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Send continuous updates to connected clients using socket.io and nodejs

Can anyone tell me how to send continuous updates to connected clients every second using nodejs and socket.io?
NOTE: I don't want to use the setInterval() function as it is unfit for my current scenario.

You can do this with setTimeout in a function that references itself in the setTimeout. Basically the same result as doing setInterval but will always wait for the function to finish (assuming synchronous code) before running the timeout function again.
function thingToRepeat() {
let shouldCancel = false;
// send messages, do stuff,
// set shouldCancel to true to stop looping if needed
if (!shouldCancel) {
setTimeout(thingToRepeat, 1000);
}
}

Force a connection to be closed after a period in nodejs

I have user http.request for making connection to another server in nodejs. Unfortunately that server has a delay in responding in some situations. So I want to close the request after some period.
I have found following code but this close connection if target server was not reachable or connection has not been established.
req.on('socket', function (socket) {
socket.setTimeout(myTimeout);
socket.on('timeout', function() {
req.abort();
});
});
What I want is closing connection after for example 2 seconds wether data is coming or not.
Does anyone has any idea?

I don't really know the sockets library you use, maybe it has some ready and nice solution for that as well, but it looks simple to just use setTimeout function:
req.on('socket', function (socket) {
setTimeout(function() {
// maybe some additional condition here
// or recursive call if you want to wait 2 more seconds
// or whatever else
// but if you want to just abort...
req.abort();
}, 2000);
});
Again, this maybe looks like a workaround, but it definitely should be enough as I understand from your request.

Calling socket.disconnect in a forEach loop doesn't actually call disconnect on all sockets

I am new to javascript world. Recently I was working on a chat application in nodejs. So I have a method called gracefulshutdown as follows.
var gracefulShutdown = function() {
logger.info("Received kill signal, shutting down gracefully.");
server.close();
logger.info('Disconnecting all the socket.io clients');
if (Object.keys(io.sockets.sockets).length == 0) process.exit();
var _map = io.sockets.sockets,
_socket;
for (var _k in _map) {
if (_map.hasOwnProperty(_k)) {
_socket = _map[_k];
_socket.disconnect(true);
}
}
...code here...
setTimeout(function() {
logger.error("Could not close connections in time, shutting down");
process.exit();
}, 10 * 1000);
}
Here is what is happening in the disconnect listener.The removeDisconnectedClient method simply updates an entry in the db to indicate the removed client.
socket.on('disconnect', function() {
removeDisconnectedClient(socket);
});
So in this case the disconnect event wasn't fired for all sockets. It was fired for only a few sockets randomly from the array. Although I was able to fix it using setTimeout(fn, 0) with the help of a teammate.
I read about it online and understood only this much that setTimeout defers the execution of of code by adding it to end of event queue. I read about javascript context, call stack, event loop. But I couldn't put together all of it in this context. I really don't understand why and how this issue occurred. Could someone explain it in detail. And what is the best way to solve or avoid them.

It is hard to say for sure without a little more context about the rest of the code in gracefulShutdown but I'm surprised it is disconnecting any of the sockets at all:
_socket = _map[ _k ];
socket.disconnect(true);
It appears that you are assigning an item from _map to the variable _socket but then calling disconnect on socket, which is a different variable. I'm guessing it is a typo and you meant to call disconnect on _socket?
Some of the sockets might be disconnecting for other reasons and the appearance that your loop is disconnecting some but not all the sockets is probably just coincidence.
As far as I can tell from the code you posted, socket should be undefined and you should be getting errors about trying to call the disconnect method on undefined.

