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

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.

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

@jyustman

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

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

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

@Frank3K

@Frank3K it is a in-memory adapter, and indeed it should be smth like if (rooms.size !== undefined). However, I have encountered same issue with a redis adapter.

~~So, it must be fixed in multiple places~~

UPD: Nevermind, the redis adapter still relies on the in-memory one

fix(socketio#4645): message emitted to all the rooms, if got `[]` rooms

fix(socket.io-adapter/socketio#4645): message emitted to all the room…

@drmgc

@drmgc the issue is that there is no distinction between no room and an empty room:

Source:

socket.io/packages/socket.io/lib/broadcast-operator.ts

Lines 20 to 27 in 72d61da

    
           constructor( 
        
             private readonly adapter: Adapter, 
        
             private readonly rooms: Set<Room> = new Set<Room>(), 
        
             private readonly exceptRooms: Set<Room> = new Set<Room>(), 
        
             private readonly flags: BroadcastFlags & { 
        
               expectSingleResponse?: boolean; 
        
             } = {}, 
        
           ) {}

@darrachequesne

@darrachequesne yep, I found out already that no rooms is treated as no specific rooms.

I thought it would be a simple one-line fix, but properly introducing a "broadcast to [] rooms" requires changes across quite a few places of this codebase, which I'm not familiar with tbh

Looks like this hasn't been fixed yet. When can we expect a fix for this?

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Empty .to([]) sends to everybody instead of nobody #4645

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	constructor(
	private readonly adapter: Adapter,
	private readonly rooms: Set<Room> = new Set<Room>(),
	private readonly exceptRooms: Set<Room> = new Set<Room>(),
	private readonly flags: BroadcastFlags & {
	expectSingleResponse?: boolean;
	} = {},
	) {}

Empty .to([]) sends to everybody instead of nobody #4645

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Activity

myYang2016 commented on Mar 2, 2023

darrachequesne commented on Mar 3, 2023

inimaz commented on May 9, 2023

Frank3K commented on Dec 28, 2023

drmgc commented on Mar 20, 2025

darrachequesne commented on Mar 28, 2025

drmgc commented on Mar 31, 2025

PrasanthGondi commented on May 10, 2025

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