connection.send behaves differently on Fastify v4

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the regression has not already been reported

Last working version

3.29.0

Other packages

‘@fastify/websocket’: 6.0.1 ‘@fastify/cors’: 8.0.0

Stopped working in version

4.0.0

Node.js version

18.3.0

Operating system

Linux

Operating system version (i.e. 20.04, 11.3, 10)

Fedora 35

💥 Regression Report

I have this simple server:

const fastify = require("fastify")();
fastify.register(require("@fastify/websocket"));
fastify.register(require("@fastify/cors"));

fastify.get("/", { websocket: true }, (connection) => {
  console.log("Someone connected.");

  connection.socket.send("Hello from the server!");

  connection.socket.on("message", (message) => {
    console.log("Server was pinged: ", message.toString());

    connection.socket.send("Hello Fastify WebSockets");
  });
});

fastify.listen({ port: 9000 }, (err, address) => {
  if (err) {
    console.error(err);
    process.exit(1);
  }
  console.log(`Server listening at: ${address}`);
});

I run it using fastify@3.29.0 and it all works. I upgrade to version 4 and when I visit it on the client (http://localhost:9000):

{
  "statusCode": 500,
  "error": "Internal Server Error",
  "message": "connection.socket.send is not a function"
}

Same thing when I go to Postman and I connect via it’s websocket-type request (ws://localhost:9000). It just disconnects.

It seems to have a problem with connection.socket.send("Hello from the server!");. My goal is that i try to send some data from the server upon connection.

This use to work in fastify@3.x.x

Steps to Reproduce

1. Run it using nodemon
2. Observe terminal
3. Connect to ws://localhost:9000 on Postman or connect to Client
4. See no activity.
5. Downgrade fastify to version 3.29.0. Observe success.

Expected Behavior

I expect the server to successfully connect and the fastify route / to start accepting socket messages.

[climba03003]

I think it worth to update the document. Would you like to send a PR to address the issue?

[climba03003]

I see the problem now. You must await the fastify.register(require("@fastify/websocket")).