Develop Reference

WebSocket needs browser refresh to update list

My project works as intended except that I have to refresh the browser every time my keyword list sends something to it to display. I assume it's my inexperience with Expressjs and not creating the route correctly within my websocket? Any help would be appreciated.
Browser
let socket = new WebSocket("ws://localhost:3000");
socket.addEventListener('open', function (event) {
console.log('Connected to WS server')
socket.send('Hello Server!');
});
socket.addEventListener('message', function (e) {
const keywordsList = JSON.parse(e.data);
console.log("Received: '" + e.data + "'");
document.getElementById("keywordsList").innerHTML = e.data;
});
socket.onclose = function(code, reason) {
console.log(code, reason, 'disconnected');
}
socket.onerror = error => {
console.error('failed to connect', error);
};
Server
const ws = require('ws');
const express = require('express');
const keywordsList = require('./app');
const app = express();
const port = 3000;
const wsServer = new ws.Server({ noServer: true });
wsServer.on('connection', function connection(socket) {
socket.send(JSON.stringify(keywordsList));
socket.on('message', message => console.log(message));
});
// `server` is a vanilla Node.js HTTP server, so use
// the same ws upgrade process described here:
// https://www.npmjs.com/package/ws#multiple-servers-sharing-a-single-https-server
const server = app.listen(3000);
server.on('upgrade', (request, socket, head) => {
wsServer.handleUpgrade(request, socket, head, socket => {
wsServer.emit('connection', socket, request);
});
});

In answer to "How to Send and/or Stream array data that is being continually updated to a client" as arrived at in comment.
A possible solution using WebSockets may be to
Create an interface on the server for array updates (if you haven't already) that isolates the array object from arbitrary outside modification and supports a callback when updates are made.
Determine the latency allowed for multiple updates to occur without being pushed. The latency should allow reasonable time for previous network traffic to complete without overloading bandwidth unnecessarily.
When an array update occurs, start a timer if not already running for the latency period .
On timer expiry JSON.stringify the array (to take a snapshot), clear the timer running status, and message the client with the JSON text.
A slightly more complicated method to avoid delaying all push operations would be to immediately push single updates unless they occur within a guard period after the most recent push operation. A timer could then push modifications made during the guard period at the end of the guard period.
Broadcasting
The WebSockets API does not directly support broadcasting the same data to multiple clients. Refer to Server Broadcast in ws documentation for an example of sending data to all connected clients using a forEach loop.
Client side listener
In the client-side message listener
document.getElementById("keywordsList").innerHTML = e.data;
would be better as
document.getElementById("keywordsList").textContent = keywordList;
to both present keywords after decoding from JSON and prevent them ever being treated as HTML.

So I finally figured out what I wanted to accomplish. It sounds straight forward after I learned enough and thought about how to structure the back end of my project.
If you have two websockets running and one needs information from the other, you cannot run them side by side. You need to have one encapsulate the other and then call the websocket INSIDE of the other websocket. This can easily cause problems down the road for other projects since now you have one websocket that won't fire until the other is run but for my project it makes perfect sense since it is locally run and needs all the parts working 100 percent in order to be effective. It took me a long time to understand how to structure the code as such.

how to delete messages from a Queue in RabbitMQ immediately after they ve been sent

So I started using RabbitMQ and doing the Tutorials on the Website https://www.rabbitmq.com/tutorials/tutorial-one-javascript.html but i didnt 100% understand how can the aknowledge feature be set so that a Queue will delete the message immediately right after it sends the message, it doesnt matter wether the message will be consumed or not. I'm trying to make a Queue that will delete all the messages right after the sending happens
I tried the examples in the Tutorials for example the hello world example shows that the noAck property is set to true which means we are not acknowledging the messages so the Queue should actually delete those messages after they ve been sent but that's not the case because when i run send.js 3 times and then run receive.js then i ll receive 3 times hello world message which is not what i want
// this is send.js
var amqp = require('amqplib/callback_api');
amqp.connect('amqp://localhost', function(error0, connection) {
if (error0) {
throw error0;
}
connection.createChannel(function(error1, channel) {
if (error1) {
throw error1;
}
var queue = 'hello';
var msg = 'Hello World!';
channel.assertQueue(queue, {
durable: false
});
channel.sendToQueue(queue, Buffer.from(msg));
console.log(" [x] Sent %s", msg);
});
setTimeout(function() {
connection.close();
process.exit(0);
}, 500);
});
// this is receive .js
var amqp = require('amqplib/callback_api');
amqp.connect('amqp://localhost', function(error0, connection) {
if (error0) {
throw error0;
}
connection.createChannel(function(error1, channel) {
if (error1) {
throw error1;
}
var queue = 'hello';
channel.assertQueue(queue, {
durable: false
});
console.log(" [*] Waiting for messages in %s. To exit press CTRL+C",
queue);
channel.consume(queue, function(msg) {
console.log(" [x] Received %s", msg.content.toString());
}, {
noAck: true
});
});
});
for example if i run 3 times send.js there is 2 cases that can happen. case 1 is that the message will be consumed from the receiver and done. case2 is that it ll be not consumed from the receiver and in this case i want it to be deleted i dont want the message to be consumed if i run receive.js after a month from send.js, but i want also my Queue to be durable and not exclusive.
it ll be also a Problem when i keep calling send.js and messages will be pushed all the time in that Queue and then if i run receive.js i ll receive a 1000 message at the same time so my goal is to avoid that.
I appreciate any help

