我曾经使用UNIX C++ sockets建立了一个socket连接,在连接后,我使用循环逐字节读取数据,直到读取完整条消息。我知道我将要接收的消息的前两个字节以及其长度(15个字节)。因此,我的函数看起来像这样:
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;
}
现在我正在使用QTcpSockets进行相同的实现。连接已经建立,然后我调用:
if(socket->waitForReadyRead(Global::tiempoMaximoDeEsperaParaRecibirDatosMastil)){
/* Read socket to find a valid packet */
if (findPacket(socket, &messageReceived)) {
qDebug()<<"New packet found!";
//...
}
}
所以我在等待某些信息准备好后再调用findPacket,它现在几乎相同,一次读取一个字节:
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;
}
看起来很相似,但它不起作用。一旦我等待waitForReadyRead,我进入findPacket的循环,并能够读取接收到的前4个字节。之后,没有更多数据被接收。它仍然在findPacket的循环中检查,但是read函数总是返回0个字节的读取。没有接收到新信息。这是不可能的,因为服务器每隔几毫秒就发送同一个数据包,所以即使我丢失了一些数据,最终我应该读取到一些内容。
那么,我做错了什么?我应该用不同的方式等待吗?第一次read函数返回0个字节时,我应该再次等待吗?这个read函数和C++库中的函数有什么区别?