WebSocket server example

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.

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

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

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

      m_clients << 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).

  void EchoServer::processTextMessage(QString message)
  {
      QWebSocket *pClient = qobject_cast<QWebSocket *>(sender());
      if (m_debug)
          qDebug() << "Message received:" << message;
      if (pClient) {
          pClient->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.

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

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

  void EchoServer::socketDisconnected()
  {
      QWebSocket *pClient = qobject_cast<QWebSocket *>(sender());
      if (m_debug)
          qDebug() << "socketDisconnected:" << pClient;
      if (pClient) {
          m_clients.removeAll(pClient);
          pClient->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.