QTcpSocket::readyRead() lost messages, performance issue?

[Juba]

Hi all,
I have a trouble with QTcpSocket readyRead() signal.
My Qt application act as client and the server send messages in an asyncronous way.
The problem is that I notice that sometimes a message isn't signaled by the readyRead().
The message is always the same message in the sequence, but the problem don't always occours.
I'm sure that message comes because I see the network traffic with wireshark.

Here is my client code:

{
// in class ctor...
  m_socket = new QTcpSocket(this);
  connect(m_socket, SIGNAL(connected()),                           this,SLOT(connected()));
  connect(m_socket, SIGNAL(error(QAbstractSocket::SocketError)),      this,SLOT(error(QAbstractSocket::SocketError)));
  connect(m_socket, SIGNAL(disconnected()),                        this,SLOT(disconnected()));
  connect(m_socket, SIGNAL(readyRead()),                           this,SLOT(receiveMessage()));
}
 
void XmlSocket::receiveMessage()
{
    int bytesRead;
    // READ_BUF_SIZE is defined as 512 and the message I receive are 100 chars...
    char buf[READ_BUF_SIZE];
 
    // read data from socket
    // NB: loop only if we read more than 512 bytes...
    QString msgString;
    do {
        bzero(buf,READ_BUF_SIZE);
 
        bytesRead = m_socket->read(buf, READ_BUF_SIZE);
        if(bytesRead < 0)
            qCritical("Error reading data from socket %d",bytesRead);
        else if(bytesRead == 0)
            qWarning("No more data on socket...");
 
        msgString += QString(buf);
        qDebug("++ %s", qPrintable(msgString));
    } while(bytesRead == READ_BUF_SIZE);
 
    // emit signal with available data
    QDomDocument msg;
    if(!msg.setContent(msgString))
        qWarning("Error setting content for string %s", qPrintable(msgString));
 
    emit messageReceived(msg);
}

{
// in class ctor...
  m_socket = new QTcpSocket(this);
  connect(m_socket, SIGNAL(connected()),                           this,SLOT(connected()));
  connect(m_socket, SIGNAL(error(QAbstractSocket::SocketError)),      this,SLOT(error(QAbstractSocket::SocketError)));
  connect(m_socket, SIGNAL(disconnected()),                        this,SLOT(disconnected()));
  connect(m_socket, SIGNAL(readyRead()),                           this,SLOT(receiveMessage()));
}

void XmlSocket::receiveMessage()
{
    int bytesRead;
    // READ_BUF_SIZE is defined as 512 and the message I receive are 100 chars...
    char buf[READ_BUF_SIZE];

    // read data from socket
    // NB: loop only if we read more than 512 bytes...
    QString msgString;
    do {
        bzero(buf,READ_BUF_SIZE);

        bytesRead = m_socket->read(buf, READ_BUF_SIZE);
        if(bytesRead < 0)
            qCritical("Error reading data from socket %d",bytesRead);
        else if(bytesRead == 0)
            qWarning("No more data on socket...");

        msgString += QString(buf);
        qDebug("++ %s", qPrintable(msgString));
    } while(bytesRead == READ_BUF_SIZE);

    // emit signal with available data
    QDomDocument msg;
    if(!msg.setContent(msgString))
        qWarning("Error setting content for string %s", qPrintable(msgString));

    emit messageReceived(msg);
}

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I have see that the message that I don't receive is sent just 3 ms after the previous one...
Send time
[28/04 16:33:30:423] message 1, received
[28/04 16:33:30:525] message 2, received
[28/04 16:33:30:528] message 3, NOT RECEIVED
[28/04 16:33:31:290] message 4, received

This could be a performance issue???

Now I try to solve using standard socket, but I wish to use QTcpSocket because they offer a simple API and for portability reason.

I am using Qt 4.7.1 on linux platform.