cannot read correct len from socket

[saman_artorious]

it doesn't help. it gives terrible large numbers.

is the byte array is "47dannie", reading 4 bytes would I think, read 47da, next time it would read nnie, converting them into integers.

int len;
char *data;
client.read((char*)&len, 4); 
client.read(&data[0], len);

int len;
char *data;
client.read((char*)&len, 4); 
client.read(&data[0], len);

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this is not correct.

[Jonny174]

void MyServer::slotReadClient()
{
  QTcpSocket* pClientSocket = (QTcpSocket *)sender();
  QDataStream in( pClientSocket );
 
  in.setVersion( QDataStream::Qt_4_7 );
 
  for (;;)
  {
    if (!m_nNextBlockSize)
    {
      if (pClientSocket->bytesAvailable() < sizeof( quint16 ))
        break;
 
      in >> m_nNextBlockSize;
    }
 
    if (pClientSocket->bytesAvailable() < m_nNextBlockSize)
      break;
 
    QTime time;
    QString str;
 
    in >> time >> str;
 
    QString strMessage = time.toString() + " " + "Client has sended - " + str;
    m_ptxt->append( strMessage );
 
    m_nNextBlockSize = 0;
 
    sendToClient( pClientSocket, "Server Response: Received \"" + str + "\"" );
  }
}
 
// ----------------------------------------------------------------------
void MyServer::sendToClient( QTcpSocket *pSocket, const QString &str )
{
  QByteArray arrBlock;
  QDataStream out( &arrBlock, QIODevice::WriteOnly );
 
  out.setVersion( QDataStream::Qt_4_7 );
  out << quint16(0) << QTime::currentTime() << str;
 
  out.device()->seek(0);
  out << quint16( arrBlock.size() - sizeof( quint16 ) );
 
  pSocket->write( arrBlock );
}

void MyServer::slotReadClient()
{
  QTcpSocket* pClientSocket = (QTcpSocket *)sender();
  QDataStream in( pClientSocket );

  in.setVersion( QDataStream::Qt_4_7 );

  for (;;)
  {
    if (!m_nNextBlockSize)
    {
      if (pClientSocket->bytesAvailable() < sizeof( quint16 ))
        break;

      in >> m_nNextBlockSize;
    }

    if (pClientSocket->bytesAvailable() < m_nNextBlockSize)
      break;

    QTime time;
    QString str;

    in >> time >> str;

    QString strMessage = time.toString() + " " + "Client has sended - " + str;
    m_ptxt->append( strMessage );

    m_nNextBlockSize = 0;

    sendToClient( pClientSocket, "Server Response: Received \"" + str + "\"" );
  }
}

// ----------------------------------------------------------------------
void MyServer::sendToClient( QTcpSocket *pSocket, const QString &str )
{
  QByteArray arrBlock;
  QDataStream out( &arrBlock, QIODevice::WriteOnly );

  out.setVersion( QDataStream::Qt_4_7 );
  out << quint16(0) << QTime::currentTime() << str;

  out.device()->seek(0);
  out << quint16( arrBlock.size() - sizeof( quint16 ) );

  pSocket->write( arrBlock );
}

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[saman_artorious]

I am not asking for the way we deal with code in qtcpsocket.
i am asking why the above code which is quite logical in C, does not work out! and how to correct it.

[nix]

What is the value of the big value you get?

[saman_artorious]

What is the value of the big value you get?

output:
newConnection
1632843572
879649133
1835094839
926183009
1634558291
1396126830
1851878753
1632843572
879649133
1835094839
926183009

the strange part is when you readLine() and use qbytearray, it contains both the digit and the string "47Saman". Though, in this case, nope

[nix]

Ok, according to the example you gave, your length seems to have a 2 octet size, if the size is fixed try this

QByteArray lenBA(2,'0');
QByteArray data;
 
client.read(lenBA.data(), 2); // read the first integer for the length
short int length  = lenBA.toShort(); // check the conversion is ok here
data.reserve(length);
 
client.read(data.data(), length  );

QByteArray lenBA(2,'0');
QByteArray data;

client.read(lenBA.data(), 2); // read the first integer for the length
short int length  = lenBA.toShort(); // check the conversion is ok here
data.reserve(length);

client.read(data.data(), length  );

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1632843572 = 0x61533734 and give in ascii : "aS74" look realy close to "47Sa" if you considering byte order issue from brutal conversion from char * to int.

[Lesiok]

the strange part is when you readLine() and use qbytearray, it contains both the digit and the string "47Saman". Though, in this case, nope

As You see the length of data is transported as characters not as binary int. So You can't read read it as binary data. You must read it as string and convert to int. Another problem : what if data length is bigger then 99 - it is 3 digits.

[saman_artorious]

what if data length is bigger then 99 - it is 3 digits.

Yes, the length of data is random and may vary. I cannot find a way to deal with this.

[Lesiok]

Yes, the length of data is random and may vary. I cannot find a way to deal with this.

This is very simple. Always send fixed number of digits with leading zeros. In example if You want to send 4 digits You should send "0047Saman".
In fact, the problem is the definition of the protocol.

[Jonny174]

X3. Maybe not all the data had to come. Shaw all read code.