I had a socket connection with UNIX C++ sockets where, after connecting, I had a loop for reading byte by byte until I had the full msg. I know the first two bytes of the message I'm going to receive, and its length (15 bytes). So the function looked like:
bool mastControl::findPacket(int sockfd, st_messageMastToPc * messageReceived, bool * connected) {
int n = 0;
bool messageFound = false;
char * buffer = (char *) messageReceived;
unsigned int pos = 0;
while ( ((n = read(sockfd, &(buffer[pos]), 1)) > 0) and not messageFound) {
if (n == 1) {
pos++;
if ( (pos == 1) && (buffer[0] == 0x02)) { // First byte to receive
std::cout << "INFO - Rcv1" << std::endl;
} else if ( (pos == 2) && (buffer[1] == 0x33) ) { // Second byte
std::cout << "INFO - Rcv2" << std::endl;
} else if (pos >= uiMessageMastToPcSize) { // Full msg received
messageFound = true;
std::cout << "INFO - Complete message received" << std::endl;
} else if (pos <= 2) { // Wrong values for the first 2 bytes
std::cout << "WARN - Reseting (byte " << pos << " -> " << int(pos) << ")" << std::endl;
pos = 0;
}
}
}
if (n < 0){
//EROR
*connected = false;
}
return messageFound;
}
Now I'm implementing the same with QTcpSockets. Connection is established, and then I call:
if(socket->waitForReadyRead(Global::tiempoMaximoDeEsperaParaRecibirDatosMastil)){
/* Read socket to find a valid packet */
if (findPacket(socket, &messageReceived)) {
qDebug()<<"New packet found!";
//...
}
}
So I'm waiting until there is some info ready yo be read, and then call findPacket, which is now almost the same, reading byte by byte:
bool mastControl::findPacket(QTcpSocket *socket, st_messageMastToPc * messageReceived) {
int n = 0;
bool messageFound = false;
char * buffer = (char *) messageReceived;
unsigned int pos = 0;
while ( ((n = socket->read(&(buffer[pos]), 1)) >= 0) and not messageFound) {
if (n == 1) {
qDebug()<<"Recibido: "<<buffer[pos]<<", en pos: "<<pos;
pos++;
if ( (pos == 1) && (buffer[0] == 0x022)) {
qDebug()<<"0x02 in first position";
// std::cout << "INFO - Rcv1" << std::endl;
} else if ( (pos == 2) && (buffer[1] == 0x33) ) {
qDebug()<<"0x33 in second";
std::cout << "INFO - Rcv2" << std::endl;
} else if (pos >= uiMessageMastToPcSize) {
messageFound = true;
std::cout << "INFO - Complete message received" << std::endl;
} else if (pos <= 2) {
std::cout << "WARN - Reseting (byte " << pos << " -> " << int(pos) << ")" << std::endl;
pos = 0;
}
}
}
if (n < 0){
qDebug()<< "Disconnected. Reason: " << socket->errorString();
}
return messageFound;
}
Looks pretty the same, but it doesn't work. Once I have waited on waitForReadyRead, I enter findPacket's loop and I am able to read the first 4 bytes received. After that, no more data is received. It remains inside findPacket's loop checking again, and again, and again, but read function always return 0 bytes read. No new info is received. Which is impossible, because server is sending the same packet once every few ms, so even if I loss some data, eventually I should be reading something.
So, what I am doing wrong? Should I wait in a different way? Should I wait again the first time read function returns 0 bytes read? What's the difference between this read function and the C++ libraries one?