Using await within emit causes payload to be sent to all connected clients

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• report a bug
• request a feature

Current behaviour

Using async/await to construct payloads results in a race condition and messages potentially being broadcast to all connections.

Steps to reproduce

Fiddle: https://github.com/tommoor/socket.io-fiddle/tree/async-await-critical-issue TLDR: Using await within the payload construction for emit will cause the message to be sent to all connections instead of the specific room. eg:

io.to('my-private-room').emit('event', {
  data: await myDatabaseQuery()
});

Expected behaviour

Data should be sent to the correct room and not leaked to all clients.

Setup

• OS: All
• browser: All
• socket.io version: 2.2.0

[ralphpig]

@tommoor Not sure why this issue was highjacked but I’ve been dealing with an issue like this for the past few days.

The problem isn’t with async/await directly. Using async/await will work fine as long as you ensure .emit(..) or .clients(..) isn’t called elsewhere before the Promise resolves. This is because .to(..) doesn’t return a new instance, and .emit(..) and .clients(..) reset Namespace.prototype.rooms, which is set by .to(..).

In your example:

[1, 2, 3].forEach(async () => {
  console.log("sending to private room");
  io.to('my-private-room').emit('event', {
    data: await sleep(100)
  });
});

The call order is:

io.to(roomId)   // rooms: []       -> [roomId]
io.to(roomId)   // rooms: [roomId] -> [roomId]
io.to(roomId)   // rooms: [roomId] -> [roomId]
io.emit(..)     // rooms: [roomId] -> []        Promise resolved
io.emit(..)     // rooms: []       -> []        Promise resolved
io.emit(..)     // rooms: []       -> []        Promise resolved

After the first Promise resolves, io.emit(..) sends to roomId and clears rooms. So subsequents emits send to every socket in the namespace.

The simple fix for this is to move the await before io.to(..) like such:

[1, 2, 3].forEach(async () => {
  console.log("sending to private room");
  let data = await sleep(100);
  io.to('my-private-room').emit('event', {
    data
  });
});

This yields a call order of:

io.to(roomId)   // rooms: []       -> [roomId]  Promise resolved
io.emit(..)     // rooms: [roomId] -> []
io.to(roomId)   // rooms: []       -> [roomId]  Promise resolved
io.emit(..)     // rooms: [roomId] -> []
io.to(roomId)   // rooms: []       -> [roomId]  Promise resolved
io.emit(..)     // rooms: [roomId] -> []

Hope this helps

[quangpl]

Sometime my app has issue : Cannot read property 'emit' of undefined A part of my code :

    socket.on('typing', function (data) {
     
            if (data.to) {
                let strangerSocket1 = io.sockets.sockets[data.to];
                socket.emit('typing', data);
                strangerSocket1.emit('typing', data);
            }
    });

What can I do to resolve this problem ? Thank you !