Qt 远程对象 - 外部 QIO 设备

描述 Qt 远程对象如何支持自定义 QIODevice 通道。

外部 QIO 设备

Qt 远程对象支持多种通信通道，例如 QTcpServer 和 QTcpSocket 配对。对于所需的 tcp QUrl 或 QLocalServer 和 QLocalSocket 配对的所需名称，需要的监听和连接代码都是样板代码，并由 Qt 内部处理。Qt 远程对象还支持其他类型的 QIODevice，`QRemoteObjectNode` 类提供了额外的帮助来支持需要自定义代码的情况。

以下是一个使用 TCP/IP 的虚构示例。更真实的例子将使用 SSL 连接，这需要配置证书等。

// Create the server and listen outside of QtRO
QTcpServer tcpServer;
tcpServer.listen(QHostAddress(QStringLiteral("127.0.0.1")), 65213);

// Create the host node.  We don't need a hostUrl unless we want to take
// advantage of external schemas (see next example).
QRemoteObjectHost srcNode;

// Make sure any connections are handed to QtRO
QObject::connect(&tcpServer, &QTcpServer::newConnection, &srcNode,
                 [&srcNode, &tcpServer]() {
    srcNode.addHostSideConnection(tcpServer.nextPendingConnection());
});

副本侧代码需要手动连接到主机

QRemoteObjectNode repNode;
QTcpSocket *socket = new QTcpSocket(&repNode);
QObject::connect(socket, &QTcpSocket::connected, &repNode,
        [socket, &repNode]() {
    repNode.addClientSideConnection(socket);
});
socket->connectToHost(QHostAddress(QStringLiteral("127.0.0.1")), 65213);

外部模式

可以创建 QIODevice 的每一侧并调用上述的 `addClientSideConnection(QIODevice *ioDevice)` 和 `addHostSideConnection(QIODevice *ioDevice)`。这是完全支持的，但要求客户端知道如何建立连接或以某种方式发现这些信息。这正是注册表被设计来解决的问题。

Qt 远程对象还允许与注册表一起使用“外部模式”，这有助于连接设置。在 QRemoteObjectHost 侧，用户必须使用所需的模式设置 hostUrl。

// Use standard tcp url for the registry
const QUrl registryUrl = QUrl(QStringLiteral("tcp://127.0.0.1:65212"));
// Use "exttcp" for the "external" interface
const QUrl extUrl = QUrl(QStringLiteral("exttcp://127.0.0.1:65213"));

// Create the server and listen outside of QtRO
QTcpServer tcpServer;
tcpServer.listen(QHostAddress(extUrl.host()), extUrl.port());

// We need a registry for everyone to connect to
QRemoteObjectRegistryHost registry(registryUrl);

// Finally, we create our host node and register "exttcp" as our schema.
// We need the AllowExternalRegistration parameter to prevent the node from
// setting a hostUrlInvalid error.
QRemoteObjectHost srcNode(extUrl, registryUrl, QRemoteObjectHost::AllowExternalRegistration);
// From now on, when we call enableRemoting() from this node, the registry
// will be updated to show the Source object at extUrl.

在 副本 侧，`QRemoteObjectNode` 需要注册一个回调以在检测到外部模式时使用。回调必须是一个 `RemoteObjectSchemaHandler`。

// Use standard tcp url for the registry
const QUrl registryUrl = QUrl(QStringLiteral("tcp://127.0.0.1:65212"));

// This time create the node connected to the registry
QRemoteObjectNode repNode(registryUrl);

// Create the RemoteObjectSchemaHandler callback
QRemoteObjectNode::RemoteObjectSchemaHandler setupTcp = [&repNode](QUrl url) {
    QTcpSocket *socket = new QTcpSocket(&repNode);
    connect(socket, &QTcpSocket::connected,
            [socket, &repNode]() {
        repNode.addClientSideConnection(socket);
    });
    connect(socket, &QSslSocket::errorOccurred,
            [socket](QAbstractSocket::SocketError error) {
        delete socket;
    });
    socket->connectToHost(url.host(), url.port());
};

// Once we call registerExternalSchema, the above method will be called
// whenever the registry sees an object we are interested in on "exttcp"
repNode.registerExternalSchema(QStringLiteral("exttcp"), setupTcp);