Updating Attributes from ROS2 Messages

Now, we are subscribing to a ROS2 Topic in Java.

We use jrosbridge to connect to the rosbridge websocket and subscribe to a topic. The tutorial example uses the functional interface:

@FunctionalInterface
public interface RosMessageHandler {
    void handle(Message message) throws Exception;
}

A small helper method wraps the subscription:

public void fetchRosMessages(String host, String topic, String type,
                             RosMessageHandler handler) {
    Ros ros = new Ros(host);
    ros.connect();

    Topic echo = new Topic(ros, topic, type);

    echo.subscribe(message -> {
        try {
            handler.handle(message);
        } catch (Exception e) {
            e.printStackTrace();
        }
    });
}

You can test this in isolation:

void ros_topic_test() throws InterruptedException {
    fetchRosMessages("localhost", "/echo", "std_msgs/Int16", message -> {
        System.out.println(message.getMessageType() + ": " + message);
    });

    Thread.sleep(4000);
}

Updating Node Attributes from ROS2 Messages

We now wire ROS2 into the bigraph. Each time a message arrives, we:

Read the integer data field from the JSON message.
Reload the variable space bigraph (/var) from CDO.
Find the Ni node.
Update its attribute key with the new value.
Save the updated model back to CDO.

AtomicBoolean canMatchAgain = new AtomicBoolean(false);

// Subscribe to ROS2 topic
fetchRosMessages("localhost", "/echo", "std_msgs/Int16", message -> {
    JsonObject jsonObject = message.toJsonObject();
    int value = jsonObject.getInt("data");

    // Reload /var from CDO and convert to PureBigraph
    EObject containerOfType = EMFUtils.getRootContainer(
            Objects.requireNonNull(
                    template.find(cdoIdVar, EObject.class, "/var", false)
            )
    );
    PureBigraph bigraphVar = toBigraph(MM, containerOfType, sig());

    // Find Ni node and update attributes
    BigraphEntity.NodeEntity<DynamicControl> Ni = bigraphVar.getNodes().stream()
        .filter(x -> x.getControl().getNamedType().stringValue().equals("Ni"))
        .findFirst()
        .orElseThrow(() -> new RuntimeException("Node 'Ni' not found"));

    Map<String, Object> attributes = Ni.getAttributes();
    attributes.put("key", value);
    System.out.println("New value is = " + attributes.get("key"));

    Ni.setAttributes(attributes);

    // Persist updated var part
    template.save(bigraphVar.getInstanceModel(), "/var");
    canMatchAgain.set(true);
});

At this point, the bigraph acts as a digital shadow of the ROS2 stream: Ni.key always contains the latest integer, which can be access when matching and rewriting the bigraph.

Updating Node Attributes from ROS2 Messages​

Updating Node Attributes from ROS2 Messages