How to emit event with Socket.io and Node.js?

Question

I find it hard to emit an event because I don't know much about creating an event/emitting an event with socket IO.

Here is my problem on CASE "/publish":

var app = http.createServer(function (req, res) {
    if (req.method == "OPTIONS") {
        res.header('Access-Control-Allow-Origin', '*:*');
        res.send(200);
    } else {

        var u = url.parse(req.url,true),
            body = '';

        req.on('data',function(chunk) {
            body += chunk;
        });

        req.on('end',function() {
            if(body) {
                var data =JSON.parse(body);
                if(data._app_secret && data._app_secret == 'nonexistent') {
                    switch(u.pathname) {
                        case '/generateusersecret' :
                            findTokenByUser(req.headers.host+'_'+data.user_id,function(reply) {
                                if(reply) {
                                    jsonResponse(res,{userSecret : reply});
                                } else {
                                    generateToken(req.headers.host + '_' + data.user_id,data.user_id,res);
                                }
                            });
                        break;
                        case '/getusersecret' :
                            findTokenByUser(req.headers.host + '_' + data.user_id,function(reply) {
                                jsonResponse(res,{userSecret : reply});
                                console.log(reply);
                            });
                        break;
                        case '/publish':
                            if(data.type == 'notification'){
                                var newData = {
                                    item_id : data.item_id,
                                    message : data.message,
                                    recipient : data.channel,
                                    itemLink : data.itemLink,
                                    timestamp : data.timestamp,
                                    read : 0
                                }
                                notification = JSON.stringify(newData);
                                     // I need to emit my event here
                                     Socket.emit(THE EVENT HERE,notification DATA)
                            }

                        break;
                        default: 
                            jsonResponse(res,{error : "Unknown Command: " + u.pathname});
                        break
                    }
                } else {
                    res.writeHead(403, {'Content-Type': 'text/plain'});
                    res.end('Not authorized');
                }
            }
        });
    }
});

app.listen(config.port || 4000, null);

Then I need to listen on:

io.sockets.on('connection'function(socket){
   socket.on('THE EVENT HERE',function(NOTIFICATION DATA){
      //I NEED TO EMIT ANOTHER EVENT HERE
   })
})

Is there a possible way for this? I have to do this because I am using PHP's cURL and I can't emit on client side so I need to emit it on server side.

Solution

It seems you need to emit an event from the server-side, this is possible and the main feature from socket.io.

To broadcast to all connected sockets use this code in the /publish endpoint:

io.sockets.emit('event', data);

Socket.io can also broadcast messages to group of sockets, this feature is called rooms.

If you want to send a message to only one socket, you can mark the sockets with an extra property when they connect and then search those sockets in the list of connected sockets.

---

Complete example:

Server side (server.js):

var http = require('http');
var fs = require('fs');

var server = http.createServer(handler);
var io = require('socket.io').listen(server);

function handler (req, res) {
  if (req.url === '/') {
    return fs.createReadStream(__dirname + '/index.html').pipe(res);
  }
  if (req.url === '/publish' && req.method === 'POST') {

    //this is what you are looking for:
    io.sockets.emit('super event', { message: 'hello' });
    //---------------------------------

    res.writeHead(200, {
      'Location': '/'
    });
    return res.end('');
  }
}

io.sockets.on('connection', function (socket) {
  socket.on('publish', function (data) {
    //if you need to emit to everyone BUT the socket who emit this use:
    //socket.broadcast.emit('super event', data);

    //emit to everyone
    io.sockets.emit('super event', data);
  })
});

server.listen(1080, function () {
  console.log('listening on http://localhost:1080');
});

Client side (index.html):

<html>
<head>
</head>
<body>
    hello world.
    <form action="/publish" method="post">
        <input type="submit" value="send a notification"></input>
    </form>

    <script src="/socket.io/socket.io.js"></script>
    <script>
      var socket = io.connect('/');
      socket.on('super event', function (data) {
        console.log(data);
        alert('got a message!');
      });
    </script>
</body>
</html>

Usage

• Put these two files in one directories.
• npm i socket.io
• node server.js
• open two tabs in the browser pointing to http://localhost:1080
• click the send notification button in one of the tabs

Comments

[NEWBIE]

I tried this code on CASE /publish then added a console.log() on socket connection but it didn't worked..

[José F. Romaniello]

You must be doing something wrong, I added a two files complete example.

[NEWBIE]

Thanks it worked.. how ever can I listen on server side too then emit another event..I mean on.('connection',function(socket){...})

[José F. Romaniello]

yes io.sockets.on('connection', function (socket) { socket.on('event from client', function () { socket.broadcast.emit('super event'); } ) }); ?

[José F. Romaniello]

I added to the example the other case you are looking for.

[NEWBIE]

This code did not worked however I used the app variable to emit an event.. app.emit("myevent",data); ..thank you tho at least I got the Idea from you ..