I am creating a browser game with node.js (backend api) and angular (frontend). My goal is to implement an in-game chat to allow communication between players on the same map. The chat is not an essential part of the game, so messages don't need to be instant (few seconds of latency should be ok). It is just a cool feature to talk some times together.
A good solution should be to implement socket.io to have real-time communication. But as chat is not an essential component and is the only thing which will require websockets, i'm wondering if there is not an alternative to avoid server overload with sockets handling.
I thinked about polling every 2 or 3 seconds my REST API to ask for new messages, but it may overload server the same way... What are your recommandations?
Thank you for your advices
There's a pretty cool package called signalhub. It has a nodejs server component and stuff you can use in your users' browsers. It uses a not-so-well-known application of the http (https) protocol called EventSource. EventSource basically opens persistent http (https) connections to a web server.
It's a reliable and lightweight setup. (The README talks about WebRTC signalling, but it's useful for much more than that.)
On the server side, a simple but effective server setup might look like this:
module.exports = function makeHubServer (port) {
const signalhubServer = require('signalhub/server')
const hub = signalhubServer({ maxBroadcasts: 0 })
hub.on('subscribe', function (channel) {
/* you can, but don't have to, keep track of subscriptions here. */
})
hub.on('publish', function (channel, message) {
/* you can, but don't have to, keep track of messages here. */
})
hub.listen(port, null, function () {
const addr = hub.address()
})
return hub
}
In a browser you can do this sort of thing. It user GET to open a persistent EventSource to receive messages. And, when it's time to send a message, it POSTs it.
And, Chromium's devtools Network tab knows all about EventSource connections.
const hub = signalhub('appname', [hubUrl])
...
/* to receive */
hub.subscribe('a-channel-name')
.on('data', message => {
/* Here's a payload */
console.log (message)
})
...
/* to send */
hub.broadcast('a-channel-name', message)
I'm running a chat server using node.js and socket and want to send message to specific client.I use socket.id to send the message to the defined user,like this:
io.sockets.in(user socket.id).emit('message',message)
but there is a problem:
user remains connect but socket id changes rapidly(About once per second) so i can not use socket.id.I tried socket.join(user email) to use user email instead of socket id but after socket id changes it does not work any more.
what's the best way to solve this?session-id?If yes,how?chat application for clients runs on android device.
This is my code:
io.on("connection", function(socket) {
socket.on("login", function(useremail) {
socket.join(useremail);
});
//Here i want to send message to specific user
socket.on('messagedetection', (senderNickname,messageContent,targetuser) => {
//create a message object
let message = {"message":messageContent, "senderNickname":senderNickname}
//targetuser is the email of target user,joined to the socket in login
io.sockets.in(targetuser).emit('message',message)
});
socket.on('disconnect', function() {
console.log( ' user has left ')
socket.broadcast.emit("userdisconnect"," user has left ") });
Making my comment into an answer since it was indeed the issue:
The problem to fix is the rapidly disconnecting/reconnecting clients. That is a clear sign that something in the configuration is not correct.
It could be that network infrastructure is not properly configured to allow long lasting socket.io/webSocket connections. Or, if your system is clustered, it could be caused by non-sticky load balancing.
So, each time the connection is shut-down by the network infrastructure, the client-side socket.io library tries to reconnect creating a new ID for the new connection.
I'm running Debian 8 with NodeJS 6, and are playing around with the IBM Watson IoT platform: https://github.com/ibm-watson-iot/iot-nodejs
I've created a gateway in IBM, and are able to connect and publish data to it with the following code:
var gatewayClient = new iotf.IotfGateway(config);
gatewayClient.connect();
gatewayClient.on('connect', function(){
gatewayClient.publishGatewayEvent("status","json",'{"d" : { "cpu" : 60, "mem" : 50 }}');
});
The config contains unique information regarding my unique gateway.
My challenge is now, that I would like to be able to reuse this gatewayClient in other NodeJS instances. So I'm thinking of something like the following (pseudo-code):
var gatewayClient = new iotf.IotfGateway(config);
gatewayClient.connect();
sharedDatabase-perhaps-Redis[unique-gatewayClient-ID].push(gatewayClient);
And then in any NodeJS on the same server I can call:
sharedDatabase-perhaps-Redis[unique-gatewayClient-ID].publishGatewayEvent("status","json",'{"d" : { "cpu" : 60, "mem" : 50 }}');
I hope it make sense, but I'm a bit confused if it's archivable and how, and if Redis could be a solution or other database-kind-of-thing.
