Issue using QTcpSocket - works for QString but not for QImage

[jamo_]

Hi,

I have written a server/client, initially using the Fortune examples. The data received is a QVariant - so the QVariant type can be used to determine what to do with the data.

Apologies if my explanations are not great - I am not great with describing what I want to do/have done in programming-speak.

For e.g. a QString it works fine (I guess as it comes in one block?). however attempting with a QImage -> the version/description/data type are sent OK --> If I output the emit_message in read_client then it outputs these OK. I assume this is because the images are larger and need to be sent in multiple blocks. Hence I believe the readClient() would be called multiple times for the same serialized data item. I can't work out how to deal with this gracefully - should I create some function to deal with whether this is a fresh readClient() or one to deal with data that is mid-transmission?
Either that, or I need some sort of loop based on data/the size sent in the header, to build up "data" from the blocks/packets received but am unsure of how to go about doing this. I also send an end of data flag - could this also be used? I have looked through the forums - there are multiple issues on this topic, but I could not find a specific answer (well not with the search terms I have been using)...

Any help would be much appreciated (as well as any pointers if my code is poor -> I am a bit of a QT noob)..

Here is a stripped down version of the codes.

Server:

void Server::incomingConnection(int socketId) {
	   	ServerSocket *socket = new ServerSocket(this);
	    socket->setSocketDescriptor(socketId);
}
 
 
ServerSocket::ServerSocket(QObject *parent) : QTcpSocket(parent)
{
	connect(this, SIGNAL(readyRead()), this, SLOT(readClient()));
	connect(this, SIGNAL(disconnected()), this, SLOT(deleteLater()));
	blockSize = 0;
}
 
void ServerSocket::readClient()
{
    QDataStream in(this);
    in.setVersion(QDataStream::Qt_4_5);
    if (blockSize == 0) {
        if (bytesAvailable() < (sizeof(quint16)))
            return;
        in >> blockSize;
    }
    if (bytesAvailable() < (quint16)(blockSize + sizeof(quint16) + sizeof(quint8)))
        return;
    quint8 version;
    QString description;
    QVariant data;
    quint16 endFlag;
    in >> version;
    in >> description;
	in >> data;
	in >> endFlag;
 
	QString emit_message  = "\n\tVersion: " + QString::number(version) +
							"\n\tType(" + QString(data.typeName()) + "): " + QString::number(data.type()) +
							"\n\tSize: " + QString::number(blockSize) +
							"\n\tMessage: " + description +
							"\n\tData: " + data.toString() +
							"\n\tEndFlag: " + QString::number(endFlag);
 
}

void Server::incomingConnection(int socketId) {
	   	ServerSocket *socket = new ServerSocket(this);
	    socket->setSocketDescriptor(socketId);
}


ServerSocket::ServerSocket(QObject *parent) : QTcpSocket(parent)
{
	connect(this, SIGNAL(readyRead()), this, SLOT(readClient()));
	connect(this, SIGNAL(disconnected()), this, SLOT(deleteLater()));
	blockSize = 0;
}

void ServerSocket::readClient()
{
    QDataStream in(this);
    in.setVersion(QDataStream::Qt_4_5);
    if (blockSize == 0) {
        if (bytesAvailable() < (sizeof(quint16)))
            return;
        in >> blockSize;
    }
    if (bytesAvailable() < (quint16)(blockSize + sizeof(quint16) + sizeof(quint8)))
        return;
    quint8 version;
    QString description;
    QVariant data;
    quint16 endFlag;
    in >> version;
    in >> description;
	in >> data;
	in >> endFlag;

	QString emit_message  = "\n\tVersion: " + QString::number(version) +
							"\n\tType(" + QString(data.typeName()) + "): " + QString::number(data.type()) +
							"\n\tSize: " + QString::number(blockSize) +
							"\n\tMessage: " + description +
							"\n\tData: " + data.toString() +
							"\n\tEndFlag: " + QString::number(endFlag);

}

To copy to clipboard, switch view to plain text mode 

client:

//this is fired on the click of a QPushButton
void Client::sendRequest()
{
        QTcpSocket socket;
        socket.connectToHost(serverName, serverPort);
 
        if (!socket.waitForConnected(TIMEOUT)) {
            emit error(socket.error(), socket.errorString());
            return;
        }
 
        QVariant data;
QString description;
//text is set in a QLineEdit
        if (text == "image") {
        	data = QImage("someimage.jpg");
        	description = "This is an image";
        }
        else {
        	data = text;
        	description = "This is some text";
        }
 
        QByteArray block;
        QDataStream out(&block, QIODevice::WriteOnly);
		out.setVersion(QDataStream::Qt_4_5);
        out << quint16(0) << quint8(1) << description << data << quint16(0xFFFF);
		out.device()->seek(0);
		out << (quint16)(block.size() - sizeof(quint16) - sizeof(quint8) - sizeof(quint16));
		socket.write(block);
		socket.flush();
		qDebug() << "Sending: [" + description + data.toString()
								+ "] to server(" + serverName + ":" + QString::number(serverPort) + ")";
}

//this is fired on the click of a QPushButton
void Client::sendRequest()
{
        QTcpSocket socket;
        socket.connectToHost(serverName, serverPort);

        if (!socket.waitForConnected(TIMEOUT)) {
            emit error(socket.error(), socket.errorString());
            return;
        }

        QVariant data;
QString description;
//text is set in a QLineEdit
        if (text == "image") {
        	data = QImage("someimage.jpg");
        	description = "This is an image";
        }
        else {
        	data = text;
        	description = "This is some text";
        }

        QByteArray block;
        QDataStream out(&block, QIODevice::WriteOnly);
		out.setVersion(QDataStream::Qt_4_5);
        out << quint16(0) << quint8(1) << description << data << quint16(0xFFFF);
		out.device()->seek(0);
		out << (quint16)(block.size() - sizeof(quint16) - sizeof(quint8) - sizeof(quint16));
		socket.write(block);
		socket.flush();
		qDebug() << "Sending: [" + description + data.toString()
								+ "] to server(" + serverName + ":" + QString::number(serverPort) + ")";
}

To copy to clipboard, switch view to plain text mode 

Thanks,

James

[wysota]

What do you send as the block size?

[jamo_]

Hi Wysota,

Is it not (line 27 of the client code):

out << (quint16)(block.size() - sizeof(quint16) - sizeof(quint8) - sizeof(quint16));

out << (quint16)(block.size() - sizeof(quint16) - sizeof(quint8) - sizeof(quint16));

To copy to clipboard, switch view to plain text mode 

?

Which is the size of everything minus itself(quint16), the version(quint8) and the endFlag(quint16). I have tried casting it to a quint64 and 32 instead but this makes no difference. Although that was a few days ago so i will try this again now.

Thanks,

James

[wysota]

What is "everything"? blocksize determines how much data needs to be available before the reading function tries to read the next request from the stream. Furthermore you are doing some complicated operations regarding filling the data stream with proper information, writing some 0, then some 1 and then trying to overwrite them with something else (the block size, I guess).