Socket.io: Mechanism to add a client to a room with only his ID?

[alexcastano]

I see currently it is possible to send a message to a socket because a default room is created with his ID.

However I don't know if it would be possible to add this socket to a room, to remove from a room or just to disconnect it, of course in multi server environment. Any ideas?

Thank you!

[peteruithoven]

Wait, what are you asking here?

• You can add sockets to rooms
• You can remove sockets from rooms
• In multi server environments you can broadcast to all clients in rooms using socket.io-redis, but you can't (yet) list them.

[alexcastano]

I mean, in a multiserver environment, given a socket id string, I can send a message using:

io.to(string_id).emit('hello')

But I cannot do:

io.join(string_id, room)
io.disconnect_socket(string_id)

Because the socket could be in the current server or maybe in other one.

I hope I've explained better.

[peteruithoven]

What I would do is setup a redis pub/sub channel. Make sure all connected sockets (on all servers) listen to this channel. Then send these kind of commands over this channel.
I wrote the following library to make this slightly easier.
https://www.npmjs.org/package/redis-pubsubber

[alexcastano]

Hello. Thank you for you answer. I see, I could implement it, however I feel like this feature should be implemented by socket.io. Moreover when in the next version you can list the client of a room: https://github.com/Automattic/socket.io/pull/1630

So this is more a feature request if there is not a simple way to do it, a good api to manage clients easily from any server. What do you think?

[rauchg]

Need to think about whether we'll add this feature. I can definitely see the usecase.

[Tug]

I think this could be really handy for implementations where you have a lot of publishers and a few subscribers. In that case most rooms are empty so it's a waste to broadcast to all nodes.
I had a cool optimization in 0.9 where I would do:

if(io.of(nsp).clients(room_id).length > 0) {
    io.of(nsp).in(room_id).emit('m', message);
}

But now that a single node does not see the whole list of clients it cannot be done without some pubsub mechanism to make the publisher join the room on command.

[hekike]

Did you find the right solution how to do this in multi-server env?

I really liked @alexcastano 's approach: io.join(socketId, roomId)

[infnada]

Maybe this can help you https://github.com/socketio/socket.io/issues/2458

[darrachequesne]

Closed by https://github.com/socketio/socket.io-redis/pull/168.

io.adapter.remoteJoin('<my-id>', 'room1', function (err) {
  if (err) { /* unknown id */ }
  // success
});

io.adapter.remoteLeave('<my-id>', 'room1', function (err) {
  if (err) { /* unknown id */ }
  // success
});

[Assdi]

can i do this without redis ? @darrachequesne