Connected clients in express.io - node.js

Question

I'm developing a simple chat app using node.js and express.io
I would like to display a list of the connected clients (or online for chat) all the time.
In express.io's doc, there is no clear way on how to "get" the list of connected clients once a new one has entered the room, i.e there is just the "broadcast" but not the "get".
Have someone done this before?
Any clues will be really helpful.
Thanks!
Edit:
After trying #jibsales's answer. I think we are almost there. What clients returns me is not the actual array of clients but this one:
[ { id: 'OWix3sqoFZAa20NLk304',
namespace:
{ manager: [Object],
name: '',
sockets: [Object],
auth: false,
flags: [Object],
_events: [Object] },
manager:
{ server: [Object],
namespaces: [Object],
sockets: [Object],
_events: [Object],
settings: [Object],
handshaken: [Object],
connected: [Object],
open: [Object],
closed: [Object],
rooms: [Object],
roomClients: [Object],
oldListeners: [Object],
sequenceNumber: 496205112,
router: [Object],
middleware: [],
route: [Function],
use: [Function],
broadcast: [Function],
room: [Function],
gc: [Object] },
disconnected: false,
ackPackets: 0,
acks: {},
flags: { endpoint: '', room: '' },
readable: true,
store: { store: [Object], id: 'OWix3sqoFZAa20NLk304', data: {} },
_events:
{ error: [Function],
ready: [Function],
connection: [Function],
NewChatPrivateLine: [Function],
NewIdea: [Function],
NewChatLine: [Function],
NewPost: [Function] } } ]
The functions are:
var app = require('express.io')();
app.io.route('connection', function(req) {
req.io.join(req.data.room);
var clients = app.io.sockets.clients(req.data.room);
console.log(clients)
app.io.room(req.data.room).broadcast('announce', {
user: req.data.user,
clients: clients
})
});
This actually returns an error ( data = JSON.stringify(ev); TypeError: Converting circular structure to JSON) as the array has several circular objects and hence it cannot be broadcasted.
Any thoughts?

Answer 1

Because express.io is simply glueing express and socket.io, don't forget to look at socket.io's documentation as well. With that said, since socket.io v0.7, we now have an API method to get this information:
var clients = io.sockets.clients('room'); // all users from room `room`
Unfortunately express.io is written in coffeescript (UGGGH!!!) so I'm having a hard time reading the source, but it looks like when you require the express.io module, the socket.io instance is hoisted up as well:
var express = require('express.io');
var clients = express.io.sockets.clients('room'); // all users from room `room`
If this doesn't work, I would ditch express.io for a manual configuration with express and socket.io because it looks like express.io has a VERY opinionated API. Its really not that hard at all as express.io is doing nothing more than creating a pretty interface/abstraction to manual configuration (which is actually hurting you in this use case if the above doesn't work).
I would also checkout SockJS as I (and many other websocket consumers) ditched socket.io for SockJS due to a lack of community support. Not to mention, there is a SEVERE memory leak in IE9 when falling back to xhr-polling.

Answer 2

Well, finally I went with the "tacking" solution proposed by #Brad. It is not the most elegant but, if you can help me improve it, It'd be awesome!!
This is the final code:
Server-side
var app = require('express.io')();
//To broadcast the users online in room sent by the client
var clients = [];
app.io.route('connect', function (req) {
req.io.leave(req.data.room).on('disconnect', function() {
//To remove client from list when disconnected
var index = clients.indexOf(req.data.user);
if (index > -1) {
clients.splice(index, 1);
}
app.io.room(req.data.room).broadcast('announce', {
user: req.data.user,
clients: clients
})
});
req.io.join(req.data.room);
//To avoid repeating the same client with several opened windows/tabs
var index = clients.indexOf(req.data.user);
if (index === -1) {
clients.push(req.data.user);
}
app.io.room(req.data.room).broadcast('announce', {
user: req.data.user,
clients: clients
})
});
Client-side
// Emit ready event with person name and predefined room for who's online
io.emit('connect', {
room: room,
user: user
});
//Get the signal from server and create your list
io.on('announce', function (data){
//Do awesome stuff with data
});