CODEWITHSUNDEEP
node.jsexpresswebsocketsocket.ioclient-server
erv
erv

Reputation: 603

I can't get my head around websockets (via socket.io and node.js)

I'm new to websockets/socket.io/node.js. I'm trying to write a card game app, but pretty much all the example tutorials I've found are creating chat applications. So I'm struggling to get my head around the concepts and how they can be applied to my card game.

Keeping it simple, the card game will involve two players. The game involves moving cards around the table. Each player has to see the other player's moves as they happen (hence the need for constant connections). But the opponents cards are concealed to the other.

So two people browse to the same table then click to sit (and play, when both seats are taken). Using 

io.on("connection", function(sock){
      //socket events in here
});

am I creating the one socket ('io', or 'sock'?) that both clients and the server share, or is that two separate sockets (server/clientA and sever/clientB)? I ask, because I'm struggling to understand what's happening when a message is emitted and/or broadcast. If a client emits a message, is that message sent to both the server and the other client, or just the server? And then, further does it also send the message to itself as well?? It seems as though that's the logic... or what is the purpose of the 'broadcast' method?

From a functional perspective, I need the server to send different messages to each player. So it's not like a chatroom where the server sends the chat to everyone. But if it's one socket that the three of us share (clients and server), how do I manage who sees what? I've read about namespaces, but I'm struggling to work out how that could be used. And if it's two separate sockets, then I can more easily imagine sending different data to the separate clients. But how is that implemented - is that two 'io' objects, or two 'sock' objects?

Finally, I've got no idea if this is the sort of long-winded question that is accepted here, so if it's not, can someone direct me to a forum that discussions can occur? Cheers!

(in case it matters I'm also using Expressjs as the server).

Edit to add: Part of my confusion is regarding the difference between 'io' and 'sock'. This code eg from the socket.io page is a good example of methods being applied to either of them:

io.on('connection', function(socket){
  socket.emit('request', /* */); // emit an event to the socket
  io.emit('broadcast', /* */); // emit an event to all connected sockets
  socket.on('reply', function(){ /* */ }); // listen to the event
});

Upvotes: 1

Views: 322

Answers (1)

Jovana
Jovana

Reputation: 380

WebSocket server side listens for incoming socket connections from clients.

Each client upon connection opens its own socket between him and server. The server is the one that keeps track of all clients.

So once client emits the message server is listening for, the server can do with that message whatever. The message itself can contain information about who is the recipient of that message.

The server can pass the message to everyone or broadcast it to specific user or users based on information your client has sent you or some other logic. For a card game:

The server listens for incoming connections. Once two clients are connected both of them should emit game ID in which they want to participate. The server can join their sockets in one game(Room) and all of the communication between those two clients can continue in that room. Each time one of the clients passes data to the server, that data should contain info about the recipient.

Here is one simple example that could maybe get you going: Client side

// set-up a connection between the client and the server
var socket = io.connect();
// get some game identifier
var game = "thebestgameever";
socket.on('connect', function() {
 // Let server know which game you want to play
 socket.emit('game', game);
});
function makeAMove(move)
{
socket.emit('madeAMove', {move:move, game:game});
}

socket.on('move', function(data) {
  console.log('Player made a move', data);
 });

Server side

io = socketio.listen(server);
 //listen for new connections from clients
 io.sockets.on('connection', function(socket) {
// if client joined game get his socket assigned to the game
socket.on('game', function(game) {
    socket.join(game);
});
socket.on('madeAMove', function(data){
  let game = data.game;
  let move = data.move;
  io.sockets.in(game).emit('move', move);
});
})

Upvotes: 1

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