The entire idea is to be able to keep the connection alive/persistant and have clients from different NodeJS instances push data via that one, without creating new connections.
Network connections are not serializable and cannot easily be shared across processes.
Instead, you should consider creating a single "master" process that maintains the connection with the IBM backend, and the clients will communicate with this master instead of with IBM directly (for IoT purposes, a common method of communication is using MQTT).
Also, what stops you from running the code that will be running in those separate Node.js processes in one single process? That would solve the problem too, as each piece of could would be able to use the connection directly.
From what I understand, you already have a single server process that accepts client messages and should relay those messages to the IBM backend. For each unique client, you want to create a new connection to the backend, or re-use a previously created connection.
You could use something like this (error handling withheld for brevity):
// Function to get the connection for a particular client id,
// or, if one doesn't exist yet, create a new one.
let clients = {};
function connectionForClient(uniqueGatewayClientID) {
// Check if we already have a connection for this client.
if (! clients[uniqueGatewayClientID])
// No, create a new one, represented by a promise.
clients[uniqueGatewayClientID] = new Promise(function(resolve) {
let client = new iotf.IotfGateway(config);
client.connect();
client.on('connect', function() {
resolve(client);
});
});
}
return clients[uniqueGatewayClientID];
}
To use:
connectionForClient(uniqueGatewayClientID).then(function(client) {
client.publishGatewayEvent("status","json",'{"d" : { "cpu" : 60, "mem" : 50 }}');
});
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);
});
})
Used
NodeJS, Socket.io
Problem
Imagine there are 2 users U1 & U2, connected to an app via Socket.io. The algorithm is the following:
U1 completely loses Internet connection (ex. switches Internet off)
U2 sends a message to U1.
U1 does not receive the message yet, because the Internet is down
Server detects U1 disconnection by heartbeat timeout
U1 reconnects to socket.io
U1 never receives the message from U2 - it is lost on Step 4 I guess.
Possible explanation
I think I understand why it happens:
on Step 4 Server kills socket instance and the queue of messages to U1 as well
Moreover on Step 5 U1 and Server create new connection (it is not reused), so even if message is still queued, the previous connection is lost anyway.
Need help
How can I prevent this kind of data loss? I have to use hearbeats, because I do not people hang in app forever. Also I must still give a possibility to reconnect, because when I deploy a new version of app I want zero downtime.
P.S. The thing I call "message" is not just a text message I can store in database, but valuable system message, which delivery must be guaranteed, or UI screws up.
Thanks!
Addition 1
I do already have a user account system. Moreover, my application is already complex. Adding offline/online statuses won't help, because I already have this kind of stuff. The problem is different.
Check out step 2. On this step we technically cannot say if U1 goes offline, he just loses connection lets say for 2 seconds, probably because of bad internet. So U2 sends him a message, but U1 doesn't receive it because internet is still down for him (step 3). Step 4 is needed to detect offline users, lets say, the timeout is 60 seconds. Eventually in another 10 seconds internet connection for U1 is up and he reconnects to socket.io. But the message from U2 is lost in space because on server U1 was disconnected by timeout.
That is the problem, I wan't 100% delivery.
Solution
Collect an emit (emit name and data) in {} user, identified by random emitID. Send emit
Confirm the emit on client side (send emit back to server with emitID)
If confirmed - delete object from {} identified by emitID
If user reconnected - check {} for this user and loop through it executing Step 1 for each object in {}
When disconnected or/and connected flush {} for user if necessary
// Server
const pendingEmits = {};
socket.on('reconnection', () => resendAllPendingLimits);
socket.on('confirm', (emitID) => { delete(pendingEmits[emitID]); });
// Client
socket.on('something', () => {
socket.emit('confirm', emitID);
});
Solution 2 (kinda)
Added 1 Feb 2020.
While this is not really a solution for Websockets, someone may still find it handy. We migrated from Websockets to SSE + Ajax. SSE allows you to connect from a client to keep a persistent TCP connection and receive messages from a server in realtime. To send messages from a client to a server - simply use Ajax. There are disadvantages like latency and overhead, but SSE guarantees reliability because it is a TCP connection.
