WebSocket server example

A sample WebSocket server echoing back messages sent to it.

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The Qt Company Ltd.

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Publié le 26 janvier 2024 - Mis à jour le 26 janvier 2024

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Description▲

The echoserver example implements a WebSocket server that echoes back everything that is sent to it.

Code▲

We start by creating a QWebSocketServer (`new QWebSocketServer()`). After the creation, we listen on all local network interfaces (`QHostAddress::Any`) on the specified port.

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EchoServer::EchoServer(quint16 port, bool debug, QObject *parent) :
    QObject(parent),
    m_pWebSocketServer(new QWebSocketServer(QStringLiteral("Echo Server"),
                                            QWebSocketServer::NonSecureMode, this)),
    m_debug(debug)
{
    if (m_pWebSocketServer-&gt;listen(QHostAddress::Any, port)) {
        if (m_debug)
            qDebug() &lt;&lt; "Echoserver listening on port" &lt;&lt; port;
        connect(m_pWebSocketServer, &amp;QWebSocketServer::newConnection,
                this, &amp;EchoServer::onNewConnection);
        connect(m_pWebSocketServer, &amp;QWebSocketServer::closed, this, &amp;EchoServer::closed);
    }
}

If listening is successful, we connect the `newConnection()` signal to the slot `onNewConnection()`. The `newConnection()` signal will be thrown whenever a new WebSocket client is connected to our server.

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void EchoServer::onNewConnection()
{
    QWebSocket *pSocket = m_pWebSocketServer-&gt;nextPendingConnection();

    connect(pSocket, &amp;QWebSocket::textMessageReceived, this, &amp;EchoServer::processTextMessage);
    connect(pSocket, &amp;QWebSocket::binaryMessageReceived, this, &amp;EchoServer::processBinaryMessage);
    connect(pSocket, &amp;QWebSocket::disconnected, this, &amp;EchoServer::socketDisconnected);

    m_clients &lt;&lt; pSocket;
}

When a new connection is received, the client QWebSocket is retrieved (`nextPendingConnection()`), and the signals we are interested in are connected to our slots (`textMessageReceived()`, `binaryMessageReceived()` and `disconnected()`). The client socket is remembered in a list, in case we would like to use it later (in this example, nothing is done with it).

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void EchoServer::processTextMessage(QString message)
{
    QWebSocket *pClient = qobject_cast&lt;QWebSocket *&gt;(sender());
    if (m_debug)
        qDebug() &lt;&lt; "Message received:" &lt;&lt; message;
    if (pClient) {
        pClient-&gt;sendTextMessage(message);
    }
}

Whenever `processTextMessage()` is triggered, we retrieve the sender, and if valid, send back the original message (`sendTextMessage()`). The same is done with binary messages.

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void EchoServer::processBinaryMessage(QByteArray message)
{
    QWebSocket *pClient = qobject_cast&lt;QWebSocket *&gt;(sender());
    if (m_debug)
        qDebug() &lt;&lt; "Binary Message received:" &lt;&lt; message;
    if (pClient) {
        pClient-&gt;sendBinaryMessage(message);
    }
}

The only difference is that the message now is a QByteArray instead of a QString.

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void EchoServer::socketDisconnected()
{
    QWebSocket *pClient = qobject_cast&lt;QWebSocket *&gt;(sender());
    if (m_debug)
        qDebug() &lt;&lt; "socketDisconnected:" &lt;&lt; pClient;
    if (pClient) {
        m_clients.removeAll(pClient);
        pClient-&gt;deleteLater();
    }
}

Whenever a socket is disconnected, we remove it from the clients list and delete the socket. Note: it is best to use `deleteLater()` to delete the socket.

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