Qt 远程对象 - 外部 QIODevices¶

描述Qt Remote Objects如何支持自定义QIODevice通道。

外部QIO设备¶

Qt Remote Objects 支持多种开箱即用的通信通道，例如 QTcpServer 和 QTcpSocket 对。给定所需的 TCP QUrl 或所需的名称（对于 QLocalServer 和 QLocalSocket 对），监听和连接所需的代码是样板代码，并由 Qt 内部处理。Qt Remote Objects 还支持其他类型的 QIODevice，并且 QRemoteObjectNode 类提供了额外的方法来支持需要自定义代码的情况。

下面展示了一个人为设计的TCP/IP示例。一个更现实的例子会使用SSL连接，这将需要配置证书等。

// 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());
});

副本端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的每一端并调用addClientSideConnection(QIODevice *ioDevice)和addHostSideConnection(QIODevice *ioDevice)，如上所示。这是完全支持的，但需要客户端知道如何建立连接或有办法发现该信息。这正是注册表设计用来解决的问题。

Qt Remote Objects 还允许在注册表中使用“外部模式”，这有助于连接设置。在 QRemoteObjectHost 端，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Replica端，QRemoteObjectNode需要注册一个回调函数，以便在检测到外部模式时使用。该回调函数必须是一个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);