Fortune 服务器范例 ¶

演示如何为网络服务创建服务器。

This example is intended to be run alongside the Fortune 客户端 example or the 阻塞 Fortune 客户端范例 .

它使用 QTcpServer to accept incoming TCP connections, and a simple QDataStream based data transfer protocol to write a fortune to the connecting client (from the Fortune 客户端 example), before closing the connection.

class Server : public QDialog
{
    Q_OBJECT
public:
    explicit Server(QWidget *parent = nullptr);
private slots:
    void sendFortune();
private:
    void initServer();
    QLabel *statusLabel = nullptr;
    QTcpServer *tcpServer = nullptr;
    QVector<QString> fortunes;
};
										

The server is implemented using a simple class with only one slot, for handling incoming connections.

tcpServer = new QTcpServer(this);
if (!tcpServer->listen()) {
    QMessageBox::critical(this, tr("Fortune Server"),
                          tr("Unable to start the server: %1.")
                          .arg(tcpServer->errorString()));
    close();
    return;
}
QString ipAddress;
QList<QHostAddress> ipAddressesList = QNetworkInterface::allAddresses();
// use the first non-localhost IPv4 address
for (int i = 0; i < ipAddressesList.size(); ++i) {
    if (ipAddressesList.at(i) != QHostAddress::LocalHost &&
        ipAddressesList.at(i).toIPv4Address()) {
        ipAddress = ipAddressesList.at(i).toString();
        break;
    }
}
// if we did not find one, use IPv4 localhost
if (ipAddress.isEmpty())
    ipAddress = QHostAddress(QHostAddress::LocalHost).toString();
statusLabel->setText(tr("The server is running on\n\nIP: %1\nport: %2\n\n"
                        "Run the Fortune Client example now.")
                     .arg(ipAddress).arg(tcpServer->serverPort()));
										

In its constructor, our Server object calls listen() to set up a QTcpServer to listen on all addresses, on an arbitrary port. In then displays the port QTcpServer picked in a label, so that user knows which port the fortune client should connect to.

fortunes << tr("You've been leading a dog's life. Stay off the furniture.")
         << tr("You've got to think about tomorrow.")
         << tr("You will be surprised by a loud noise.")
         << tr("You will feel hungry again in another hour.")
         << tr("You might have mail.")
         << tr("You cannot kill time without injuring eternity.")
         << tr("Computers are not intelligent. They only think they are.");
										

Our server generates a list of random fortunes that it can send to connecting clients.

connect(tcpServer, &QTcpServer::newConnection, this, &Server::sendFortune);
										

When a client connects to our server, QTcpServer 将发射 newConnection() . In turn, this will invoke our sendFortune() slot:

void Server::sendFortune()
{
    QByteArray block;
    QDataStream out(&block, QIODevice::WriteOnly);
    out.setVersion(QDataStream::Qt_5_10);
    out << fortunes[QRandomGenerator::global()->bounded(fortunes.size())];
										

The purpose of this slot is to select a random line from our list of fortunes, encode it into a QByteArray 使用 QDataStream , and then write it to the connecting socket. This is a common way to transfer binary data using QTcpSocket . First we create a QByteArray 和 QDataStream object, passing the bytearray to QDataStream ‘s constructor. We then explicitly set the protocol version of QDataStream to Qt_4_0 to ensure that we can communicate with clients from future versions of Qt (see setVersion() ). We continue by streaming in a random fortune.

QTcpSocket *clientConnection = tcpServer->nextPendingConnection();
connect(clientConnection, &QAbstractSocket::disconnected,
        clientConnection, &QObject::deleteLater);
										

We then call nextPendingConnection() ，其返回 QTcpSocket representing the server side of the connection. By connecting disconnected() to deleteLater() , we ensure that the socket will be deleted after disconnecting.

    clientConnection->write(block);
    clientConnection->disconnectFromHost();
}
										

The encoded fortune is written using write() , and we finally call disconnectFromHost() , which will close the connection after QTcpSocket has finished writing the fortune to the network. Because QTcpSocket works asynchronously, the data will be written after this function returns, and control goes back to Qt’s event loop. The socket will then close, which in turn will cause deleteLater() to delete it.

另请参阅

Fortune 客户端范例 线程化 Fortune 服务器范例

范例工程 @ code.qt.io