Problem with namespaces and regex

[ksowa]

Describe the bug
There seems to be a problem with connection callback on the server if the following occur:

1. Server uses dynamic namespaces (e.g. io.of(/^.*$/)...)
2. Server sends a message to the namespace before any client connects to that namespace
3. When at this point client connects to the server, the connection callback is not triggerred

To Reproduce

Socket.IO server version: 4.5.4

Server

import { Server } from "socket.io";

const io = new Server(3000, {
    cors: {
        origin: (origin, callback) => callback(null, origin),
    },
});

io.of(/^.*$/).on('connection', (socket) => {
    console.log('Connected!', socket.id);
});

io.of('testing/namespace').emit('message', 'testing message');

Socket.IO client version: 4.5.4

Client

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

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

socket.on("connect", () => {
  console.log(`connect ${socket.id}`);
});

Expected behavior

The connection callback should be triggered regardless if the first message has been emitted to the namespace before or after any clients connect to that namespace.

Additional context

If we change the server code to the below, it works without any problem.

(first message emitted after first client connects)

const {Server} = require('socket.io');

const io = new Server(3000, {
    cors: {
        origin: (origin, callback) => callback(null, origin),
    },
});

io.of(/^.*$/).on('connection', (socket) => {
    console.log('Connected!', socket.id);
    io.of('testing/namespace').emit('message', 'test');
});

OR (namespace is not dynamic):

const {Server} = require('socket.io');

const io = new Server(3000, {
    cors: {
        origin: (origin, callback) => callback(null, origin),
    },
});

io.of('testing/namespace').on('connection', (socket) => {
    console.log('Connected!', socket.id);
});

io.of('testing/namespace').emit('message', 'test');

OR (client connecting to another namespace):

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

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

socket.on("connect", () => {
  console.log(`connect ${socket.id}`);
});

[darrachequesne]

I could indeed reproduce the issue, thanks. This is a known limitation with dynamic namespaces, any existing static namespaces have the priority over the dynamic ones.

We could maybe fix this by running the regex against any existing namespaces:

io.of('test1');

io.of(/^.*$/); // add test1 as a child of the parent namespace (since it matches the regex)

io.of('test2'); // add test2 as a child of the parent namespace (since it matches the regex)

That might be a surprising behavior for the end users though. What do you think?

Related: #4164

[darrachequesne]

@ksowa this should be fixed by 0d0a7a2, included in version 4.6.1.

A namespace whose name matches the regex of a parent namespace will now be added as a child of this namespace:

const parentNamespace = io.of(/^\/dynamic-\d+$/);

parentNamespace.on("connection", (socket) => {
  console.log(`connection on namespace ${socket.nsp.name}`);
});

And then somewhere else:

io.of("/dynamic-101");

Could you please check?

[ksowa]

@darrachequesne it is indeed fixed in 4.6.1! Thank you for the very fast reaction!

[darrachequesne]

Awesome, thanks for the feedback 👍