QTCP and packet parsing

Taz742

@Jonnybravo
not need array.
QDataStream are best way, for my point of view.
Here you can see how to use QDataStream
https://forum.qt.io/topic/84222/qdatastream-serialze-deserialize-myclass-pointer/2
It would be nice if you read everything in the end.

VRonin

Let's imagine your ce06000038000000010000000000000068656c6c6f616c6c00 is one 32bit signed integer and a QString.

QTcpSocket *socket = qobject_cast<QTcpSocket *>(socketObject);
if(!socket) return;
QDataStream streamer(socket);
streamer.startTransaction();
qint32 val1;
QString val2;
streamer >> val1 >> val2;
if(streamer.commitTransaction()){
qDebug() << "Read successful: " << val1 << val2;
}

Jonnybravo

The only issue with datastreams is that the data is always changing very rarely do you see the same data twice. So i understand that hes breaking up the data into variables.

qint32 val1;
QString val2;
streamer >> val1 >> val2;

Before in my C++ app i would create a unsigned char vector resize the vector to the recvd size of the socket create a template that would loop thru the position base on the value i sent to it.

its mostly about being able to recv the data verity it on my end and send back what i need.

VRonin

@Jonnybravo I don't think I understand what you mean

SGaist

Isn't the information structure what you are sending around ?

Jonnybravo

The information is not known i am just recving traffic from a tcp connection and trying to parse the data so that i can read it and check its validations on my end before replying back.

//Something like this i can do
//ce06000038000000010000000000000068656c6c6f616c6c00
qint8 header = recvdbuffer[0];
qint8 opcode = recvdbuffer[1];
qint8 size = recvdbuffer[4];
for(unsigned i = 0; i < recvdbuffer.length(); i++ )
{
// grab the string from the array
}

SGaist

How do you know when you received a full frame of data ?

Jonnybravo

The client builds the packet into one big buffer and sends it. On the server side i know the size and most data in the frame.

Qt just has a crap way of being able to have a dynamic way of extracting data from a socket.

The only methods i can think of off the top of my head is use qdatastream that is built on top of the data structure of what you are reading then pass the infomation into arguments later on to be used for whatever you need it for.

example:

QTcpSocket *socket = qobject_cast<QTcpSocket *>(socketObject);
if(!socket) return;
QDataStream streamer(socket);
streamer.startTransaction();

streamer >> val1 >> val2 >> val3 >> val4;

switch (val2)
case: // do what you need with val2 with a function that takes arguments val4 and val5
break;

SGaist

If your client is sending the information structure, why not implement the stream operators for that structure directly ? That way you'll have directly an information object to handle on the receiving end.

VRonin

You can always use startTransaction on the socket without using QDataStream

Jonnybravo

Could you tell me what im doing wrong here.. (qbyte array to qvector)

So ive created a class that gets data from a struct vector buffer

struct Packet
{
    public:
        QVector<quint8>Buffer;
        quint8 Header;
        quint8 OpCode;

public:
    Packet( ) {}
    Packet( int size ) : Buffer(size){ }

	/* Read values from packet */
    template <typename T> T Get( quint32 pos )
	{
		if( Buffer.size() < pos+sizeof(T) ) 
                      return 0;
		return *((T*)&Buffer[pos]);
	}
    quint8 GetByte( quint32 pos )
	{
        return Get<quint8>( pos );
	}
    quint16 GetWord( quint32 pos )
	{
        return Get<quint16>( pos );
	}
    unsigned GetDWord( quint32 pos )
	{
		return Get<unsigned>( pos );
	}
    quint64 GetQWord( quint32 pos )
	{
        return Get<quint64>( pos );
	}
    float GetFloat( quint32 pos )
	{
		return Get<float>( pos );
	}
    void GetString( quint32 pos, char* buffer )
	{	  
		unsigned strLen = GetDWord( pos );
		for(unsigned i = 0; i < strLen; i++ )
		{
            buffer[i] = Get<quint8>(pos+4+i);
		}
		buffer[strLen] = 0;
	}
};

So i am now trying to convert the data from qbyte to vector.

// Recv the entire buffer from bytesAvailable()
recvbuffer = socket->readAll();
Packet m_pak(recvbuffer.size());

QDataStream out(&recvbuffer ,QIODevice::WriteOnly);
out << m_pak.Buffer;

//doesnt fill the buffer with the qbytearray..

Now should i just instead of using datastream just resize it and insert the qbytearray into the vector.

recvbuffer = socket->readAll();
Packet m_pak(MAX_BUFFER);
m_pak.Buffer.resize(m_pak.Buffer.size() + recvbuffer.size());
memcpy(&m_pak.Buffer[m_pak.Buffer.size() - recvbuffer.size()], &recvbuffer[0], recvbuffer.size() * sizeof(int));

doesnt work..

recvbuffer = socket->readAll();
Packet m_pak(MAX_BUFFER);
m_pak.Buffer.reserve(m_pak.Buffer.size() + recvbuffer.size());
qCopy(&recvbuffer[0], &recvbuffer[recvbuffer.size()], std::back_inserter(m_pak.Buffer));
//crashes due to the inserter copy.

Any ideas in how to fix this or what i should do...

SGaist

How do you know you received the full data ?

Jonnybravo

i do a checksum on the packet size and of that of the header. if the data matches to what it should be i parse it..

any sugguestions how to fix my issue?

jsulm

@Jonnybravo Why do you want to use QVector for your buffer instead of QByteArray?

J.Hilk

@Jonnybravo

I don't quite get why you're doing this, but this, should work:

m_pak.Buffer.clear();
for(int i(0); i < recvbuffer .size(); i++)
    m_pak.Buffer.append(static_cast<int>(recvbuffer.at(i));)

I'm not sure if you'll need the cast, but I added it, just to be sure ;-)