN creates a QApplication and runs all your tests, it does so sequentially and not with an event loop. Therefore, while your socket can indeed connect to the server (meaning qTestSocket->waitForConnected() returns true), since the app doesn't return to an event loop, the QTcpServer's signal will not get emitted, and TcpCommSocketTest::connectDummyServer() never gets called.

Try adding a call to qApp->processEvents() at the end of initTestCase(). It should let connectDummyServer() be called.

Answer 2

You could be connecting to an instance of the server started earlier. Poke around with a process monitor to make sure you don't have any stray instances. Does your test setup automatically kick off and shutdown the dummy server? It could be that the test is succesfully starting the server, but failing to kill it.

Also, from the 127.0.0.1, the dummy server is running on the same machine as the test code right?

Answer 3

Verify the return value of qDummyServer->listen(). It should return true if the server is indeed listening at port 9000. If it returns false, chances are port 9000 is blocked by another process, and it couldn't listen. In that case, your qTestSocket connected to that other process instead of your own server.