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Data object consistency with several workers node

I am trying to create a simple server which will give every new request to different worker. The DATA object is a simple javascript object in separate file. The problem I faced with is CONSISTENCY of this DATA object.
How to prevent worker from handling the request if the previous request is still proceeding? For example first request is UPDATE and lasts longer and the next request is DELETE and proceeds faster What node tool or pattern I need to use to be 100% percent sure that DELETE will happen after UPDATE?
I need to run every worker on a different port
const cluster = require('cluster');
const http = require('http');
const numCPUs = require('os').cpus().length;
cluster.schedulingPolicy = cluster.SCHED_RR;
const PORT = 4000;
if (cluster.isMaster) {
for (let i = 0; i < numCPUs; i++) {
cluster.fork();
}
} else {
http.createServer((req, res) => {
if(req.url === '/users' && req.method === "PUT") {
updateUser(req)
} else if(req.url === '/users' && req.method === "DELETE") {
deleteUser(req)
}
}).listen(PORT++);
}

Each worker must reserve ("lock") the DATA object for exclusive use before it can change it. This can be done by writing a lock file and deleting it again after successful object change.
try {
fs.openSync("path/to/lock/file", "wx+");
/* Change DATA object */
fs.rmSync("path/to/lock/file");
} catch(err) {
if (err.code === "EEXIST") throw "locking conflict";
}
The worker executing the first (UPDATE) request will succeed in writing the lock file, but a concurrent worker executing a second (DELETE) request will experience a locking conflict. It can then either report the failure to the user, or re-try after a short waiting time.
(If you decide to implement the lock in this way, the asynchronous fs methods may be more efficient.)

Your code won't even create multiple servers set aside the different ports, and the PORT variable is a const, so it won't increment either.
What node tool or pattern I need to use to be 100% percent sure that DELETE will happen after UPDATE?
Use some sort of lock, not yet available on JavaScript
Use a semaphore/Mutex variable lock (See code).
Remember, JavaScript is a single-threaded language.
need to run every worker on a different port
For each worker, set the listening based on worker ID (See code). Remember that the CPU cannot have capability to generate workers equal to that of number of cores.
Sample working code:
const express = require('express')
const cluster = require('cluster')
const os = require('os')
if (cluster.isMaster) {
for (let i = 0; i < os.cpus().length; i++) {
cluster.fork()
}
} else {
const app = express()
// Global semaphore/mutex variable isUpdating
var isUpdating = false;
const worker = {
handleRequest(req, res) {
console.log("handleRequest on worker /" + cluster.worker.id);
if (req.method == "GET") { // FOR BROWSER TESTING, CHANGE IT LATER TO PUT
isUpdating = true;
console.log("updateUser GET");
// do updateUser(req);
isUpdating = false;
} else if (req.method == "DELETE") {
if (!isUpdating) { // Check for update lock
console.log("updateUser DELETE");
// do deleteUser(req)
}
}
},
}
app.get('/users', (req, res) => {
worker.handleRequest(req, res)
})
// Now each worker will run on different port
app.listen(4000 + cluster.worker.id, () => {
console.log(`Worker ${cluster.worker.id} started listening on port ${4000 + cluster.worker.id}`)
})
}

Working with multiple tabs with Socket.io

I've the following code working in my server-side, it's all ok. But, I want to keep the same connection between n tabs, because when I open a new tab, looks like I've disconnected from the first tab... So, how can I keep the same connection?
client.js
socket.emit("connected", {user: inputUser.val()};
app.js
var express = require("express"),
app = express(),
http = require("http").Server(app),
io = require("socket.io")(http),
users = {};
io.on("connection", function(socket) {
socket.on("connected", function(data) {
socket.user = data.user;
users[socket.user] = socket;
updateUsers();
});
function updateUsers() {
io.emit("users", Object.keys(users));
}
socket.on("typing", function(data) {
var userMsg = data.user;
if(userMsg in users) {
users[userMsg].emit("typing", {user: socket.user});
}
});
socket.on("disconnect", function(data) {
if(!socket.user) {
return;
}
delete users[socket.user];
updateUsers();
});
});
var port = Number(process.env.PORT || 8000);
http.listen(port, function() {
console.log("Server running on 8000!");
});
Update:
The typing event above works fine... So I tried the typing event according to the answer:
var express = require("express"),
app = express(),
http = require("http").Server(app),
io = require("socket.io")(http),
users = {};
io.on("connection", function(socket) {
socket.on("connected", function(data) {
socket.user = data.user;
// add this socket to the Set of sockets for this user
if (!users[socket.user]) {
users[socket.user] = new Set();
}
users[socket.user].add(socket);
updateUsers();
});
function updateUsers() {
io.emit("users", Object.keys(users));
}
socket.on("typing", function(data) {
var userMsg = data.user;
if(userMsg in users) {
users[userMsg].emit("typing", {user: socket.user});
}
});
socket.on("disconnect", function(data) {
if(!socket.user) {
return;
}
// remove socket for this user
// and remove user if socket count hits zero
if (users[socket.user]) {
users[socket.user].delete(socket);
if (users[socket.user].size === 0) {
delete users[socket.user];
}
}
updateUsers();
});
});
var port = Number(process.env.PORT || 8000);
http.listen(port, function() {
console.log("Server running on 8000!");
});
But it is giving the following error:
users[userMsg].emit("typing", {user: socket.user});
^
TypeError: users[userMsg].emit is not a function
Update²:
To fix the typing event error, I just changed to:
socket.on("typing", function(data) {
var userMsg = data.user;
if(userMsg in users) {
for(let userSet of users[userMsg]) {
userSet.emit("typing", {user: socket.user});
}
}
});

