I am currently writing an Electron app, for which in the main process I want to talk to a server over websockets.
Part of my main process' code base depends on the user's socket connection status. I require the socket.io-client library
const socket = require('socket.io-client')(host);
which gives me access to the variable socket.connected, which is true or false according to whether a connection is established to the server.
Thus, what I would like is to attach an event emitter to this variable. I have made it to work with polling
var events = require('events').EventEmitter;
var event = new events();
// Emits successfully every 200ms 'Connection: true|false'
event.on('status', function(status){
console.log('Connection: ', status);
});
setInterval(function() {
let status = socket.connected;
event.emit('status', status);
}, 200);
but was wondering whether this truly is the way to implement it. To me it seems strange to have to resort to polling in an async framework like nodejs. On the other, I could not find other ways to implement. Best-case scenario would be to attach somehow an event emitter directly to socket.connected, but was unable to find how to do that. Could anybody advise me on a better way to implement?
Thanks
You can get notified of the completion of a client connection with the connect event:
socket.on('connect', function() {
// client socket is now connected to the server
});
socket.on('disconnect', function() {
// client socket is now disconnected from the server
});
Documentation for client events here: http://socket.io/docs/client-api/#manager(url:string,-opts:object). There are other events in that doc if you also want to see other things like a reconnect.
Related
EDIT: I see that I'm getting ping timeout and transport error reasons in my handler for disconnect on the server. This makes it difficult to maintain state in my server (I'm trying to keep track of which users are connected in a chat-like setup(. I was reading that it may be related to background tabs in Chrome (which I'm running). Does anyone have any experience with these 'spurious' disconnect events?
I'm new to Socket.io and am having some trouble understanding the connection and disconnection process.
As I understand it, the server receives the connection event once when a client connects, and one registers all the handlers for that client in the callback on on.('connection'). Is that true?
I want to maintain an of connected users, so I add a user to that array on the connection handler.
Should I then listen for the disconnect event to know when to remove a user from that array? Can I be guaranteed that that event will only be fired once?
It's a bit confusing, because on the client side, there is the connect event, which apparently can be fired multiple times -- the documentation says
// note: you should register event handlers outside of connect,
// so they are not registered again on reconnection
which is a different paradigm than on the server side, where all the handlers are registered inside the connection handler. But if the client-side connect event can fire on re-connection, what is the reconnect event for? (The docs says this event is "Fired upon a successful reconnection.")
In general I'm confused about the process of connection, disconnection and re-connection and how this relates to events, whether it happens "randomly" due to connection issues or only under the programmer's control, and how many times one should anticipate receiving each of these events -- once only for server, multiple times for client?
Thanks for any help!
I'm new to Socket.io and am having some trouble understanding the
connection and disconnection process.
Welcome to the wonderful world of Node.js + Socket.io It's super powerful!
As I understand it, the server receives the connection event once when
a client connects, and one registers all the handlers for that client
in the callback on on.('connection'). Is that true?
Correct. Take a look at this example of my code:
Server-side
var clients = []; /* stores all sockets on the fly */
io.on('connection', function (socket) {
clients[socket.id] = socket; /* keeps an array of sockets currently connected */
socket.on('disconnect', function (data) {
console.log(socket.id + " disconnected");
delete clients[socket.id];
});
});
Client-side
socket = io.connect(YOUR_SOCKET_URI, { transports: ['websocket'] } );
socket_delegates();
socket_delegates = function() {
// Socket events
socket.on('connect', function(data) {
/* handle on connect events */
});
socket.on('disconnect', function () {
/* handle disconnect events - possibly reconnect? */
});
socket.on('reconnect', function () {
/* handle reconnect events */
});
socket.on('reconnect_error', function () {
/* handle reconnect error events - possible retry? */
});
}
Should I then listen for the disconnect event to know when to remove a
user from that array? Can I be guaranteed that that event will only be
fired once?
Yes. You will see in the above server code that we listen for disconnect and then do what we need to.