What I think you want, after reading the comments and the question again, is that you want the message be either delivered to the consumer, or dropped if it can't be delivered at the moment it hits the queue. If this is the case, you can set the TTL to 0, either on the queue or on individual messages. From the relevant part of the documentation:
Setting the TTL to 0 causes messages to be expired upon reaching a queue unless they can be delivered to a consumer immediately.
To set the TTL of the queue, in your case of JavaScript client you need to modify the call to channel.assertQueue to include the arguments with x-message-ttl set to 0. Here's the example of the relevant part:
var queue = 'hello';
channel.assertQueue(queue, {
durable: false,
arguments: {
"x-message-ttl": 0
}
});
For more detailed information, consult the amqp.node documentation.

Weird socket.io behavior when Node server is down and then restarted

I implemented a simple chat for my website where users can talk to each other with ExpressJS and Socket.io. I added a simple protection from a ddos attack that can be caused by one person spamming the window like this:
if (RedisClient.get(user).lastMessageDate > currentTime - 1 second) {
return error("Only one message per second is allowed")
} else {
io.emit('message', ...)
RedisClient.set(user).lastMessageDate = new Date()
}
I am testing this with this code:
setInterval(function() {
$('input').val('message ' + Math.random());
$('form').submit();
}, 1);
It works correctly when Node server is always up.
However, things get extremely weird if I turn off the Node server, then run the code above, and start Node server again in a few seconds. Then suddenly, hundreds of messages are inserted into the window and the browser crashes. I assume it is because when Node server is down, socket.io is saving all the client emits, and once it detects Node server is online again, it pushes all of those messages at once asynchronously.
How can I protect against this? And what is exactly happening here?
edit: If I use Node in-memory instead of Redis, this doesn't happen. I am guessing cause servers gets flooded with READs and many READs happen before RedisClient.set(user).lastMessageDate = new Date() finishes. I guess what I need is atomic READ / SET? I am using this module: https://github.com/NodeRedis/node_redis for connecting to Redis from Node.

You are correct that this happens due to queueing up of messages on client and flooding on server.
When the server receives messages, it receives messages all at once, and all of these messages are not synchronous. So, each of the socket.on("message:... events are executed separately, i.e. one socket.on("message... is not related to another and executed separately.
Even if your Redis-Server has a latency of a few ms, these messages are all received at once and everything always goes to the else condition.
You have the following few options.
Use a rate limiter library like this library. This is easy to configure and has multiple configuration options.
If you want to do everything yourself, use a queue on server. This will take up memory on your server, but you'll achieve what you want. Instead of writing every message to server, it is put into a queue. A new queue is created for every new client and delete this queue when processing the last item in queue.
(update) Use multi + watch to create lock so that all other commands except the current one will fail.
the pseudo-code will be something like this.
let queue = {};
let queueHandler = user => {
while(queue.user.length > 0){
// your redis push logic here
}
delete queue.user
}
let pushToQueue = (messageObject) => {
let user = messageObject.user;
if(queue.messageObject.user){
queue.user = [messageObject];
} else {
queue.user.push(messageObject);
}
queueHandler(user);
}
socket.on("message", pushToQueue(message));
UPDATE
Redis supports locking with WATCH which is used with multi. Using this, you can lock a key, and any other commands that try to access that key in thet time fail.
from the redis client README
Using multi you can make sure your modifications run as a transaction,
but you can't be sure you got there first. What if another client
modified a key while you were working with it's data?
To solve this, Redis supports the WATCH command, which is meant to be
used with MULTI:
var redis = require("redis"),
client = redis.createClient({ ... });
client.watch("foo", function( err ){
if(err) throw err;
client.get("foo", function(err, result) {
if(err) throw err;
// Process result
// Heavy and time consuming operation here
client.multi()
.set("foo", "some heavy computation")
.exec(function(err, results) {
/**
* If err is null, it means Redis successfully attempted
* the operation.
*/
if(err) throw err;
/**
* If results === null, it means that a concurrent client
* changed the key while we were processing it and thus
* the execution of the MULTI command was not performed.
*
* NOTICE: Failing an execution of MULTI is not considered
* an error. So you will have err === null and results === null
*/
});
}); });

