How to attach hooks to connection lifecycle with Fastify WebSocket plugin?

[jhhom]

I'm using Fastify WebSocket plugin (@fastify/websocket) and I want to log a new WebSocket connection, how to do that?

With ws library I can do something like this

import { applyWSSHandler } from '@trpc/server/adapters/ws';
import ws from 'ws';
import { appRouter } from './routers/app';
import { createContext } from './trpc';

const wss = new ws.Server({ port: 3001 });
const handler = applyWSSHandler({ wss, router: appRouter, createContext });

wss.on('connection', (ws) => {
  // HERE I CAN LOG A NEW CONNECTION
  console.log(`➕➕ Connection (${wss.clients.size})`);
  ws.once('close', () => {
    console.log(`➖➖ Connection (${wss.clients.size})`);
  });
});
...

Currently, my code looks like this:

import ws from "@fastify/websocket";
import fastify from "fastify";
import { fastifyTRPCPlugin } from "@trpc/server/adapters/fastify";

const  fastifyServer = fastify({ maxParamLength: 5000 });

const appRouter = t.router({ ... });

fastifyServer.register(ws);
fastifyServer.register(fastifyTRPCPlugin, {
  prefix: "/trpc",
  trpcOptions: { router: appRouter, createContext },
  useWSS: true,
});

I'm not sure how to log a new socket connection when using the fastify websocket plugin, I tried to do something like this:

fastifyServer.websocketServer.on((socket, req) => {
  console.log("new connection")
})

But I'm getting undefined error on accessing fastifyServer.websocketServer, any help is appreciated 🙏