There is no simple way to share a single socket.io connection among multiple tabs in the same browser. The usual model for multiple tabs would be that each tab just has its own socket.io connection.
The opening of a new tab and a new socket.io connection should not, on its own, cause your server to think anything was disconnected. If your code is doing that, then that is a fault in your code and it is probably easier to fix that particular fault.
In fact, if you want to explicitly support multiple tabs and be able to recognize that multiple tabs may all be used by the same user, then you may want to change your server side code so that it can keep track of multiple sockets for a single user, rather than how it is currently coded to only keep track of one socket per user.
If your server code is really just trying to keep track of which users online, then there's probably an easier way to do that by referencing counting each user. I will post a code example in a bit.
var express = require("express"),
app = express(),
http = require("http").Server(app),
io = require("socket.io")(http),
users = {};
io.on("connection", function(socket) {
socket.on("connected", function(data) {
socket.user = data.user;
// increment reference count for this user
if (!users[socket.user]) {
users[socket.user] = 0;
}
++users[socket.user];
updateUsers();
});
function updateUsers() {
io.emit("users", Object.keys(users));
}
socket.on("disconnect", function(data) {
if(!socket.user) {
return;
}
// decrement reference count for this user
// and remove user if reference count hits zero
if (users.hasOwnProperty(socket.user)) {
--users[socket.user];
if (users[socket.user] === 0) {
delete users[socket.user];
}
}
updateUsers();
});
});
var port = Number(process.env.PORT || 8000);
http.listen(port, function() {
console.log("Server running on 8000!");
});
If you need the users object to have the socket object in it, then you can change what is stored in the users object to be a Set of sockets like this:
var express = require("express"),
app = express(),
http = require("http").Server(app),
io = require("socket.io")(http),
users = {};
io.on("connection", function(socket) {
socket.on("connected", function(data) {
socket.user = data.user;
// add this socket to the Set of sockets for this user
if (!users[socket.user]) {
users[socket.user] = new Set();
}
users[socket.user].add(socket);
updateUsers();
});
function updateUsers() {
io.emit("users", Object.keys(users));
}
socket.on("disconnect", function(data) {
if(!socket.user) {
return;
}
// remove socket for this user
// and remove user if socket count hits zero
if (users[socket.user]) {
users[socket.user].delete(socket);
if (users[socket.user].size === 0) {
delete users[socket.user];
}
}
updateUsers();
});
});
var port = Number(process.env.PORT || 8000);
http.listen(port, function() {
console.log("Server running on 8000!");
});

For anyone still having this issue. here is how i fixed it.
let me explain.
once the page refreshes or a new tab is opened, socket dosen't really care so it opens a new connection every time . this is more of a advantage than disadvantage. the best way to tackle the issue is on the server side, once a user logs in with his or her user name , you can send that name along with the query options on the client so it can be used as a unique identifier. in my case i used a token
this.socket = io.connect(`${environment.domain}` , {
query: {token: this.authservice.authToken}
});
then on the server side you can create an empty array to a key and an array of values. the username of the user will be used as a key and the corresponding array of socket as the value. in my own case like i said i used a token
const users = [ ]
socket.nickname = (decoded token username);
users[socket.nickname] = [socket];
then you can perform a simple logic to check if a user already exists in an array, if it does, push the new socket to the array of the user
if ( user.username in users) {
console.log('already exists')
users[user.username].push(socket);
}
if it dosent, just create a new key and add the socket as the key.(make sure its an array because a user can always refresh or open a new tab with the same account and you dont want the chat message to deliver in one tab and not deliver in another)
else {
socket.nickname = username;
users[socket.nickname] = [socket];
}
then to emit a message you simply loop through the array and emit the message accordingly. this way each tab gets the message
socket.on('chat', (data) => {
if (data.to in users) {
for(let i = 0; i < users[data.to].length; i++) {
users[data.to][i].emit('chat', data)
}
for(let i = 0; i < users[data.user].length; i++) {
users[data.user][i].emit('chat', data)
}
}
})
you can add a disconnect logic to remove the socket from the users array too to save memory, so only currently open tabs acre active and closed tabs are removed. i hope it solved your problem

