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Socket.io returning multiple times for one event

Before this is flagged as a duplicate, I have checked the majority of other posts and solutions, to no avail. If anyone wants to double check, here they are:
1) Socket.io Multiple returns for a single event
2) Socket.io message event firing multiple times
3) socket.on event gets triggered multiple times
And many others.
Now to get to the meat of my question!
I have a socket in my client and my server code. Once my server-side socket emits a message, it is received by the client-side socket and prints out the message. With research, this probably ties into event listeners, but I can't find out how to apply it to my code. FYI the following client code is ran when a button is clicked.
Here are snippets of my client code
onButtonClick() {
socket.emit('message_to_server', 'ping');
socket.on('reply', (tmp) => {
console.log(tmp); // in this case, call it 'pong'
this.doSomethingWithMe(tmp);
});
}
doSomethingWithMe(msg) {
// do something with the information
}
The first time I click the button, I receive
> pong
The second time I click the button, I receive
> pong
> pong
It continues to grow exponentially.
I can post my server code if needed, but I'm 100% sure that it emits the information correctly.
Does anyone have any idea for fixing this issue? I can't figure out how the listeners play into this scenario, so I would appreciate any advice!
EDIT: I changed some of my code to the following:
import React ...
const socket = socketIOClient('http://localhost:3000')
socket.on('reply', (tmp) => {
console.log(tmp); // in this case, call it 'pong'
var inst = new drawMe();
inst.doSomethingWithMe(tmp);
});
class drawMe extends Component {
constructor(props) { this.state = { allData: ''}}
onButtonClick() {
...
}
doSomethingWithMe(data) {
this.setState({ allData: data });
}
I am now receiving an error saying that you cannot call setState on a component that is not yet mounted. I probably will not open another question for this issue, but I would appreciate any advice on it. If mods/anyone wants me to close, I have no problem doing so.
EDIT2: If anyone else has this issue, I made it work by moving the code to instantiate the socket and for the event inside my constructor.

You're attaching your event handler again every time the button is clicked. You have socket.on inside the click handler; that method attaches a new handler -- that is, each time it's run, it adds the specified function to the end of the list of functions to run when the event fires. So yes, every time you click the button, you're adding the function to the end of the list and it'll run once for every time it was added. (More accurately, since you're using an anonymous function there, it's creating a new function every time you click the button and adding it to the event handler list to be run when the event fires.)
You should only be attaching event handlers once, for instance just after creating the socket, not on every click.

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?

JavaScript, node.js wait for socket.on response before continuing

I need to get information from the server on the client side.
So on the server side I got this when a client first connect:
socket.on('adduser', function(username){
// misc code, where i set num_player and whatnot
socket.emit('confirmauth', socket.id, socket.num_player, function(data){
console.log(data)
});
// code
}
and on the client side I got this:
var current_player;
socket.on('confirmauth', function(id, username, num, callback) {
current_player = new Player(username,id, num);
console.log(current_player.id); // works
console.log(current_player.num); //works
callback('ok i got it');
});
console.log(current_player.id); //undefined
console.log(current_player.num); //undefined
my problem is that outside of the socket on, the player is not defined. It seems that javascript doesn't wait for my socket on to retrieve data before carrying on.
I tried to wrap socket.on in a $.when done, but it doesn't work. I tried to do a callback, but I think I may not have understood very well how it is supposed to work. So if one of you is willing to help me, I will be grateful
Thank you for your answers.

If you are putting the current_player variable outside of the on callback in an attempt to return it, the alternative is to make your own function receive a callback
function getPlayer(onDone){
socket.on('confirmauth', function(id, username, num, callback) {
var current_player = new Player(username,id, num);
onDone(current_player);
});
}
And instead of doing
var player = getPlayer();
//...
You do
getPlayer(function(player){
//...
});
It kind of sucks that the "callbackyness" is a bit infectious in Javascript but such is life until everyone starts using Generators instead.

This is since socket.on runs taking a callback, and is in the callback where the player is set. however, after calling socket.on you try to read the player, but it is not set, since the callback was not called. Remember you're dealing with asynchronous programming. Try using nibble to chain that code after the callback.
Remember: socket.on and many other socket handlers -and even many other event handles (e.g. jquery)- DON'T wait to the event to happen, so you must think asynchronously.
Take this example:
You call socket.on while the socket is connecting (The connection takes 3 seconds since, e.g., the client is behind Tor). socket.on assigns the event handler (it's the only thing it does since it works for the 11 or more events it has, in the same way).
You access the player.
But the point 1 does not take 3 seconds since it's just an assignment - the connection is what takes 3 seconds to be established. In that sense, you have an undefined (actually: unassigned) variable.

All of these operations are asynchronous, so it's best to avoid global variables and statefulness as much as possible.
That said, have your callback take the newly created Player object to where it needs to go - a register of players, maybe? - and transport it that way.
callback(current_player)
From there, you can put it into a globally available object as you like, for instance if you're using Backbone or have something on the server side keeping track of current users.

Javascript Async.js Parallel not working with socket.io

I have the following block of code:
async.parallel([
function(cb){ module.rpc("user.data",{"username":data.username},cb); },
function(cb){ module.rpc("group.list",{"username":data.username},cb); },
function(cb){ module.rpc("set.list",{},cb); }
],function(error,result){
if(error){ callback(error); return; }
var user = result[0], groups = result[1], sets = result[2];
callback(null,template.render({"user":user,"groups":groups,"sets":sets}));
});
module.rpc is a function that fetches the necessary data from the server via socket.io. Now, the final function (async.parallel's second argument) is supposed to be called only after the given 3 functions have called-back. However, during the template (EJS) rendering, when I try to access groups.data, I sometimes get the error:
Uncaught TypeError: Cannot read property 'data' of undefined
The code seems perfectly fine to me, but works only occasionally. I have reloaded the page repeatedly, without changing the underlying code, and had a success rate of about 20%. I have absolutely no clue why things are going wrong here. All I can guess is that the assignment of that variable is delayed. And so I tried delaying the rendering using window.setTimeout, but to no avail. Why is this happening? How do I fix it?

socket.io keeps sending events to the server repeatedly until it gets an acknowledgement. Depending on the server load, acknowledgements might not be immediate. So multiple identical requests were being sent, and since async.parallel uses a counter instead of individually tracking each function, the final function was getting prematurely called.