socket.io - express.js 4 and sockets with express router

Question

I'm trying to create a really simple node API using express.js 4 but I need a few 'realtime' events for which I added socket.io. I'm fairly new to both so I'm likely missing something basic but I can't find good docs/tuts on this.

In the express app (created with the express generator) I have something like this based on simple examples and project docs that I read. This works OK and from client apps, I can send/receive the socket events:

var express = require('express');
var path = require('path');
var logger = require('morgan');
var api = require('./routes/api');
var app = express();
var io = require('socket.io').listen(app.listen(3000));

app.use(logger('dev'));
app.use(express.static(path.join(__dirname, 'public')));
app.use('/api', api);

io.sockets.on('connection', function (socket) {
    console.log('client connect');
    socket.on('echo', function (data) {
        io.sockets.emit('message', data);
    });
});


// error handlers omitted

module.exports = app;

but I want to use the sockets from my API routes (in the ./routes/api.js file that I 'require' above). For example, someone might use the API to PUT/POST a resource and I want that broadcast to connected socket.io clients.

I cannot see how to use the 'io' variable or organise the code currently in the io.sockets.on('connection' ... function inside express routes. Here's the ./routes/api.js file:

var express = require('express');
var router = express.Router();
var io = ???;

router.put('/foo', function(req, res) {
    /* 
      do stuff to update the foo resource 
      ...
     */

    // now broadcast the updated foo..
    io.sockets.emit('update', foo); // how?
});

module.exports = router;

Answer 1

One option is to pass it in to req object.

app.js:

var express = require('express');
var path = require('path');
var logger = require('morgan');
var api = require('./routes/api');
var app = express();
var io = require('socket.io').listen(app.listen(3000));

app.use(logger('dev'));
app.use(express.static(path.join(__dirname, 'public')));

io.sockets.on('connection', function (socket) {
    console.log('client connect');
    socket.on('echo', function (data) {
        io.sockets.emit('message', data);
    });
});

// Make io accessible to our router
app.use(function(req,res,next){
    req.io = io;
    next();
});

app.use('/api', api);

// error handlers omitted

module.exports = app;

./routes/api.js:

var express = require('express');
var router = express.Router();

router.put('/foo', function(req, res) {
    /* 
      do stuff to update the foo resource 
      ...
     */

    // now broadcast the updated foo..
    req.io.sockets.emit('update', foo); 
});

module.exports = router;