Perhaps you could extend your client-side code, to prevent data being sent if the socket is disconnected? That way, you prevent the library from queuing messages while the socket is disconnected (ie the server is offline).
This could be achieved by checking to see if socket.connected is true:
// Only allow data to be sent to server when socket is connected
function sendToServer(socket, message, data) {
if(socket.connected) {
socket.send(message, data)
}
}
More information on this can be found at the docs https://socket.io/docs/client-api/#socket-connected
This approach will prevent the built in queuing behaviour in all scenarios where a socket is disconnected, which may not be desirable, however if should protect against the problem you are noting in your question.
Update
Alternatively, you could use a custom middleware on the server to achieve throttling behaviour via socket.io's server API:
/*
Server side code
*/
io.on("connection", function (socket) {
// Add custom throttle middleware to the socket when connected
socket.use(function (packet, next) {
var currentTime = Date.now();
// If socket has previous timestamp, check that enough time has
// lapsed since last message processed
if(socket.lastMessageTimestamp) {
var deltaTime = currentTime - socket.lastMessageTimestamp;
// If not enough time has lapsed, throw an error back to the
// client
if (deltaTime < 1000) {
next(new Error("Only one message per second is allowed"))
return
}
}
// Update the timestamp on the socket, and allow this message to
// be processed
socket.lastMessageTimestamp = currentTime
next()
});
});

How to handle the Storage Queue using the WebJobs

I just started to use Azure as my mobile development as well as my web development.
I am using NodeJs as my framework to work on the azure backend. I am using mobile services and web apps in the azure.
Here is the situation, I am using the Storage Queue from Azure and I am using webjob from my webapps to handle the storage queues. The messages in the queue are going to be sent out to each specific user via notification hub. (Push Notification)
So, the queues will have the size of the 50,000 or more queue messages. All these messages are used to push out the message to the user one by one. However, I tried to handle the queues using WebJob by scheduling 2minutes interval. I know that webjob wont run two instances when the schedule is currently running.
Initially, I wanna use the webjob which run continuously but it will go to pending to restart once the script run finished. My assumption for the continuously running of webjob is that it will run under an endless loop for the script over and over again. until it caught exception or something wrong. My assumption goes wrong, where it will restart by it self once it succeeded the whole script. I know the restart can be adjusted to less than 60seconds but I am not sure whether this helps as I could a lot aysnc operation as well.
For my script, it will run 50,000 or more users messages in the loop. Then, it will send out the push message via Azure nodejs package and then upon return, then it will delete the messages so that it wont appear in the queue anymore. So, there will be some async operation for each loop in the action.
However, everything is working fine but the webjob only have execute maximum of 5 mins and then it will run again on next schedule. Meaning, it will only run to a maximum 5 mins regardless of the operation. I tried with 1,000 messages from the queue and everything works fine but when the messages go up to 5,000 and above, the time is not sufficient. Therefore, some of the async operation is not completed which cause the messages are not deleted.
Is there a way to extend the 5 mins execution time or other better ways to handle the Storage Queues. I looked into the Webjobs SDK but it is only limited to C# and Visual Studio. I am using Mac OSX and Javascript which I could not use.
Please advise as I wasted a lot of time figuring out whats best to handle the storage queue using webjobs but now it seems like it does not serve the purpose when the messages grow bigger and when it dealt with async operation with the total of only 5 mins execution time. I do not have any VM at the moments which I only use PAAS in azure.

