[SOLVED] Network Problems (QTcpSocket, QTcpServer)

[karl_qt]

Hello,
I have two applications, a server and a client. Both run under Windos 8.1 x64. The server uses a class called worker, which is derived from QTcpServer:

private:
	QSet<QTcpSocket *> clients;

Worker::Worker( QObject * parent )
	: QTcpServer( parent )
{
}

Worker::~Worker( void )
{
}

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

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

void Worker::readClient( void )
{
	QTcpSocket * client = (QTcpSocket *)sender();

	list<string> parameter;
	while( client->canReadLine() ) 
	{
		string line_received( client->readLine().data() );
		parameter.push_back( line_received );
	}

    // do something with parameter and create result

	list<string>::iterator it;
	for( it = result.begin(); it != result.end(); ++it )
	{
		client->write( QByteArray( it->c_str() ) );
	}
}

void Worker::discardClient( void )
{
	QTcpSocket * client = (QTcpSocket *)sender();
	clients.remove( client );
}

The Server starts listing by:

	worker = new Worker( app );
	if( !worker->listen( QHostAddress::Any, port ) || worker->hasError() )
	{
		// An error occured
		return;
	}

The client uses an instance of QTcpSocket to connect to the server:

	socket = new QTcpSocket( this );

	socket->connectToHost( ip_address, ip_port );
	if( socket->waitForConnected() )
	{
		socket->write( QByteArray( ... ) );
	}
	else
	{
		// error: probably connection not possible
		return;
	}

	if( !socket->waitForReadyRead( 60000 ) )
	{
		// error: timeout waiting for response
		return;
	}

	list<string> result_buf;
	while( socket->canReadLine() )
	{
		string line_received( socket->readLine().data() );
		result_buf.push_back( line_received );
	}
	socket->close();

The client connects and writes some data. After that, it is waiting for response but runs into a time out. The same code worked with an earlier version of Qt (5.0 or 5.2) running under Windows 7 32-bit, compiled with VS2010. Now it is compiled with VS2013 Community Edition for 64-bit. Firewall is switched off. I started the server in debug mode but nothing happens, incommingConnection() is not called.
What am I doing wrong?

regards, Karl

[SGaist]

Hi,

Might be a silly question but, did you check what QTcpSocket::error() returns ?

[karl_qt]

Yes, I checked the error message. It says "Network connection timed out". If I don't start the server, QTcpSocket returns the error string "Connection refused". So I guess, there is some kind of connection, but something is missing.

[mcosta]

Hi,

QTcpServer::incomingConnection() accepts a qintptr as parameter and it is defined as qint64 in a 64 bits platform.
You're using intthat is 32 bit; this also explain why your code works when compiler in 32bit.

If you're using C++11 I suggest to use the override keyword to get informed when you're doing similar mistakes; Qt also offers Q_DECL_OVERRIDE to make your code compatible also for C++99

[karl_qt]

Thank you very much!
That solved my problem.

[sarielv]

I just wanted to tack a me-too on here. I've been converting a QTcpServer app over to 64-bit and it immediately stopped receiving signal. Connecting a 64-bit client to a 32-bit server still worked, so the problem had to be in the 64-bit server or one of the dependencies. As it turned out, the incomingConnection() had an int argument instead of a qintptr, a change we missed when upgrading to Qt5.