socket.io: assure socket joins only one room at a time

Question

I'm working with socket.io 1.3.5. Clients can join rooms by sending a join message. Serverside code:

socket.on('join', function(room) {
  socket.join(room);
});

Now I want to make sure that a client can only be in one room at a time. I want the client to automatically leave the current room if he joins a new one. This is my approach:

function leaveAllRooms(socket) {
    var rooms = socket.adapter.sids[socket.id];
    Object.keys(rooms).forEach(function(room) {
        if (room != socket.id) {
          socket.leave(room);
        }
    });
}

socket.on('join', function(room) {
  leaveAllRooms(socket);
  socket.join(room);
});

Whenever a client want's to join a room, I call leaveAllRooms which calls socket.leave() for all rooms found in socket.adapter.sids[socket.id], except the sockets own room.

This solution seems to be working well, but I'm not sure if it is correct. In another post's comment it is mentioned that io.sockets.manager.roomClients[socket.id] can be used (instead of my socket.adapter.sids[socket.id]). I don't know which one is better. Is there a documentation about this somewhere? I find the docs at socket.io quite sparse.

In addition I wonder if this solution will work with namespaces or even multiple socket.io instances connected via Redis. Any advice?

Answer 1

If you're really just managing to one room at a time from your join message, then you could do this:

socket.on('join', function(room) {
    if (socket.lastRoom) {
        socket.leave(socket.lastRoom);
        socket.lastRoom = null;
    }
    socket.join(room);
    socket.lastRoom = room;
});

It just stores the last room that it was put in as a property on the socket.

This limits a given socket to only one room at a time as processed by your join message. If a client opens more than one socket, then each socket it opens can be in its own room since you haven't tracked this by an authenticated user id, only by socket. I don't understand your multiple instance/redis question since your requirement was that a given socket was only in one room at a time which this implements (a given socket only exists in one place).

---

If you wanted to change the requirements and limit one user to one room at a time and you were using multiple servers and the user could open multiple clients, then you'd have to get a lot more complicated, by storing the last room and server instance centrally in redis so you could enforce policy across multiple servers.