c++ - 如何在Qt中读取下一个数据包

Question

我的客户端设置如下:客户端首先发送一个数据包，其中包含要从套接字读取的实际数据的长度。然后客户端自己发送实际数据。 (我在实际发送数据之前预先设置了数据包长度)。

我想知道如何在 Qt Creator 中读取下一个数据包。我收到一条错误消息，提示未找到此类插槽:MyThread::readPacket (int)。我做错了什么？

(如果我读取的字节数错误，请忽略该部分)

我的服务器端代码如下:

#include "thread.h"
#include <QDebug>
#include "DataSetProtos.pb.h"
MyThread::MyThread(qintptr ID, QObject *parent) :
QThread(parent)
{
    this->socketDescriptor = ID;
}

void MyThread::run()
{
// thread starts here
    qDebug() << " Thread started";

    socket = new QTcpSocket();

// set the ID
  if(!socket->setSocketDescriptor(this->socketDescriptor))
{
    // something's wrong, we just emit a signal
    emit error(socket->error());
    return;
}

// connect socket and signal
// note - Qt::DirectConnection is used because it's multithreaded
//        This makes the slot to be invoked immediately, when the signal is emitted.

connect(socket, SIGNAL(readyRead()), this, SLOT(readyRead()), Qt::DirectConnection);
connect(socket, SIGNAL(disconnected()), this, SLOT(disconnected()));

// We'll have multiple clients, we want to know which is which
qDebug() << socketDescriptor << " Client connected";

// make this thread a loop,
// thread will stay alive so that signal/slot to function properly
// not dropped out in the middle when thread dies

exec();
}

void MyThread::readyRead()
{
// get the information
char* buffer = new char[SIZE];
int iResult= socket->read(buffer, SIZE);

connect(socket,SIGNAL(readyRead()), this,     SLOT(readPacket(iResult)), Qt::DirectConnection);
}

void MyThread::readPacket(int bufferLength)
{
char *buffer = new char[bufferLength];
int iResult = socket->read(buffer, bufferLength);
printf("\n Read 2 : %d", iResult);

}

void MyThread::Print(Visualization::PacketData packet)
{
    printf("\n\nPacket Name : %s", packet.name());
    printf("\n Packet length : %d ", packet.length());
}

void MyThread::disconnected()
{
qDebug() << socketDescriptor << " Disconnected";


    socket->deleteLater();
exit(0);
}

我的thread.h文件如下:

#ifndef THREAD_H
#define THREAD_H

#include <QThread>
#include <QTcpSocket>
#include <QDebug>
#include "DataSetProtos.pb.h"

#define SIZE 500
class MyThread : public QThread
{
    Q_OBJECT
public:
    explicit MyThread(qintptr ID, QObject *parent = 0);

void run();

signals:
void error(QTcpSocket::SocketError socketerror);

public slots:
void readyRead();
void readPacket( int bufferLength);
void disconnected();
void Print( Visualization::PacketData packet );

private:
QTcpSocket *socket;
qintptr socketDescriptor;
};

#endif // THREAD_H

Answer 1

正如 MrPickles 指出的那样，您让自己很难过。但是，您不需要一直更改数据格式。您只需要在不需要时停止尝试使用线程。 Qt 中几乎没有任何东西需要使用线程，除了繁重的数据处理或类似的事情。绝对不是基本的网络 I/O。

我有一个应用程序正在与消息长度前缀的 protobufs 通信。这是我的 onReadyRead 实现的要点，更改了一些细节并删除了不必要的内容:

void ProtobufMessageReceiver::onReadyRead()
{
    //Some maximum size of a message to protect from malformed
    //packets or bugs. This value should be above the size of the largest
    //protobuf message you ever expect to receive.
    static const uint32_t MAX_ALLOWED_SIZE = 1024 * 1024; //1MB

    uint32_t msg_size;
    while ( m_socket->bytesAvailable() >= sizeof(msg_size) )
    {
        m_socket->peek(reinterpret_cast<char*>(&msg_size), sizeof(msg_size));

        //OK, we have read in a 32-bit message size, now verify that
        //it is valid before we try to read that many bytes on the socket

        if ( msg_size > MAX_ALLOWED_SIZE )
        {
            //You might throw an exception here or do some other error
            //handling. Like most Qt code, though, this app doesn't
            //use exceptions, so we handle a malformed packet by just
            //closing the socket. In a real app you'd probably at least
            //want to do some logging here, as this should be a very
            //abnormal case and signifies a bug on the sending end.
            m_socket->close();
            break;
        }

        //Now check to see if we have that many bytes available to read in.
        //If we do, we have at least one full message waiting to process, if not,
        //we'll process the message on the next call to onReadyRead.
        if ( m_socket->bytesAvailable() >= sizeof(msgSize) + msgSize )
        {
            m_socket->read(reinterpret_cast<char*>(&msg_size), sizeof(msg_size));

            QScopedArrayPointer<char> buffer(new char[msgSize]);
            m_socket->read(&buffer[0], msgSize);
            processMessage(buffer, msgSize);
        }
        else
        {
            break;
        }
    }
}

processMessage 函数现在将始终处理一个单一的、完全有效的 protobuf 流，可以使用 parseFromArray 对其进行解码。 (在这个例子中，我们可能会使用一个 protobuf Union Type 在一个流中交错几种不同的类型)。请注意，因为不能保证 onReadyRead 会为每个 protobuf 消息调用一次，所以在其中设置 while 循环非常重要。无论您使用的是 Qt 还是使用套接字的其他方式，情况都是如此，因为 TCP 只是一个字节流，并不划定消息边界。毕竟，这就是我们甚至必须首先处理长度前缀的全部原因。