[Qt-interest] large xml over the network - problem

[franki]

Wednesday 27 of April 2011 16:23:22 Jeroen.DeWachter at elis.ugent.be napisał(a):
> Hi,
>
> You do know quint16 is limited to 65536, right?
> So if you're using strings that are longer than that (and you seem to do
> just that, judging from your example), the length can't be specified
> correctly in the two bytes you are trying to use for it...

Yes... in my example block.size() on server side is 69496 and quint16 is 
limited to 65536 so... 65536 - 69496 =- 3960 and in my example quint size was 
3958 (very close), so If I change from quint16 to int (which is four bytes, 
or at least I think so?) should it be OK ?

And answering to Jason, I putted the size of packet at the beginning because 
sometimes there are lots of packets emitted from server to client, each with 
some unique data, how do I know if last message xml has ended before I start 
parsing it? I'm only beginner but wouldn't be a problem when a few xml's are 
sended one after another and client hasn't finished processing of first xml 
command when two or more has arrived. You know, what can separate xml's on 
client side? to process then one by one? I thought that I can ensure myself 
that I'm reading these xml's one by one by putting size at the beginning? 
(besides it was in fortune client example)

best regards
Marek

>
> That would certainly be an explanation for the huge discrepancy in your
> block size and the quint size...
>
> Kind regards,
>
> Jeroen
>
> Quoting franki <franki at franki.eu.org>:
> > Hi all,
> >
> > I have client-server application which exchange data using xml's
> > over the net.
> > With relatively small xml's everything goes fine, but when I try to send
> > big ones there is problem with receiving it (not always just from time to
> > time), and if I double the size of xml, they are always lost.
> > Snippet of code on server side:
> >
> > void NetThread::sendToClient(QDomDocument xml) {
> >     QByteArray block;
> >     QDataStream out(&block, QIODevice::ReadWrite);
> >     out.setVersion(QDataStream::Qt_4_0);
> >     out << (quint16)0;
> >     out << xml.toString();
> >     out.device()->seek(0);
> >     out << (quint16)(block.size() - sizeof(quint16));
> >     qDebug() <<" quint size:"<<(quint16)(block.size() - sizeof(quint16))
> >     qDebug() <<" block size:"<<block.size();
> >     qDebug() <<" string size:"<<xml.toString().size();
> >     tcpSocket->write(block);
> > }
> >
> > code on client side look's like this (dataSize is quint16):
> > void NetManager::readData() {
> >     QDataStream in(socket);
> >     in.setVersion(QDataStream::Qt_4_0);
> >     if (dataSize == 0) {
> >         if (socket->bytesAvailable() < (int)sizeof(quint16))
> >             return;
> >         in >> dataSize;
> >     }
> >     if(socket->bytesAvailable() < dataSize)
> >              return;
> >
> >     QString text;
> >     in >> text;
> >     qDebug() << " dataSize:"<<dataSize<<" received:"<<text;
> >     dataSize=0;
> >     this->parseData(text);
> >     if(socket->bytesAvailable())
> >         this->readData();
> > }
> >
> > On the server side, during transmission debug says:
> > quint size: 3958
> > block size: 69496
> > string size: 34745
> >
> > On client side when there is successful transmision I got:
> > NetManager::readData dataSize: 3958  received: "very long_xml_string"
> >
> > When there is problem with transmission I got:
> > Debug: NetManager::readData bytes: 3958  received: ""
> > Debug: NetManager::parseData parse error
> > Debug: NetManager::readData bytes: 61  received: ""
> > Debug: NetManager::parseData parse error
> > Debug: NetManager::readData bytes: 51  received: ""
> > Debug: NetManager::parseData parse error
> > Debug: NetManager::readData bytes: 56  received: ""
> > Debug: NetManager::parseData parse error
> >
> > So in second example the packet length is the same 3958 but the function
> > is called 4 times and I'm quite sure that application on server side
> > doesn't send anything except for this xml.
> > So please can someone point me on my errors?
> >
> > best regards
> > Marek
> > _______________________________________________
> > Qt-interest mailing list
> > Qt-interest at qt.nokia.com
> > http://lists.qt.nokia.com/mailman/listinfo/qt-interest
>
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