My solution is joining socket to a room with specific user Id.
io.on('connection', async (socket) => {
socket.join('user:' + socket.handshake.headers.uid) // The right way is getting `uid` from cookie/token and verifying user
})
One advantage is sending data to specific user (sending to all tabs)
io.to('user:' + uid).emit('hello');
Hope it's helpful!

I belive the best way is create a channel for the user and unique it by their ID, so, when you need to receive or send something you use the channel and every socket connected to it will receive.

Another solution is to save the flag to localStorage and use eventListener to change localStorage.
Do not connect when another connection exists.
and save message in local storage for send with master tab.

Keep track of connected sockets with socket.io

How do I keep track of all the connected clients in socket.io?
I have tried this on the server:
let numSockets = 0;
io.on('connection', (socket) => {
io.sockets.emit('numSockets', ++numSockets);
socket.on('disconnect', () => {
io.sockets.emit('numSockets', --numSockets);
});
});
and this on the client:
const socket = io();
socket.on('numSockets', function (numSockets) {
console.log(numSockets);
});
It does print a number, but the number, however, if I open 2 windows, it shows 4 connected sockets.
Is this the correct way to do it?
What I want to achieve is to print a list of the connected sockets' ids in a sidebar on my website, and let the user set a username (instead of the automatically generated id) if they want to.
But before moving on to this, I will make sure I can keep track of the sockets in a correct way.

I don't think that io.sockets.emit(io.of('/').connected) is a good idea because it will send a hash of socket objects which is a lot of data :-)
You can try the following function:
function findUsersConnected(room, namespace) {
var names = [];
var ns = io.of(namespace || "/");
if (ns) {
for (var id in ns.connected) {
if(room) {
var roomKeys = Object.keys(ns.connected[id].rooms);
for(var i in roomKeys) {
if(roomKeys[i] == room) {
if (ns.connected[id].username) {
names.push(ns.connected[id].username);
} else {
names.push(ns.connected[id].id);
}
}
}
} else {
if (ns.connected[id].username) {
names.push(ns.connected[id].username);
} else {
names.push(ns.connected[id].id);
}
}
}
}
return names.sort();
}
which returns an array of users connected to a room in a namespace. If a socket has not socket.username property then socket.id is used instead.
For instance:
var usersConnected = findUsersConnected();
var usersConnected = findUsersConnected('myRoom');
var usersConnected = findUsersConnected('myRoom', '/myNamespace');

There's the Namespace#connected object that contains all sockets (keyed by their id) that are connected to a particular namespace.
To retrieve the socket id's of the default namespace (/):
let clientIds = Object.keys( io.of('/').connected );
(where io is the server instance)

As of today, socket.io implemented a function called fetchSockets() on server side to retrieve all sockets that are currently connected on the server-side. (Source : https://socket.io/docs/v4/server-instance/#fetchSockets)
You can then use it like this :
const io = require("socket.io")
async function retrieveSockets() {
const connectedSockets = await io.fetchSockets()
}
As far as i tested, you can even execute action on sockets thanks to that, like emitting events, joinings rooms...etc

const count = io.engine.clientsCount;
This seems like a more inclusive approach and may be the same count of Socket instances in the main namespace as below. But depending on namespaces and usage they could be different.
const count2 = io.of("/").sockets.size;
https://socket.io/docs/v4/server-api/#engineclientscount

I believe it is Object.keys(io.sockets.connected).length. Check server api http://socket.io/docs/server-api/

Why does my websocket close after a few minutes?

I'm using ws with node.js on the server side and the regular WebSocket API on the client side. Opening the connection and messaging a few times back and forth works fine. But the socket always closes after a minute or two. Aren't they supposed to persist? Am I doing something wrong?
My server is node.js hosted on heroku. I just tested locally again using foreman start (the heroku tool to run the server locally) and the socket doesn't close unexpectedly at all, so perhaps it's a misconfiguration on heroku. Anyway, here's a relevant code sample with a few functions omitted for brevity.
I'm testing the application in Chrome on OSX Yosemite but have seen the same behavior in Chrome on Windows 7 when running against production environment.
server:
// Client <-> Host Protocol functions. Move to a different file so that they can be shared.
var C2H_SIGNAL_TYPE_REGISTER = "register";
var H2C_SIGNAL_WELCOME = "welcome";
var H2C_SIGNAL_TYPE_ERROR = "error";
var H2C_SIGNAL_TYPE_PEER_ADDED = "peer_joined";
var H2C_SIGNAL_TYPE_PEER_LEFT = "peer_left";
// Update channel endpoint names.
var UPDATE_ENDPOINT_PEERS = "/peers";
// Create a signal message with all asociated default properties.
// Signal senders should create this object and update it accordingly when
// building a signal message to send to a peer.
function createHostMsg(type)
{
var msg = { signalType: type };
if ( type == H2C_SIGNAL_WELCOME ) {
// Since we're sending a welcome message, we need to provide a list
// of currently connected clients.
msg.peers = {};
for ( var addr in clients ) {
console.log("addr " + addr);
var c = clients[addr].description;
if ( c && c.id ) {
msg.peers[c.id] = c;
}
}
}
return msg;
}
// require modules.
var express = require('express');
var http = require('http');
var bodyParser = require('body-parser');
var multer = require('multer');
// Tracks connected peers.
var clients = { };
// 1. Configure the application context settings.
var app = express();
app.enable('trust proxy');
app.use(express.static(__dirname + '/public'));
app.use(bodyParser.json()); // parse json
app.use(bodyParser.urlencoded({ extended: true })); // for parsing application/x-www-form-urlencoded
app.use(multer()); // for parsing multipart/form-data
// a. configure http routers. these will handle requests coming from app.
app.set('port', (process.env.PORT || 5000));
app.get('/app', peerApp);
app.get('/script/:name', publicScriptRouter);
// 2. Create the http server itself, passing app to be the request handler.
// app will handle routing and multiplexing of incoming requests to different
// route middleware handlers.
var http = require('http');
var WebSocketServer = require("ws").Server
var httpServer = http.createServer(app);
httpServer.listen( app.get('port') );
// 3. Create one of these for all socket endpoints.
var wss = new WebSocketServer( { server: httpServer, path: UPDATE_ENDPOINT_PEERS } );
wss.on("connection", function(webSocket) {
// 1. Associate the socket with the remote address it came from.
var remoteAddress = webSocket._socket.remoteAddress;
var remotePort = webSocket._socket.remotePort;
var clientConnID = remoteAddress + ":" + remotePort;
var exists = clients[clientConnID] != null;
if ( exists ) {
console.log("socket server connection: associating new connection from %s with registered peer.", clientConnID);
clients[clientConnID].socket = webSocket;
} else {
console.log("socket server connection: associating new connection from %s with unregistered peer.", clientConnID);
clients[clientConnID] = { description: null, socket: webSocket };
}
// 2. Hook up handlers for communication over this particular socket.
webSocket.on("message", function(data, flags) {
processMessage(webSocket, data, flags);
});
webSocket.on("close", function() {
// Praise satin for closures!!
removePeer(clientConnID);
});
});
// Transduce the message and handle it accordingly.
function processMessage(socket, data, flags)
{
var msg = JSON.parse(data);
if ( !msg.signalType ) {
var msg = createHostMsg( H2C_SIGNAL_TYPE_ERROR );
msg.errStr = "message_malformed";
socket.send( JSON.stringify( msg ) );
} else if ( msg.signalType == C2H_SIGNAL_TYPE_REGISTER ) {
handleRegistration(socket, msg);
}
}
client:
function initSignalChannel()
{
rtcPeer.channel = new WebSocket( location.origin.replace(/^http/, 'ws') + "/peers" );
rtcPeer.channel.onmessage = updateChannelMessage;
rtcPeer.channel.onopen = function(event) {
console.log("remote socket opened");
}
rtcPeer.channel.onclose = function(event) {
console.log("host closed remote socket.");
}
}
function updateChannelMessage(event) {
var msgObj = JSON.parse(event.data);
if ( !msgObj || !msgObj.signalType ) {
console.log("updateChannelMessage: malformed response!! %o", msgObj );
} else if ( msgObj.signalType == "welcome" ) {
console.log("updateChannelMessage: received welcome from host.");
handleWelcome(msgObj);
} else if ( msgObj.signalType == "peer_joined" ) {
console.log("updateChannelMessage: received peer_joined from host.");
if ( msgObj.peer.id == rtcPeer.description.id ) {
console.log("updateChannelMessage: peer_joined: received notification that I've been added to the room. " + msgObj.peer.id);
console.log(msgObj);
} else {
console.log("updateChannelMessage: peer_joined: peer %s is now online.", msgObj.peer.id);
console.log(msgObj);
addRemotePeer( msgObj.peer );
}
}
}
function addRemotePeer(peerObj)
{
remotePeers[peerObj.id] = peerObj;
var ui = createPeerUIObj(peerObj);
$("#connectedPeerList").append( ui );
}
function createPeerUIObj(peerObj)
{
var ui = null;
if ( peerObj ) {
ui = $("<li></li>");
var a = $("<a></a>");
a.append("peer " + peerObj.id);
ui.append(a);
ui.click(function(event) { console.log("clicked");});
}
return ui;
}
function handleWelcome(msgObj)
{
if ( msgObj.id ) {
console.log("updateChannelMessage: welcome: received id from host. " + msgObj.id);
console.log(msgObj);
rtcPeer.description.id = msgObj.id;
for ( var p in msgObj.peers ) {
addRemotePeer(msgObj.peers[p]);
}
} else {
console.log("updateChannelMessage: malformed response. no id.");
}
}

