Best Performance - emit to sockets via a loop or rooms

Question

We currently have a chat app whereby when emitting messages out to the appropriate users (could be 1 or several depending how many are in the conversation) we loop through all s

Answer 1

I would use Socket.io rooms to accomplish what you want to do.

Server side, adding a client to a chat room:

socket.join('some room');

Then I would use socket.to('some room').emit for a sender message to be sent to all participants in the room.

Answer 2

First off, socket.io already creates a room for every single user. That room has the name of the socket.id. Rooms are very lightweight objects. They basically just consist of an object with all the ids of the sockets that are in the room. So, there should be no hesitancy to use rooms at all. If they fit the model of what you're doing, then use them.

As for looping yourself vs. emitting to a room, there's really no difference - use whichever makes your code simpler. When you emit to a room, all it does is loop through the sockets in the room and send to each one individually.

Having to loop through the socket connections seems inefficient and I wonder is there a better way.

The main advantage of rooms is that they are pre-built associations of sockets so you don't have to dynamically figure out which sockets you want to send to - there's already a list of sockets in the right room that you can send to. So, it would likely be a small bit more efficient to just send to all sockets in a room than to do what your code is doing because you code is dynamically trying to figure out which sockets to send to, rather than sending to an already made list. Would this make a difference? That depends upon how long the whole list of sockets is and how expensive the computation is to figure out which ones you want to send to. My guess is that it probably wouldn't make much difference either way.

Sending a message to a room is not much more efficient on the actual sending part. Each socket has to be sent the message individually so somebody (your code or the socket.io rooms code) is going to be looping through a list of sockets either way. The underlying OS does not contain a function to send a single message to multiple sockets. Each socket has to be sent to individually.

Then I would just broadcast to the appropriate rooms rather than always looping through all sockets.

Sending to a room is a programming convenience for you, but socket.io will just be looping under the covers anyway.