QTcpSocket:读写

Question

我知道有些类似的问题可能已经问过了，但我发现的答案涵盖了非常具体的问题，但我仍然没有弄清楚。

在我的程序中，我创建了一个QObject (称为QPeer)，它使用QTcpSocket通过网络与另一个这样的对象进行通信。QPeer有一个接受带有数据的QByteArray (sendData(QByteArray))的插槽。该数组的整个内容被认为是一个“消息”，并被写入套接字。我想做以下工作:每次写入消息时，我都希望接收QPeer只发出一次信号dataReceived(QByteArray)，即包含整个消息的QByteArray。(注意:所有信号/插槽，包括连接QPeer与其套接字的私有信号/时隙和公共信号/插槽(如sendData(QByteArray) )，都在必要时使用Qt::QueuedConnection进行序列化。)

我使用信号QTcpSocket::readyRead()从套接字进行异步读取。现在我知道我不能只在QTcpSocket::write()中调用sendData一次，然后假设每写一次，另一边的QTcpSocket就会产生一个readyRead信号。那我该怎么办？

这是我的主意，请告诉我这是否可行：

写作：

void QPeer::sendData(QByteArray data)
{
    // TODO: write data.size() as raw int of exactly 4 bytes to socket
    const char *bytes = data.constData();
    int bytesWritten = 0;
    while (bytesWritten < data.size())
        bytesWritten += _socket->write(bytes + bytesWritten);
}

阅读：

现在，我希望read函数(连接到QTcpSocket::readyRead())使用标头(指定消息长度的4字节int )，然后读取该字节数；接下来，使用这些字节发出dataReceived。我很难做到这一点。例如:如果发出readyRead并且我可以读取消息的头，但不能读取指定的字节数，该怎么办？或者，如果只有部分接收到标头怎么办？

1.如何正确地将头(4字节int)写入套接字？

2.如何正确地实现read函数，以便它能实现我想要的？

任何小费都欢迎。谢谢!

Answer 1

我做了一个项目，做的和你期望的一样，在这里看到我为我们的问题开发的解决方案，简化为更容易理解：

编辑，增加了对服务器的支持，可以处理多个客户端.

客户：

#include <QtCore>
#include <QtNetwork>

class Client : public QObject
{
    Q_OBJECT
public:
    explicit Client(QObject *parent = 0);

public slots:
    bool connectToHost(QString host);
    bool writeData(QByteArray data);

private:
    QTcpSocket *socket;
};

Client.cpp：

#include "client.h"

static inline QByteArray IntToArray(qint32 source);

Client::Client(QObject *parent) : QObject(parent)
{
    socket = new QTcpSocket(this);
}

bool Client::connectToHost(QString host)
{
    socket->connectToHost(host, 1024);
    return socket->waitForConnected();
}

bool Client::writeData(QByteArray data)
{
    if(socket->state() == QAbstractSocket::ConnectedState)
    {
        socket->write(IntToArray(data.size())); //write size of data
        socket->write(data); //write the data itself
        return socket->waitForBytesWritten();
    }
    else
        return false;
}

QByteArray IntToArray(qint32 source) //Use qint32 to ensure that the number have 4 bytes
{
    //Avoid use of cast, this is the Qt way to serialize objects
    QByteArray temp;
    QDataStream data(&temp, QIODevice::ReadWrite);
    data << source;
    return temp;
}

Server.h：

#include <QtCore>
#include <QtNetwork>

class Server : public QObject
{
    Q_OBJECT
public:
    explicit Server(QObject *parent = 0);

signals:
    void dataReceived(QByteArray);

private slots:
    void newConnection();
    void disconnected();
    void readyRead();

private:
    QTcpServer *server;
    QHash<QTcpSocket*, QByteArray*> buffers; //We need a buffer to store data until block has completely received
    QHash<QTcpSocket*, qint32*> sizes; //We need to store the size to verify if a block has received completely
};

Server.cpp：

#include "server.h"

static inline qint32 ArrayToInt(QByteArray source);

Server::Server(QObject *parent) : QObject(parent)
{
    server = new QTcpServer(this);
    connect(server, SIGNAL(newConnection()), SLOT(newConnection()));
    qDebug() << "Listening:" << server->listen(QHostAddress::Any, 1024);
}

void Server::newConnection()
{
    while (server->hasPendingConnections())
    {
        QTcpSocket *socket = server->nextPendingConnection();
        connect(socket, SIGNAL(readyRead()), SLOT(readyRead()));
        connect(socket, SIGNAL(disconnected()), SLOT(disconnected()));
        QByteArray *buffer = new QByteArray();
        qint32 *s = new qint32(0);
        buffers.insert(socket, buffer);
        sizes.insert(socket, s);
    }
}

void Server::disconnected()
{
    QTcpSocket *socket = static_cast<QTcpSocket*>(sender());
    QByteArray *buffer = buffers.value(socket);
    qint32 *s = sizes.value(socket);
    socket->deleteLater();
    delete buffer;
    delete s;
}

void Server::readyRead()
{
    QTcpSocket *socket = static_cast<QTcpSocket*>(sender());
    QByteArray *buffer = buffers.value(socket);
    qint32 *s = sizes.value(socket);
    qint32 size = *s;
    while (socket->bytesAvailable() > 0)
    {
        buffer->append(socket->readAll());
        while ((size == 0 && buffer->size() >= 4) || (size > 0 && buffer->size() >= size)) //While can process data, process it
        {
            if (size == 0 && buffer->size() >= 4) //if size of data has received completely, then store it on our global variable
            {
                size = ArrayToInt(buffer->mid(0, 4));
                *s = size;
                buffer->remove(0, 4);
            }
            if (size > 0 && buffer->size() >= size) // If data has received completely, then emit our SIGNAL with the data
            {
                QByteArray data = buffer->mid(0, size);
                buffer->remove(0, size);
                size = 0;
                *s = size;
                emit dataReceived(data);
            }
        }
    }
}

qint32 ArrayToInt(QByteArray source)
{
    qint32 temp;
    QDataStream data(&source, QIODevice::ReadWrite);
    data >> temp;
    return temp;
}

注意：不使用此方法来传输大文件，因为使用此方法，消息的全部内容在发送之前都放在内存中，这会导致内存的高使用率。因为32位有符号的INT有最大值给2,147,483,647，如果输入数据的值大于字节，它就不能工作。保重。

Answer 2

如前所述，在读取头之前，需要等待头完全发送，然后读取大量字节，并发出数据可用性信号。

这里有一个例子(未经测试)：

//header file

class Peer {
//[...]
protected:
   bool m_headerRead; //initialize to false
   unsigned int m_size_of_data_to_read;
//[...]
};

//source file
void QPeer::sendData(QByteArray data)
{
  int size = data.size();
  _socket->write((const char*) &size, sizeof(int);
  //use directly QIODevice::write(QByteArray)
  _socket->write(data);
}

void QPeer::readData()
{
    int bytes = _socket->bytesAvailable();
    bool contains_enough_data = true;

    while (contains_enough_data) {
       if (! m_headerRead && _socket->bytesAvailable() >= sizeof(int)) {
         //read header only and update m_size_of_data_to_read
         m_headerRead = true;
        } else if (m_headerRead && _socket->bytesAvailable >= m_size_of_data_to_read) {
          //read data here
          m_headerRead = false;
          emit dataAvailable();
       } else {
           contains_enough_data = false; //wait that further data arrived
       }
    }
}