Since we use Express we use this library for SSE https://github.com/dpskvn/express-sse, but you can choose the one that fits you.
SSE is not supported in IE and most Edge versions, so you would need a polyfill: https://github.com/Yaffle/EventSource.
Others have hinted at this in other answers and comments, but the root problem is that Socket.IO is just a delivery mechanism, and you cannot depend on it alone for reliable delivery. The only person who knows for sure that a message has been successfully delivered to the client is the client itself. For this kind of system, I would recommend making the following assertions:
Messages aren't sent directly to clients; instead, they get sent to the server and stored in some kind of data store.
Clients are responsible for asking "what did I miss" when they reconnect, and will query the stored messages in the data store to update their state.
If a message is sent to the server while the recipient client is connected, that message will be sent in real time to the client.
Of course, depending on your application's needs, you can tune pieces of this--for example, you can use, say, a Redis list or sorted set for the messages, and clear them out if you know for a fact a client is up to date.
Here are a couple of examples:
Happy path:
U1 and U2 are both connected to the system.
U2 sends a message to the server that U1 should receive.
The server stores the message in some kind of persistent store, marking it for U1 with some kind of timestamp or sequential ID.
The server sends the message to U1 via Socket.IO.
U1's client confirms (perhaps via a Socket.IO callback) that it received the message.
The server deletes the persisted message from the data store.
Offline path:
U1 looses internet connectivity.
U2 sends a message to the server that U1 should receive.
The server stores the message in some kind of persistent store, marking it for U1 with some kind of timestamp or sequential ID.
The server sends the message to U1 via Socket.IO.
U1's client does not confirm receipt, because they are offline.
Perhaps U2 sends U1 a few more messages; they all get stored in the data store in the same fashion.
When U1 reconnects, it asks the server "The last message I saw was X / I have state X, what did I miss."
The server sends U1 all the messages it missed from the data store based on U1's request
U1's client confirms receipt and the server removes those messages from the data store.
If you absolutely want guaranteed delivery, then it's important to design your system in such a way that being connected doesn't actually matter, and that realtime delivery is simply a bonus; this almost always involves a data store of some kind. As user568109 mentioned in a comment, there are messaging systems that abstract away the storage and delivery of said messages, and it may be worth looking into such a prebuilt solution. (You will likely still have to write the Socket.IO integration yourself.)
If you're not interested in storing the messages in the database, you may be able to get away with storing them in a local array; the server tries to send U1 the message, and stores it in a list of "pending messages" until U1's client confirms that it received it. If the client is offline, then when it comes back it can tell the server "Hey I was disconnected, please send me anything I missed" and the server can iterate through those messages.
Luckily, Socket.IO provides a mechanism that allows a client to "respond" to a message that looks like native JS callbacks. Here is some pseudocode:
// server
pendingMessagesForSocket = [];
function sendMessage(message) {
pendingMessagesForSocket.push(message);
socket.emit('message', message, function() {
pendingMessagesForSocket.remove(message);
}
};
socket.on('reconnection', function(lastKnownMessage) {
// you may want to make sure you resend them in order, or one at a time, etc.
for (message in pendingMessagesForSocket since lastKnownMessage) {
socket.emit('message', message, function() {
pendingMessagesForSocket.remove(message);
}
}
});
// client
socket.on('connection', function() {
if (previouslyConnected) {
socket.emit('reconnection', lastKnownMessage);
} else {
// first connection; any further connections means we disconnected
previouslyConnected = true;
}
});
socket.on('message', function(data, callback) {
// Do something with `data`
lastKnownMessage = data;
callback(); // confirm we received the message
});
This is quite similar to the last suggestion, simply without a persistent data store.
You may also be interested in the concept of event sourcing.
Michelle's answer is pretty much on point, but there are a few other important things to consider. The main question to ask yourself is: "Is there a difference between a user and a socket in my app?" Another way to ask that is "Can each logged in user have more than 1 socket connection at one time?"
