Socket.IO在Express 4路由上发出

Question

I'm trying to send messages to my all connected clients with socket.io from express 4 routes. All my routes on same file, it's cloned from official socket.io chat example . I want to emit a "announcement" message to my all recently connected clients.

var app = require('express')();
var http = require('http').Server(app);
var io = require('socket.io')(http);

app.get('/', function(req, res){
  res.sendFile(__dirname + '/index.html');
    io.sockets.emit('chat message', "ANNOUNCEMENT : ..."); // <-- HERE
});

io.on('connection', function(socket){
  socket.on('chat message', function(msg){
    console.log(msg);
    io.emit('chat message', msg);
  });
});

http.listen(3000, function(){
  console.log('listening on *:3000');
});

But it's not emitting message and I don't see anything on console. I've moved my routes to another file and passing io object to route as parameter, but it's still not working. It's working if I emit message from client side JavaScript.

"dependencies": {
    "express": "4.10.2",
    "socket.io": "1.2.0"
  }

Steps to reproduce problem with chat example

1. git clone https://github.com/rauchg/chat-example.git
2. cd chat-example && npm install
3. nano index.js
4. Change content of index.js with my code above
5. node index.js
6. Browse to localhost:3000 , you should see a announcement on chat panel because I'm emitting it on app.get() route. But there is no announcement.

Answer 1

You are emitting to the new page too soon in this:

app.get('/', function(req, res){
    res.sendFile(__dirname + '/index.html');
    io.sockets.emit('chat message', "ANNOUNCEMENT : ..."); // <-- HERE
});

The new page has not yet finished making it's socket.io connection so it won't get the .emit() . In fact, because res.sendFile() is asynchronous, the new page may not have even started making its socket.io connection yet.

You're doing the .emit() as soon as the res.sendFile() is initiated, but if you put console.log() statements into your server code, you will see that that occurs BEFORE the connection arrives. So, you're emitting before the client has actually finished making it's socket.io connection.

If you intend to send something upon page initialization, then you should do it in the server-side io.on('connection', ...) handler because that's where you know the new page is now connected.