Empty .to([]) sends to everybody instead of nobody

[jyustman]

Describe the bug io.to([]).emit("hello") sends to everybody instead of nobody

To Reproduce

Socket.IO server version: 4.6.1

Server

import { Server } from "socket.io";

const io = new Server(3000, {});

io.on("connection", () => {
  io.to([]).emit("hello");
});

Socket.IO client version: 4.6.1

Client

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

const socket = io("ws://localhost:3000/", {});

socket.on("hello", () => {
  console.log("hello received");
});

Expected behavior I expect no message to be sent when an empty array is passed to .to().

Platform:

• OS: macOS 13.2

Additional context It's easy to work around, but the behavior was unexpected.

[myYang2016]

I have this problem too, and I have to check every time to see if it's an empty array

[darrachequesne]

@jyustman I could indeed reproduce the behavior, thanks. That is indeed surprising, I guess we can fix this in the next major release.

[inimaz]

I can take a look at this one if that's fine?

[Frank3K]

I observed the same. Could it be due to the following condition in socket.io-adapter?

https://github.com/socketio/socket.io-adapter/blob/28f60b880ad04ff4b48ade0cd529f1970643604f/lib/index.ts#L335-L355