Question

我知道可能已经提出了一些类似的问题，但我发现的问题的答案涵盖了非常具体的问题，我仍然没有想出来。

在我的程序中，我正在创建一个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有一个插槽，接受带有数据（sendData(QByteArray)）的QByteArray。该数组的全部内容被视为一个“消息”，并将它们写入套接字。我想要执行以下操作：每次写入消息时，我希望接收QPeer仅发出一次信号dataReceived(QByteArray)，即包含整个消息的QByteArray。（注意：所有信号/插槽，包括连接QPeer及其套接字的私有信号/插槽以及sendData(QByteArray)等公共信号/插槽，都会在必要时使用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sendData中调用QTcpSocket::write()一次，然后假设对于我做的每次写操作，另一端的QTcpSocket只生成一个readyRead信号。那我该怎么办？

这是我的想法，请告诉我这是否有效：

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);
}

读：

现在我希望read函数（连接到QTcpSocket::readyRead()）使用头（指定消息长度的4字节int）然后读取该字节数;接下来用恰好那些字节发出dataReceived。我在尝试这样做时遇到了严重的麻烦。 例如：如果发出readyRead怎么办，我可以读取消息的标题，但不能读取指定的字节数？或者如果仅部分收到标题会怎么样？

1。如何正确地将标头（4字节int）写入套接字？

2。如何正确实现读取功能以使其达到我想要的效果？

欢迎任何提示。谢谢！

Answer 1

我参与了一个符合您期望的项目，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：

已编辑，已添加对服务器处理多个客户端的支持。

Client.h：

#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：不要使用此方法传输大文件，因为使用此方法，邮件的全部内容在发送之前都会放入内存中，这会导致内存使用率过高。并且因为32位有符号INT的最大值为2,147,483,647，如果输入数据的值高于字节数，则无效。小心。

Answer 2

如你所说，你需要等待你的标题完全发送，然后再读取它，然后读取好的字节数并发出信号以便数据可用。

这是一个例子（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
       }
    }
}

QTcpSocket：读写

2 个答案: