Websocket on top of express

[MaheshkumarSundaram]

Hi @ralphhanna

I would like to use websocket on top of the express in bpmn-server. As part of workflows, I would like to send messages to clients when necessary.

I did the following changes:

Change 1:

I created a WebSocketServer.ts:

import { WebSocket } from "ws";

export class WebSocketServer {
  private static instance: WebSocket.Server;

  private constructor() {}

  public static getInstance(): WebSocket.Server {
    if (!WebSocketServer.instance) {
      WebSocketServer.instance = new WebSocket.Server({ noServer: true });
    }

    return WebSocketServer.instance;
  }

  public static sendToAllClients(message: string): void {
    const wss = WebSocketServer.getInstance();
    wss.clients.forEach((client) => {
      if (client.readyState === WebSocket.OPEN) {
        client.send(message);
      }
    });
  }
}

Change 2:

I added an upgrade event listener to handle WebSocket upgrade requests on top of Express in app.ts:

import { WebSocketServer } from "./WebSocketServer";

export class WebApp {
 
// OTHER STUFF ALREADY PRESENT

initWebSocket() {
    const server = this.app.listen(this.app.get("port"), () => {
      console.log(
        "App is running at http://localhost:%s in %s mode",
        this.app.get("port"),
        this.app.get("env")
      );
      console.log("  Press CTRL-C to stop\n");
    });

    const wss = WebSocketServer.getInstance();

    server.on("upgrade", (request, socket, head) => {
      // Handle WebSocket upgrade requests
      wss.handleUpgrade(request, socket, head, (ws) => {
        wss.emit("connection", ws, request);
      });
    });
}

  setupExpress() {
    // OTHER STUFF ALREADY PRESENT

    /**
     * Start Express server.
     */
    // app.listen(app.get("port"), () => {
    //   console.log(
    //     "App is running at http://localhost:%s in %s mode",
    //     app.get("port"),
    //     app.get("env")
    //   );
    //   console.log("  Press CTRL-C to stop\n");
    // });

    this.initWebSocket();

    return app;
  }

Change 3:

Then I used the singleton instance of WebSocketServer in appDelegate.ts to use web socket inside Services.

import { WebSocketServer } from "./WebSocketServer";

// OTHER STUFF

class MyServices {
  async TestWebSocket(input, context) {
    WebSocketServer.sendToAllClients(
      "Service Task has been executed successfully!"
    );
  }
}

Websocket starts fine and I tested the connection from client side, it works.

Does my approach have any major pitfalls or vulnerabilities?

If any improvements could eb made, kindly suggest.

Many thanks!

[ralphhanna]

In your app.ts add similar code:

		this.bpmnServer.appDelegate.winSocket = wss;

from your appDelegate, you can now access wss