Nodejs networking - realtime communication

Question

I'm new to node.js and I want to ask a simple question about how it works.

I have used FMs in the past for client to client communication and real time applications. For example, for creating a collaborative application where you need to see what other users are doing. I want to explore that using NodeJS.

I have couple of questions:

1) How does NodeJs handle server-to-client communication? Is thee any way to push information to the client? or the client needs to be making requests constantly to the server to see if anything has changed?

2) Is there such thing like permanent connections between the server and the clients?

3) How Can be handle client-to-client communication (of course thru the server)?

Thanks in advance.

Answer 1

3) How Can be handle client-to-client communication (of course thru the server)?

A simple solution is to open a websocket between the server and each client :

[Client A] <==websocket==> [Server] <==websocket==> [Client B]

If you go with Socket.IO for example, it is very easy to do client-to-client communication this way.

When the server receives a message from one client, you just broadcast it to all clients or send it to one specific client depending on your use case.

Some example code using Socket.IO :

var socket = io.listen(server);
socket.on('connection', function(client) {
  client.on('message', function(msg) {
    broadcast(msg); // broadcast message to all clients
    // OR
    socket.clients[session_id].send(msg); // send message to one client
  });

  client.on('disconnect', function( ) {
    console.log('Client Disconnected.');
  });
});