According your description:
All these messages are used to push out the message to the user one by one
it will run 50,000 or more users messages in the loop
So your requirement is to send each message in queue to user,and now you get all the messages in queue one time even the message size will get up to more then 50,000, and loop the messages for further operations?
If there is any misunderstanding, feel free to let me know.
In my opinion, cloud you get the top message of the queue at once, and send it to your user, so that it will remarkbly reduce the processing time and which can be set in a continuously webjob. You can refer to How To: Peek at the Next Message to see how to peek at the message in the front of a queue without removing it from the queue
update
As I found you have mentioned that I also have a Web App in Node.js in your whole project architecture.
So I consider whether you can leverage continuous webjob in Web Apps to get one message and send to Notification Hub one time.
And here is my test code snippet:
var azureStorage = require('azure-storage'),
azure = require('azure'),
accountName = '<accountName>',
accountKey = '<accountKey>';
var queueSvc = azureStorage.createQueueService(accountName, accountKey);
var notificationHubService = azure.createNotificationHubService('<notificationhub-name>', '<connectionstring>');
queueSvc.getMessages('myqueue', {numOfMessages:1}, function(error, result, response) {
if (!error) {
// Message text is in messages[0].messagetext
var message = result[0];
console.log(message.messagetext);
var payload = {
data: {
msg: message.messagetext
}
};
notificationHubService.gcm.send(null, payload, function(error) {
if (!error) {
//notification sent
console.log('notification sent');
queueSvc.deleteMessage('myqueue', message.messageid,message.popreceipt,function(error, response) {
if (!error) {
console.log(response);
// Message deleted
} else {
console.log(error);
}
});
}
});
}
});
Details refer to How to use Notification Hubs from Node.js And https://github.com/Azure/azure-storage-node/blob/master/lib/services/queue/queueservice.js#L727
update2
As I get the idea of Service-bus demo on GitHub, I modified the code above, and which greatly improve the efficiency.
Here the code snippet, for your information:
var queueName = 'myqueue';
function checkForMessages(queueSvc, queueName, callback) {
queueSvc.getMessages(queueName, function(err, message) {
if (err) {
if (err === 'No messages to receive') {
console.log('No messages');
} else {
console.log(err);
// callback(err);
}
} else {
callback(null, message[0]);
console.log(message);
}
});
}
function processMessage(queueSvc, err, lockedMsg) {
if (err) {
console.log('Error on Rx: ', err);
} else {
console.log('Rx: ', lockedMsg);
var payload = {
data: {
msg: lockedMsg.messagetext
}
};
notificationHubService.gcm.send(null, payload, function(error) {
if (!error) {
//notification sent
console.log('notification sent');
console.log(lockedMsg)
console.log(lockedMsg.popreceipt)
queueSvc.deleteMessage(queueName, lockedMsg.messageid, lockedMsg.popreceipt, function(err2) {
if (err2) {
console.log('Failed to delete message: ', err2);
} else {
console.log('Deleted message.');
}
})
}
});
}
}
var t = setInterval(checkForMessages.bind(null, queueSvc, queueName, processMessage.bind(null, queueSvc)), 100);
I set the loop time as 100ms in setInterval, now it can process almost 600 message per minutes in my test.

The various configuration settings for WebJobs are explained on this wiki page. In your case you should increase the WEBJOBS_IDLE_TIMEOUT value, which is the time in seconds that a triggered job will timeout if it hasn't produced any output for a period of time. The WEBJOBS_IDLE_TIMEOUT setting needs to be configured in the portal app settings, not via the app.config file.

Socket.io with Cluster: iterating over all open connections

I'm running Socket.io multi-threaded with the native cluster functionality provided by Node.js v0.6.0 and later (with RedisStore).
For every new change in state, the server iterates over each connection and sends a message if appropriate. Note: this isn't "broadcasting" to all connections, it's comparing server data with data the client sent on connection to decide whether to send the server data to that particular client. Consider this code sample:
io.sockets.clients().forEach(function (socket) {
socket.get('subscription', function (err, message) {
if(message.someProperty === someServerData) {
socket.emit('position', someServerData);
}
});
This worked fine when there was only one process, but now, the client receives a message for each Node process (ie. if there are 8 Node process running, all clients receive the messages 8 times).
I understand why the issue arises, but I'm not sure of a fix. How can I assign a 1-to-1 relation from one process to only on client. Perhaps something using NODE_WORKER_ID of Cluster?
This previous SO question seems somewhat related, although I'm not sure it's helpful.
This seems like a pretty common request. Surely, I must be missing something?

So if I get this straight you need to emit custom events from the server. You can do that by creating your own custom EventEmitter and triggering events on that emitter, for example:
var io = require('socket.io').listen(80);
events = require('events'),
customEventEmitter = new events.EventEmitter();
io.sockets.on('connection', function (socket) {
// here you handle what happens on the 'positionUpdate' event
// which will be triggered by the server later on
eventEmitter.on('positionUpdate', function (data) {
// here you have a function that checks if a condition between
// the socket connected and your data set as a param is met
if (condition(data,socket)) {
// send a message to each connected socket
// if the condition is met
socket.emit('the new position is...');
}
});
});
// sometime in the future the server will emit one or more positionUpdate events
customEventEmitter.emit('positionUpdate', data);
Another solution would be to have those users join the 'AWE150', so only they will receive updates for 'AWE150', like so:
var io = require('socket.io').listen(80);
io.sockets.on('connection', function (socket) {
if (client_is_interested_in_AWE) { socket.join('AWE150'); }
io.sockets.in('AWE150').emit('new position here');
});
Resources:
http://spiritconsulting.com.ar/fedex/2010/11/events-with-jquery-nodejs-and-socket-io/