Documentation
Features
Routing Strategies
Tree Tunnel Routing

Tree Tunnel Routing

The Tree Tunnel Routing strategy implements tunneling events, where events flow down through the middleware tree from parent to child nodes.

Implementation 

private async tunnelEvent(event: MiddlewareEvent, node: TreeNode): Promise<void> {
    console.log(`[TreeTunnelRoutingStrategy] Visiting node: ${node.node.name}`);
    await node.node.handleEvent(event); // Current node processes event
    if (!event.handled) {
        for (const child of node.children) {
            await this.tunnelEvent(event, child); // Propagate downward
            if (event.handled) break; // Stop if handled
        }
    }
}

Key Features

  • Automatic Propagation: Events flow automatically from parent to children
  • Early Interception: Parent nodes can handle events before children
  • Propagation Control: Stop event flow by marking as handled
  • Async Support: Full support for asynchronous event handlers

Usage Example 

const router = new TreeTunnelRoutingStrategy();
const parent = new CoreElement();
const child = new CoreElement();

parent.addChild(child);

// Event will tunnel from parent to child
parent.on("init", async (ctx, next) => {
    console.log("Parent initializing");
    await next();
});

child.on("init", async (ctx, next) => {
    console.log("Child initializing");
    await next();
});

// Route an event using tree tunnel strategy
await router.routeEvent(new MiddlewareEvent("init"), parent);

Best Practices

  1. Use for Initialization

    • Perfect for setup and configuration events
    • Parent nodes can initialize before children
    • Ensure proper state propagation

  2. Handle Cancellation

    • Mark events as handled to stop propagation
    • Use for validation or access control
    • Prevent unnecessary processing

  3. Maintain State

    • Use context to pass state down the tree
    • Modify context as needed at each level
    • Keep state changes predictable

XAML Integration 

<TreeGeometry xmlns="http://schemas.codeium.com/middleware/2023">
    <MQTTConnector Name="MQTTConnector" Path=":mqtt" 
                   onInit="handleInit"
                   onIncomingMessage="handleIncomingMessage">
        <JWTAuthorizationComponent Name="JWTAuthorization" 
                                  Path=":jwt" 
                                  onInit="handleAuthInit">
            <TerminalComponent Name="Terminal" 
                             Path=":terminal" 
                             onInit="handleTerminalInit" />
        </JWTAuthorizationComponent>
    </MQTTConnector>
</TreeGeometry>

In this example, the onInit event will tunnel down through the tree, allowing each component to initialize in a parent-first order.

Event Bubbling