Qt客户端-服务器应用程序，“发送图像”有问题

Question

我试图通过QDataStream从客户端发送图像(OpenCV Mat)到服务器。第一项是int类型，表示缓冲区的大小。它适用于10到15张图像，然后服务器将第一张图像读取为随机数(通常为2^30)，这会导致应用程序崩溃。这是客户端，在一个循环中(图像来自周期为500ms的网络摄像头):

//1) encode to jpg
 cv::vector<uchar> buf;
 cv::imencode(".jpg", *mat, buf);
 //2) write to buffer
 QByteArray buffer;
 QDataStream out(&buffer, QIODevice::WriteOnly);
 out << int(0); // save place for an int which represents the buffer size
 for(cv::vector<uchar>::iterator it = buf.begin(); it != buf.end(); ++it)
 {
  out << *it; //write each byte
 }
 out.device()->seek(0); //write the buffer size
 out << buffer.size();
 qDebug() << "Sent " << buffer.size() << "bytes";
 qint64 bytesSent = socket->write(buffer);
 if(bytesSent < buffer.size())
 {
  if(bytesSent != -1)
  {
   qDebug() << "Transmit Error! Sent " << bytesSent << " out of " << buffer.size();
  }
  else
  {
   qDebug() << socket->errorString();
  }
 }

服务器端:

QDataStream in(socket);
 int msgSize = -1;
 //first read the size as an int
 if(socket->bytesAvailable())
 {
  in >> msgSize;
 }
 qDebug() << "Read image size: " << msgSize << "bytes";
 //wait until all bytes all available
 while(socket->bytesAvailable() < ( qint64 ) ( ( qint64 )msgSize - sizeof(int) ) )
 {
  if(!socket->waitForReadyRead())
  {
   qDebug() << "Disconnected: " << socket->errorString();
   socket->disconnectFromHost();
   break;
  }
 }
 qDebug() << "Bytes recieved: " << msgSize;

 QByteArray ba;
 quint8 byte;
 for(int i = 0; i < msgSize - 1; ++i)
 {
  in >> byte;
  ba.append(byte);
 }
        cv::Mat imgbuf = cv::Mat(FRAME_WIDTH, FRAME_HEIGHT, CV_8UC3, ba.data());
 cv::Mat matImg = cv::imdecode(imgbuf, CV_LOAD_IMAGE_COLOR);

两个插座都是QTcpSocket

输出示例:

The server side: 
Read image size: 67551 bytes 
Bytes recieved: 67551 
Read image size: 56924 bytes 
Bytes recieved: 56924 
Read image size: 70027 bytes 
Bytes recieved: 70027 
Read image size: -2046830337 bytes 
Bytes recieved: -2046830337 
Read image size: -536866742 bytes 
Bytes recieved: -536866742 
Read image size: 1179207168 bytes 
At this point it tries to read 1179207168 bytes. 
The client side: 
Sent 67551 bytes 
Sent 56924 bytes 
Sent 70027 bytes 
Sent 70277 bytes 
Sent 85633 bytes 
Sent 65155 bytes 
etc ... 

只有前三个成功。

Answer 1

首先，我认为您不需要QDataStream来完成此任务。QDataStream用于序列化/反序列化Qt类型，并且特定于您正在使用的Qt版本。由于您只是想通过网络写入uchar，因此您可以直接遍历cv::vector，并直接通过网络写入这些字节(实际上，您也不需要中间的QByteArray，因为您已经拥有原始向量的byteLength)。

然而，您可以使用QDataStream(因为您正在使用非常基本的类型，这些类型在QDataStream版本之间不太可能发生变化)，并且由于您是以这种方式开始的，因此我将相应地提供一个答案

这看起来更像(客户端):

// 1) encode to jpg
cv::vector<uchar> buf;
cv::imencode(".jpg", *mat, buf);
// 2) write to buffer, your 'protocol' assumes buffer length first, then the data.
// REMEMBER: QDataStream operates on -any- QIODevice, so no need for the extra buffer here
QDataStream out(socket, QIODevice::WriteOnly);
out << buf.size();
cv::vector<uchar>::const_iterator it;
cv::vector<uchar>::const_iterator itEnd = buf.end();
for (it = buf.begin(); it != itEnd; ++it)
    out << *it;

服务器端:

QDataStream in(socket, QIODevice::ReadOnly);
cv::vector<uchar> buf;
socket->waitForReadyRead();
qint64 bytesRead = 0;
qint64 size;
in >> size;
buf.reserve(size);
while (buf.size() < size) {
    if (!socket->bytesAvailable())
        socket->waitForReadyRead();
    qint8 byte;
    in >> byte;
    buf.push_back(byte);
}
cv::Mat imgbuf = cv::Mat(FRAME_WIDTH, FRAME_HEIGHT, CV_8UC3, buf);
cv::Mat matImg = cv::imdecode(imgbuf, CV_LOAD_IMAGE_COLOR);

注意:这些都是即兴的，它很可能无法编译，当然有更有效的方法来做这件事，但我认为它给了你一个基本的想法，你可以如何去修复你现有的代码