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
});
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);
});
})
Related
I want to make a web app where every user can create a chat room that other users can join. I would like to have a main node server managing the rooms, and every time a user creates a new room, a new chat server should be started by the main server and it should manage the room.
My question is, how can I make the new server start in node.js and how can I manage it?
Socket.io allows you too use the room feature and have the behavior you want (separate chat rooms) without running a separate chat server. Running a separate chat server is not really convenient in node.js because it means running another process, and it makes communication between the main server and the chat servers extra complicated.
What i would advise is using that feature and adopt the following kind of design:
io.on('connection', function(socket) {
//initialize the object representing the client
//Your client has not joined a room yet
socket.on('create_room', function(msg) {
//initalize the object representing the room
//Make the client effectively join that room, using socket.join(room_id)
}
socket.on('join_room', function(msg) {
//If the client is currently in a room, leave it using socket.leave(room_id); I am assuming for the sake of simplicity that a user can only be in a single room at all time
//Then join the new room using socket.join(room_id)
}
socket.on('chat_msg', function(msg) {
//Check if the user is in a room
//If so, send his msg to the room only using socket.broadcast.to(room_id); That way, every socket that have joined the room using socket.join(room_id) will get the message
}
}
With this design, you're simply adding listeners to event, and once set up, the whole server is running fine without having to deal with concurrency or sub processes.
It's still very minimalist and you'll probably want to handle a few more concepts, such as unique nicknames, or password authentication etc.
But that can easily be done using this design.
Have fun experimenting with socket.io and node.js!
I'm working on a Websocket server programmed in Node.js and I'm planning to send out a multicast message to upwards of 20,000 users. The message will be sent out on a regular interval of a second, however I am worried about the performance from the Node.js server.
I understand that Node.js works asynchronously and creates and destroys threads as it requires, but I am unsure of its efficiency. Ideally I would like to send out the message with an average latency of 5ms.
Currently I'm sending out messages to all users through running through a for loop of all the connected clients as following:
function StartBroadcastMessage()
{
console.log("broadcasting socket data to client...!");
for(var i=0;i < clientsWithEvents.length;i++){ //Runs through all the clients
client = clientsWithEvents[i];
if(client.eventid.toLowerCase() == serverEventName.toLowerCase()) //Checks to see if the Client Event names and server names are the same
client.connection.sendUTF(GetEventSocketFeed(client.eventid)); //Sends out event data to that particular client
}
timeoutId = setTimeout(StartBroadcastMessage,2*1000);
}
Is this an efficient way of sending out a multicast message with a low latency, or is there a better way?
Also, is there an efficient way to perform a load test on the server simulating a number of devices connected to the Websocket server? (So far I have found this Node app https://github.com/qarea/websockets-stress-test)
You can use socket.io to broad cast message.
var io = require('socket.io').listen(80);
io.sockets.on('connection', function (socket) {
socket.broadcast.emit('user connected');
});
This will avoid latency(iterating all socket objects and formatting message) in sending individual message to client.
I'm using Socket.IO in my Node Express app, and using the methods described in this excellent post to relate my socket connections and sessions. In a comment the author describes a way to send messages to a particular user (session) like this:
sio.on('connection', function (socket) {
// do all the session stuff
socket.join(socket.handshake.sessionID);
// socket.io will leave the room upon disconnect
});
app.get('/', function (req, res) {
sio.sockets.in(req.sessionID).send('Man, good to see you back!');
});
Seems like a good idea. However, in my app I will often by sending messages to multiple users at once. I'm wondering about the best way to do this in Socket.IO - essentially I need to send messages to multiple rooms with the best performance possible. Any suggestions?
Two options: use socket.io channels or socket.io namespaces. Both are documented on the socket.io website, but in short:
Using channels:
// all on the server
// on connect or message received
socket.join("channel-name");
socket.broadcast.to("channel-name").emit("message to all other users in channel");
// OR independently
io.sockets.in("channel-name").emit("message to all users in channel");
Using namespaces:
// on the client connect to namespace
io.connect("/chat/channel-name")
// on the server receive connections to namespace as normal
// broadcast to namespace
io.of("/chat/channel-name").emit("message to all users in namespace")
Because socket.io is smart enough to not actually open a second socket for additional namespaces, both methods should be comparable in efficiency.
I'm building a simple system like a realtime news feed, using node.js + socket.io.
Since this is a "read-only" system, clients connect and receive data, but clients never actually send any data of their own. The server generates the messages that needs to be sent to all clients, no client generates any messages; yet I do need to broadcast.
The documentation for socket.io's broadcast (end of page) says
To broadcast, simply add a broadcast flag to emit and send method calls. Broadcasting means sending a message to everyone else except for the socket that starts it.
So I currently capture the most recent client to connect, into a variable, then emit() to that socket and broadcast.emit() to that socket, such that this new client gets the new data and all the other clients. But it feels like the client's role here is nothing more than a workaround for what I thought socket.io already supported.
Is there a way to send data to all clients based on an event initiated by the server?
My current approach is roughly:
var socket;
io.sockets.on("connection", function (s) {
socket = s;
});
/* bunch of real logic, yadda yadda ... */
myServerSideNewsFeed.onNewEntry(function (msg) {
socket.emit("msg", { "msg" : msg });
socket.broadcast.emit("msg", { "msg" : msg });
});
Basically the events that cause data to require sending to the client are all server-side, not client-side.
Why not just do like below?
io.sockets.emit('hello',{msg:'abc'});
Since you are emitting events only server side, you should create a custom EventEmitter for your server.
var io = require('socket.io').listen(80);
events = require('events'),
serverEmitter = new events.EventEmitter();
io.sockets.on('connection', function (socket) {
// here you handle what happens on the 'newFeed' event
// which will be triggered by the server later on
serverEmitter.on('newFeed', function (data) {
// this message will be sent to all connected users
socket.emit(data);
});
});
// sometime in the future the server will emit one or more newFeed events
serverEmitter.emit('newFeed', data);
Note: newFeed is just an event example, you can have as many events as you like.
Important
The solution above is better also because in the future you might need to emit certain messages only to some clients, not all (thus need conditions). For something simpler (just emit a message to all clients no matter what), io.sockets.broadcast.emit() is a better fit indeed.
I have a nodejs + socket.io solution and sockets join different rooms. How can i select sockets from different rooms to broadcast to them a certain message without using a for loop that will stall the application for all users?
The solution is simple, make every "special" user (the ones that you want to group) connect to a secret channel with Socket.IO, in your server-side code:
var io = require('socket.io').listen(80);
io.sockets.on('connection', function (socket) {
if (condition_to_determine_is_user_has_access) {
socket.join('specials');
socket.broadcast.to('specials').emit("new special user has joined");
}
});
You may also want to block access to that channel to un-allowed users, based on cookies / sessions.
Read more here: http://www.danielbaulig.de/socket-ioexpress/