In the web world it is probably always a possibility that a single user has multiple socket connections, unless you have specifically put something in place that prevents this. The simplest example of this is if a user has two tabs of the same page open. In these cases you don't care about sending a message/event to the human user just once... you need to send it to each socket instance for that user so that each tab can run it's callbacks to update the ui state. Maybe this isn't a concern for certain applications, but my gut says it would be for most. If this is a concern for you, read on....
To solve this (assuming you are using a database as your persistent storage) you would need 3 tables.
users - which is a 1 to 1 with real people
clients - which represents a "tab" that could have a single connection to a socket server. (any 'user' may have multiple)
messages - a message that needs sent to a client (not a message that needs sent to a user or to a socket)
The users table is optional if your app doesn't require it, but the OP said they have one.
The other thing that needs properly defined is "what is a socket connection?", "When is a socket connection created?", "when is a socket connection reused?". Michelle's psudocode makes it seem like a socket connection can be reused. With Socket.IO, they CANNOT be reused. I've seen be the source of a lot of confusion. There are real life scenarios where Michelle's example does make sense. But I have to imagine those scenarios are rare. What really happens is when a socket connection is lost, that connection, ID, etc will never be reused. So any messages marked for that socket specifically will never be delivered to anyone because when the client who had originally connected, reconnects, they get a completely brand new connection and new ID. This means it's up to you to do something to track clients (rather than sockets or users) across multiple socket connections.
So for a web based example here would be the set of steps I'd recommend:
When a user loads a client (typically a single webpage) that has the potential for creating a socket connection, add a row to the clients database which is linked to their user ID.
When the user actually does connect to the socket server, pass the client ID to the server with the connection request.
The server should validate the user is allowed to connect and the client row in the clients table is available for connection and allow/deny accordingly.
Update the client row with the socket ID generated by Socket.IO.
Send any items in the messages table connected to the client ID. There wouldn't be any on initial connection, but if this was from the client trying to reconnect, there may be some.
Any time a message needs to be sent to that socket, add a row in the messages table which is linked to the client ID you generated (not the socket ID).
Attempt to emit the message and listen for the client with the acknowledgement.
When you get the acknowledgement, delete that item from the messages table.
You may wish to create some logic on the client side that discards duplicate messages sent from the server since this is technically a possibility as some have pointed out.
Then when a client disconnects from the socket server (purposefully or via error), DO NOT delete the client row, just clear out the socket ID at most. This is because that same client could try to reconnect.
When a client tries to reconnect, send the same client ID it sent with the original connection attempt. The server will view this just like an initial connection.
When the client is destroyed (user closes the tab or navigates away), this is when you delete the client row and all messages for this client. This step may be a bit tricky.
Because the last step is tricky (at least it used to be, I haven't done anything like that in a long time), and because there are cases like power loss where the client will disconnect without cleaning up the client row and never tries to reconnect with that same client row - you probably want to have something that runs periodically to cleanup any stale client and message rows. Or, you can just permanently store all clients and messages forever and just mark their state appropriately.
So just to be clear, in cases where one user has two tabs open, you will be adding two identical message to the messages table each marked for a different client because your server needs to know if each client received them, not just each user.
As already written in another answer, I also believe you should look at the realtime as a bonus : the system should be able to work also with no realtime.
I’m developing an enterprise chat for a large company (ios, android, web frontend and .net core + postGres backend) and after having developed a way for the websocket to re-establish connection (through a socket uuid) and get undelivered messages (stored in a queue) I understood there was a better solution: resync via rest API.
Basically I ended up by using websocket just for realtime, with an integer tag on each realtime message (user online, typers, chat message and so on) for monitoring lost messages.
When the client gets an id which is not monolithic (+1) then it understands it is out of sync so it drops all the socket messages and asks a resync of all its observers through REST api.
This way we can handle many variations in the state of the application during the offline period without having to parse tons of websocket messages in a row on reconnection and we are sure to be synced (because the last sync date is set just by the REST api, not from the socket).
The only tricky part is monitoring for realtime messages from the moment you call REST api to the moment the server replies because what is read from the db takes time to get back to the client and in the meanwhile variations could happen so they need to be cached and took into account.
