Volatile not working from server to client with binary data

Describe the bug Sending a volatile event from the client (Chrome) to Node with binary data works fine. Sending a volatile event from Node to the client with binary data does not work. Sending binary data without volatile works, sending non binary data with volatile works.

To Reproduce

Socket.IO server version: 4.1.1

Server

import { createServer } from "http";
import { Server, Socket } from "socket.io";

const httpServer = createServer({});

const io = new Server(httpServer, {
  cors: {
    origin: "http://localhost:8080",
    methods: ["GET", "POST"],
  },
});

io.on("connection", (socket) => {
  socket.on("some event", (data) => {
    console.log(data);
  });

  setTimeout(() => {
    socket.volatile.emit("some event", "hello");
    // socket.volatile.emit("some event", new ArrayBuffer(10));
  }, 1000);
});

httpServer.listen(3000);

Socket.IO client version: 4.1.1

Client

import { io } from "socket.io-client";

this.socket = io("http://localhost:3000");

    this.socket.on("some event", (data) => {
      console.log(data);
    });

    setTimeout(() => {
      this.socket.volatile.emit("some event", new ArrayBuffer(10));
    }, 1000);

works fine, changing the server code:

  setTimeout(() => {
    // socket.volatile.emit("some event", "hello");
    socket.volatile.emit("some event", new ArrayBuffer(10));
  }, 1000);

and the client receives nothing

Expected behavior The client receives the binary data.

Platform:

• OS: Linux 5.10
• Node 15.14.0

[darrachequesne]

I could indeed reproduce the issue. We will publish a fix as soon as possible.

[darrachequesne]

@brako zut, you are right. This should be finally fixed by https://github.com/socketio/socket.io-adapter/commit/88eee5948aba94f999405239025f29c754a002e2, included in socket.io-adapter@2.3.3 (which should be included by latest socket.io by transitivity).

I added a test case here, to prevent any regression in the future.

Please reopen if needed.