Thanks for the comments everyone. It turns out that jfriend00 had the right answer, I just didn't realize that the hosting service I was using wouldn't allow for the connection to be kept open.
From the below forum posting, the solution is
you'll need to make your clients ping the server periodically to keep the socket alive.
Not the most ideal situation, but indeed doable. Thanks for pointing me in the right direction.

Duplicate Events Socket.io and Node.js over STOMP

I need some help about my node.js+socket.io implementation.
This service expose a server that connects to an ActiveMQ broker over the STOMP protocol, using the stomp-js node.js module to receive events; that then are displayed in a web front end through websockets using socket.io.
So, everything was fine until I started use the Filters feature of ActiveMQ, but this was not the failure point because of my and my team researching, we found the way to ensure the implementation was fine, the problem comes with the connections: So here's the thing, I receive the filters to subscribe, I successfully subscribe to but when I receive a new set of filters is when comes the duplicated, triplicated and more and more messages depending the number of times that I subscribe-unsubscribe to.
So making some debug, I cannot see what's the problem but I'm almost sure that is some bad implementation of the callbacks or the program flow, I'll attach my code to read your comments about it.
Thanks a lot!
var sys = require('util');
var stomp = require('stomp');
var io = require('socket.io').listen(3000);
var socket = io.sockets.on('connection', function (socket) {
var stomp_args = {
port: 61616,
host: 'IP.ADDRESS',
debug: true,
};
var headers;
var client = new stomp.Stomp(stomp_args);
var setFilters = false;
socket.on('filtros', function (message) {
console.log('DEBUG: Getting filters');
if(setFilters){
client.unsubscribe(headers);
}
else{
client.connect();
}
var selector = '';
headers = '';
for(var attributename in message){
console.log(attributename+" : " + message[attributename]);
if(message[attributename] != ''){
selector += ' ' + attributename + '=\'' + message[attributename] + '\' AND ';
}
}
selector = selector.substring(0, selector.length - 4)
console.log('DEBUG: Selector String: ' + selector);
headers = {
destination: '/topic/virtualtopic',
ack: 'client',
selector: selector
};
if(setFilters)
client.subscribe(headers);
client.on('connected', function() {
client.subscribe(headers);
console.log('DEBUG: Client Connected');
setFilters = true;
});
});
var bufferMessage;
client.on('message', function(message) {
console.log("Got message: " + message.headers['message-id']);
var jsonMessage = JSON.parse(message.body);
if(bufferMessage === jsonMessage){
console.log('DEBUG: recibo un mensaje repetido');
return 0;
}
else{
console.log('DEBUG: Cool');
socket.emit('eventoCajero', jsonMessage);
}
client.ack(message.headers['message-id']);
bufferMessage = jsonMessage;
});
socket.on('disconnect', function(){
console.log('DEBUG: Client disconnected');
if(setFilters){
console.log('DEBUG: Consumer disconnected');
client.disconnect();
}
});
client.on('error', function(error_frame) {
console.log(error_frame.body);
});
});

Looking in the Socket.IO documentation, I've found that this is a known issue (I think critical known issue) and they have not fixed it yet. So, to correct this is necessary to reconnect to the socket in the client side to avoid duplicate messages, using:
socket.socket.reconnect();
function to force reconnection explicitly.