We are going into production in a couple of months,
I hope to get back sleeping by then :)
It is seem that you already have user account system. You know which account is online/offline, you you can handle connect/disconnect event:
So the solution is, add online/offline and offline messages on database for each user:
chatApp.onLogin(function (user) {
user.readOfflineMessage(function (msgs) {
user.sendOfflineMessage(msgs, function (err) {
if (!err) user.clearOfflineMessage();
});
})
});
chatApp.onMessage(function (fromUser, toUser, msg) {
if (user.isOnline()) {
toUser.sendMessage(msg, function (err) {
// alert CAN NOT SEND, RETRY?
});
} else {
toUser.addToOfflineQueue(msg);
}
})
Look here: Handle browser reload socket.io.
I think you could use solution which I came up with. If you modify it properly, it should work as you want.
What I think you want is to have a reusable socket for each user, something like:
Client:
socket.on("msg", function(){
socket.send("msg-conf");
});
Server:
// Add this socket property to all users, with your existing user system
user.socket = {
messages:[],
io:null
}
user.send = function(msg){ // Call this method to send a message
if(this.socket.io){ // this.io will be set to null when dissconnected
// Wait For Confirmation that message was sent.
var hasconf = false;
this.socket.io.on("msg-conf", function(data){
// Expect the client to emit "msg-conf"
hasconf = true;
});
// send the message
this.socket.io.send("msg", msg); // if connected, call socket.io's send method
setTimeout(function(){
if(!hasconf){
this.socket = null; // If the client did not respond, mark them as offline.
this.socket.messages.push(msg); // Add it to the queue
}
}, 60 * 1000); // Make sure this is the same as your timeout.
} else {
this.socket.messages.push(msg); // Otherwise, it's offline. Add it to the message queue
}
}
user.flush = function(){ // Call this when user comes back online
for(var msg in this.socket.messages){ // For every message in the queue, send it.
this.send(msg);
}
}
// Make Sure this runs whenever the user gets logged in/comes online
user.onconnect = function(socket){
this.socket.io = socket; // Set the socket.io socket
this.flush(); // Send all messages that are waiting
}
// Make sure this is called when the user disconnects/logs out
user.disconnect = function(){
self.socket.io = null; // Set the socket to null, so any messages are queued not send.
}
Then the socket queue is preserved between disconnects.
Make sure it saves each users socket property to the database and make the methods part of your user prototype. The database does not matter, just save it however you have been saving your users.
This will avoid the problem mentioned in Additon 1 by requiring a confirmation from the client before marking the message as sent. If you really wanted to, you could give each message an id and have the client send the message id to msg-conf, then check it.
In this example, user is the template user that all users are copied from, or like the user prototype.
Note: This has not been tested.
Been looking at this stuff latterly and think different path might be better.
Try looking at Azure Service bus, ques and topic take care of the off line states.
The message wait for user to come back and then they get the message.
Is a cost to run a queue but its like $0.05 per million operations for a basic queue so cost of dev would be more from hours work need to write a queuing system.
https://azure.microsoft.com/en-us/pricing/details/service-bus/
And azure bus has libraries and examples for PHP, C#, Xarmin, Anjular, Java Script etc.
So server send message and does not need to worry about tracking them.
Client can use message to send back also as means can handle load balancing if needed.
Try this emit chat list
io.on('connect', onConnect);
function onConnect(socket){
// sending to the client
socket.emit('hello', 'can you hear me?', 1, 2, 'abc');
// sending to all clients except sender
socket.broadcast.emit('broadcast', 'hello friends!');
// sending to all clients in 'game' room except sender
socket.to('game').emit('nice game', "let's play a game");
// sending to all clients in 'game1' and/or in 'game2' room, except sender
socket.to('game1').to('game2').emit('nice game', "let's play a game (too)");
// sending to all clients in 'game' room, including sender
io.in('game').emit('big-announcement', 'the game will start soon');
// sending to all clients in namespace 'myNamespace', including sender
io.of('myNamespace').emit('bigger-announcement', 'the tournament will start soon');
// sending to individual socketid (private message)
socket.to(<socketid>).emit('hey', 'I just met you');
// sending with acknowledgement
socket.emit('question', 'do you think so?', function (answer) {});
// sending without compression
socket.compress(false).emit('uncompressed', "that's rough");
// sending a message that might be dropped if the client is not ready to receive messages
socket.volatile.emit('maybe', 'do you really need it?');
// sending to all clients on this node (when using multiple nodes)
io.local.emit('hi', 'my lovely babies');
};