From the method name where you use it I can suppose that application exits after attempts to disconnect all sockets. The nature of socket communication is asynchronous, so given you have a decent amount of items in _map it can occur that not all messages with disconnect will be sent before the process exits.
You can increase chances by calling exit after some timeout after disconnecting all sockets. However, why would you manually disconnect? On connection interruption remote sockets will automatically get disconnected...
UPDATE
Socket.io for Node.js doesn't have a callback to know for sure that packet with disconnect command was sent. At least in v0.9. I've debugged that and came to conclusion that without modification of sources it is not possible to catch that moment.
In file "socket.io\lib\transports\websocket\hybi-16.js" a method write is called to send the disconnect packet
WebSocket.prototype.write = function (data) {
...
this.socket.write(buf, 'binary');
...
}
Whereas socket.write is defined in Node.js core transport "nodejs-{your-node-version}-src\core-modules-sources\lib\net.js" as
Socket.prototype.write = function(chunk, encoding, cb)
//cb is a callback to be called on writeRequest complete
However as you see this callback is not provided, so socket.io will not know about the packet having been sent.
At the same time when disconnect() is called for websocket, member disconnected is set to true, and "disconnect" event is broadcasted, indeed. But synchronously. So .on('disconnect' handler on server socket doesn't give and valuable information about whether the packet was sent or not.
Solution
I can make a general conclusion from this. If it is so critical to make sure that all clients are immediately informed (and not wait for a heartbeat timeout or if heartbeat is disabled) then this logic should be implemented manually.
You can send an ordinary message which will mean for the client that server is shutting down and call socket disconnect as soon as the message is received. At the same time server will be able to accept all acknowledgements
Server-side:
var sockets = [];
for (var _k in _map) {
if (_map.hasOwnProperty(_k)) {
sockets.push(_map[_k]);
}
}
sockets.map(function (socket) {
socket.emit('shutdown', function () {
socket.isShutdown = true;
var all = sockets.every(function (skt) {
return skt.isShutdown;
});
if (all) {
//wrap in timeout to let current tick finish before quitting
setTimeout(function () {
process.exit();
});
}
})
})
Clients should behave simply
socket.on('shutdown', function () {
socket.disconnect();
});
Thus we make sure each client has explicitly disconnected. We don't care about server. It will be shutdown shortly.

In the example code it looks like io.sockets.sockets is an Object, however, at least in the library version I am using, it is a mutable array which the socket.io library is free to modify each time you are removing a socket with disconnect(true).
Thus, when you call disconnect(true); if the currently iterated item from index i is removed, this effect like this happens:
var a = [1,2,3,4];
for( var i in a) {
a.splice(i,1); // remove item from array
alert(i);
}
// alerts 0,1
Thus, the disconnect(true) call will ask the socket.io to remove the item from the array - and because you are both holding reference to the same array, the contents of the array are modified during the loop.
The solution is to create a copy of the _map with slice() before the loop:
var _map = io.sockets.sockets.slice(); // copy of the original
It would create a copy of the original array and thus should go through all the items in the array.
The reason why calling setTimeout() would also work is that it would defer the removal of the items from the array, allowing the whole loop iterate without modifying the sockets -Array.

The problem here is that sockjs and socket.io use asynchronous "disconnect" methods. IE. When you call disconnect, it is not immediately terminated. It is just a promise that it WILL be terminated. This has the following effect (assuming 3 sockets)
Your for loop grabs the first socket
The disconnect method is called on the first socket
Your for loop grabs the second socket
The disconnect method is called on the second socket
The disconnect method on the first socket finishes
Your for loop grabs the third socket
The disconnect method is called on the third socket
Program kills itself
Notice, that sockets 2 and 3 haven't necessarily finished yet. This could be for a number of reasons.
Finally, setTimeout(fn, 0) is, as you said, blocking the final call, but it may not be consistent (I haven't dug into this too much). By that I mean, you've set the final termination to be AFTER all your sockets have disconnected. The setTimeout and setInterval methods essentially act more like a queue. Your position in the queue is dictated by the timer you set. Two intervals set for 10s each, where they both run synchronously will cause one to run AFTER the other.

After Socket.io 1.0, the library does not expose you an array of the connected sockets. You can check that io.socket.sockets.length, is not equal to the open socket objects. Your best bet is that you broadcast a 'disconnect' message to all the clients that you want to off, and on.'disconnect' on the client side close the actual WebSocket.

SignalR-Hub after IIS stop,start will no longer call client functions

I have a queue system using SignalR 2.1.1 with Angular. Everything is working perfectly actually. However when I decided to test the system against an IIS outage I noticed a problem. When I stop, then start IIS, IIS restart doesn't cause the issue, my javascript functions that the hub calls will no longer fire. That makes sense to me, but the problem is that the client can still call the server without any issue so the user has no idea they are disconnected. This would certainly mess up my queue state.
So, the solution would seem to be able to test this disconnect somehow and reconnect if necessary. Is there a way to test to see if the client functions my hub is calling are still connected? It seems that since I can call the hub that it should have to reconnect although I don't see any of that activity happening. I've tried the disconnected, reconnecting, stateChanged events on the client side to see if I could catch that happening with no luck.
Thank you for any assistance

