[4.2] Add websocket callbacks

@plotly/dash-websocket-worker/README.md

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+# Dash websocket worker
+
+Worker for websocket based callbacks.

@plotly/dash-websocket-worker/package.json

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+{
+  "name": "@plotly/dash-websocket-worker",
+  "version": "1.0.0",
+  "description": "SharedWorker for WebSocket-based Dash callbacks",
+  "main": "dist/index.js",
+  "types": "dist/index.d.ts",
+  "scripts": {
+    "build": "webpack --mode production",
+    "build:dev": "webpack --mode development",
+    "watch": "webpack --mode development --watch",
+    "clean": "rm -rf dist"
+  },
+  "files": [
+    "dist"
+  ],
+  "keywords": [
+    "dash",
+    "websocket",
+    "sharedworker"
+  ],
+  "author": "Plotly",
+  "license": "MIT",
+  "devDependencies": {
+    "typescript": "^5.0.0",
+    "webpack": "^5.0.0",
+    "webpack-cli": "^5.0.0",
+    "ts-loader": "^9.0.0"
+  }
+}

@plotly/dash-websocket-worker/src/MessageRouter.ts

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+import {
+    WorkerMessageType,
+    WorkerMessage,
+    CallbackRequestMessage,
+    GetPropsResponseMessage,
+    SetPropsMessage,
+    GetPropsRequestMessage,
+    CallbackResponseMessage
+} from './types';
+
+/**
+ * Routes messages between renderers (via MessagePorts) and the WebSocket server.
+ */
+export class MessageRouter {
+    /** Map of renderer IDs to their MessagePorts */
+    private renderers: Map<string, MessagePort> = new Map();
+
+    /** Callback to send messages to the WebSocket server */
+    public sendToServer: ((message: unknown) => void) | null = null;
+
+    /**
+     * Register a renderer with its MessagePort.
+     * @param rendererId Unique identifier for the renderer
+     * @param port The MessagePort for communication
+     */
+    public registerRenderer(rendererId: string, port: MessagePort): void {
+        this.renderers.set(rendererId, port);
+    }
+
+    /**
+     * Unregister a renderer.
+     * @param rendererId The renderer to unregister
+     */
+    public unregisterRenderer(rendererId: string): void {
+        this.renderers.delete(rendererId);
+    }
+
+    /**
+     * Get the number of connected renderers.
+     */
+    public get rendererCount(): number {
+        return this.renderers.size;
+    }
+
+    /**
+     * Handle a message from a renderer.
+     * @param rendererId The ID of the renderer that sent the message
+     * @param message The message from the renderer
+     */
+    public handleRendererMessage(rendererId: string, message: WorkerMessage): void {
+        switch (message.type) {
+            case WorkerMessageType.CALLBACK_REQUEST:
+                this.forwardCallbackRequest(rendererId, message as CallbackRequestMessage);
+                break;
+
+            case WorkerMessageType.GET_PROPS_RESPONSE:
+                this.forwardGetPropsResponse(rendererId, message as GetPropsResponseMessage);
+                break;
+
+            default:
+                console.warn(`Unknown message type from renderer: ${message.type}`);
+        }
+    }
+
+    /**
+     * Handle a message from the WebSocket server.
+     * @param message The message from the server
+     */
+    public handleServerMessage(message: unknown): void {
+        const msg = message as WorkerMessage;
+        const rendererId = msg.rendererId;
+
+        switch (msg.type) {
+            case WorkerMessageType.CALLBACK_RESPONSE:
+                this.forwardToRenderer(rendererId, msg as CallbackResponseMessage);
+                break;
+
+            case WorkerMessageType.SET_PROPS:
+                this.forwardSetProps(rendererId, msg as SetPropsMessage);
+                break;
+
+            case WorkerMessageType.GET_PROPS_REQUEST:
+                this.forwardGetPropsRequest(rendererId, msg as GetPropsRequestMessage);
+                break;
+
+            case WorkerMessageType.ERROR:
+                this.forwardToRenderer(rendererId, msg);
+                break;
+
+            default:
+                console.warn(`Unknown message type from server: ${msg.type}`);
+        }
+    }
+
+    /**
+     * Send a message to all connected renderers.
+     * @param message The message to broadcast
+     */
+    public broadcastToRenderers(message: WorkerMessage): void {
+        for (const [, port] of this.renderers) {
+            port.postMessage(message);
+        }
+    }
+
+    /**
+     * Send a connected notification to a specific renderer.
+     * @param rendererId The renderer to notify
+     */
+    public notifyConnected(rendererId: string): void {
+        const port = this.renderers.get(rendererId);
+        if (port) {
+            port.postMessage({
+                type: WorkerMessageType.CONNECTED,
+                rendererId
+            });
+        }
+    }
+
+    /**
+     * Send a disconnected notification to all renderers.
+     * @param reason Optional reason for disconnection
+     */
+    public notifyDisconnected(reason?: string): void {
+        this.broadcastToRenderers({
+            type: WorkerMessageType.DISCONNECTED,
+            rendererId: '',
+            payload: { reason }
+        });
+    }
+
+    /**
+     * Send an error notification to a specific renderer.
+     * @param rendererId The renderer to notify
+     * @param message Error message
+     * @param code Optional error code
+     */
+    public notifyError(rendererId: string, message: string, code?: string): void {
+        const port = this.renderers.get(rendererId);
+        if (port) {
+            port.postMessage({
+                type: WorkerMessageType.ERROR,
+                rendererId,
+                payload: { message, code }
+            });
+        }
+    }
+
+    private forwardCallbackRequest(rendererId: string, message: CallbackRequestMessage): void {
+        if (this.sendToServer) {
+            this.sendToServer({
+                type: WorkerMessageType.CALLBACK_REQUEST,
+                rendererId,
+                requestId: message.requestId,
+                payload: message.payload
+            });
+        }
+    }
+
+    private forwardGetPropsResponse(rendererId: string, message: GetPropsResponseMessage): void {
+        if (this.sendToServer) {
+            this.sendToServer({
+                type: WorkerMessageType.GET_PROPS_RESPONSE,
+                rendererId,
+                requestId: message.requestId,
+                payload: message.payload
+            });
+        }
+    }
+
+    private forwardToRenderer(rendererId: string, message: WorkerMessage): void {
+        const port = this.renderers.get(rendererId);
+        if (port) {
+            port.postMessage(message);
+        } else {
+            console.warn(`Renderer ${rendererId} not found for message`);
+        }
+    }
+
+    private forwardSetProps(rendererId: string, message: SetPropsMessage): void {
+        this.forwardToRenderer(rendererId, message);
+    }
+
+    private forwardGetPropsRequest(rendererId: string, message: GetPropsRequestMessage): void {
+        this.forwardToRenderer(rendererId, message);
+    }
+}