So my solution was to create a method on the hub that only responds to the caller:
public void LastChange()
{
Clients.Caller.lastChange();
}
I hooked that call back to this function in my Angular controller:
vm.queueHub.client.lastChange = function onLastChange()
{
vm.lastChangeCalledBack = true;
}
Also in my controller I created this function that tests for the lastChangeCalledBack variable which is set by the function the hub calls. If it's not set after some interval testing I assume we've lost connection:
vm.stillAlive = function()
{
vm.queueHub.server.lastChange();
var found = $interval(function()
{
if (vm.lastChangeCalledBack == true)
{
vm.lastChangeCalledBack = false;
$interval.cancel(found);
}
}, 100, 10);
return found;
}
Finally I created this function in my controller and call it from any functions that make queue changes from the UI and pass in the callback to call if the connection is still valid. For some reason the promise seems to be reverse of what the Angular documentation says, but I must be misunderstanding: $interval docs
function verifyConnection(callback)
{
vm.stillAlive().then(
function (data) {
console.log("Lost connection with server: " + data);
signalrFactory.start();
var reconnectedMessage = "There was a server disconnect. Your connection has been re-established, but you should reload your browser."
getQueue(function () { alert(reconnectedMessage); });
},
function (data) {
console.log("Server connection intact: " + data);
callback();
}
);
}
So for example, this is called from the UI to open a modal:
vm.open = function (item)
{
verifyConnection(function () {
openFlagModal(item);
});
};
I also plan to call the verifyConnection() function periodically as well. This solution seems to work and keep all the clients in sync with the server no matter what. However, I don't like the fact that the SignalR client is already sending pings to the server, and re-establishing the connection, just not reconnecting the callback client methods. It makes me wonder if I'm doing something wrong to cause the client functions to not get reconnected.
Any thoughts on this solution?

Signalr check if hub already started

I have multiple javascript blocks with signalR functions.
I don't know the order of execution so that i want to start the hub with
$.connection.hub.start();
if it isn't started already.
How can i check if the hub is already started? Starting it multiple times it it throws an error.

There are a few ways to approach this problem. The first is to create your own connection status tracking variables, which you set with the connection callback events:
$.connection.hub.start().done(function() { ConnectionStarted = true; })
You can check ConnectionStarted before attempting to start the connection. Unfortunately, this won't work well, as start() is asynchronous and so many instances could try to start a connection before one has finished and set ConnectionStart to true.
So, working solutions. There are two.
First, have every instance use its own connection object (ie: don't use the default $.connection.hub, but instead use manual connection creator:
var localConnection = $.hubConnection();
var localHubProxy= localConnection.createHubProxy('HubNameHere');
This isn't great, as most browsers have a limited number of connections allowed per page, and also because it is generally overkill.
IMO, the best solution is to use the single automatic connection with default proxy ($.connection.hub) and look at the connection state (something I just came across). Each connection object has a state:
$.signalR.connectionState
Object {connecting: 0, connected: 1, reconnecting: 2, disconnected: 4}
So, in each instance, go for something like this?:
if ($.connection.hub && $.connection.hub.state === $.signalR.connectionState.disconnected) {
$.connection.hub.start()
}
Also note that when you create a connection, it will sit in state "disconnected" / 4 until start is called on it. Once start is called, the connection will apparently try to reconnect constantly (if it is interrupted) until $.connection.hub.stop() is called (will then go back to state "disconnected").
Refs:
http://www.asp.net/signalr/overview/hubs-api/hubs-api-guide-javascript-client#establishconnection
https://github.com/SignalR/SignalR/wiki

You can check the connection state in each of your functions like:
function doSomething {
if ($.connection.hub.state === $.signalR.connectionState.disconnected) {
$.connection.hub.start().done(function () { myHub.server.myHubMethod(); });
}
else {
myHub.server.myHubMethod();
}
}

You can detect when the hub has started using .done()
$.connection.hub.start().done(function () {
});
using this method, you can do the following (Taken from docs : https://github.com/SignalR/SignalR/wiki/SignalR-JS-Client-Hubs) you can then keep track of if the connection is open yourself.
function connectionReady() {
alert("Done calling first hub serverside-function");
};
$.connection.hub.start()
.done(function() {
myHub.server.SomeFunction(SomeParam) //e.g. a login or init
.done(connectionReady);
})
.fail(function() {
alert("Could not Connect!");
});