Nothing should be random. You should have code in place to handle the connect, disconnect on the server side and code to handle the connect, disconnect and reconnect on the client side.
I have a node.js script which allows a client to connect and receive some realtime data from an external script.
I have just upgraded node.js & socket.io to the current versions (from <0.9) and am trying to get to grips with what happens when a client quits, times out or disconnects from the server.
Here is my current node.js script;
var options = {
allowUpgrades: true,
pingTimeout: 50000,
pingInterval: 25000,
cookie: 'k1'
};
var io = require('socket.io')(8002, options);
cp = require('child_process');
var tail = cp.spawn('test-scripts/k1.rb');
//On connection do the code below//
io.on('connection', function(socket) {
console.log('************ new client connected ****************', io.engine.clientsCount);
//Read from mongodb//
var connection_string = '127.0.0.1:27017/k1-test';
var mongojs = require('mongojs');
var db = mongojs(connection_string, ['k1']);
var k1 = db.collection('k1');
db.k1.find({}, {'_id': 0, "data.time":0}).forEach(function(err, doc) {
if (err) throw err;
if (doc) { socket.emit('k1', doc); }
});
//Run Ruby script & Listen to STDOUT//
tail.stdout.on('data', function(chunk) {
var closer = chunk.toString()
var sampArray = closer.split('\n');
for (var i = 0; i < sampArray.length; i++) {
try {
var newObj = JSON.parse(sampArray[i]);
// DO SOCKET //
socket.emit('k1', newObj);
} catch (err) {}
}
});
socket.on('disconnect', function(){
console.log('****************** user disconnected *******************', socket.id, io.engine.clientsCount);
socket.disconnect();
});
});
In the old version of socket.io when a client exits I get the following logged in debug;
info - transport end (undefined)
debug - set close timeout for client Owb_B6I0ZEIXf6vOF_b-
debug - cleared close timeout for client Owb_B6I0ZEIXf6vOF_b-
debug - cleared heartbeat interval for client Owb_B6I0ZEIXf6vOF_b-
debug - discarding transport
then everything goes quite and all is well.
With the new (1.3.7) version of socket.io when a client exits I get the following logged in debug;
socket.io:client client close with reason transport close +2s
socket.io:socket closing socket - reason transport close +1ms
socket.io:client ignoring remove for -0BK2XTmK98svWTNAAAA +1ms
****************** user disconnected ******************* -0BK2XTmK98svWTNAAAA
note the line socket.io:client ignoring remove for -0BK2XTmK98svWTNAAAA
but after that and with no other clients connected to the server I'm still seeing it trying to write data to a client that already left. (in the example below this is what I get after I've had 2 clients connected, both of which have since disconnected.
socket.io:client ignoring packet write {"type":2,"data":["k1",{"item":"switch2","datapoint":{"type":"SWITCH","state":"0"}}],"nsp":"/"} +1ms
socket.io:client ignoring packet write {"type":2,"data":["k1",{"item":"switch2","datapoint":{"type":"SWITCH","state":"0"}}],"nsp":"/"} +3ms
I'm trying to stop this apparently new behaviour so that once a client has disconnected and the server is idle its not still trying to send data out.
I've been playing about with socket.disconnect and delete socket["id"] but I'm still left with the same thing.
I tried with io.close() which sort of worked - it booted any clients who where actually connected and made them re-connect but still left the server sitting there trying to send updates to the client that had left.
Am I missing something obvious, or has there been a change in the way this is done with the new version of socket.io? There is nothing in the migration doc about this. The only other result I found was this bug report from June 2014 which has been marked as closed. From my reading of it - it appears to be the same problem I'm having but with the current version.
Update: I've done some more testing and added io.engine.clientsCount to both instances of console.log to track what it's doing. It appears when I connect 1 client it gives me 1 (as expected) and when I close that client it changes to 0 (as expected) this leads me to believe that the client connection has been closed and engine.io know this. So why am I still seeing all the 'ignoring packet write' lines and more with every client who has disconnected.
Update 2: I've updated the code above to include the parser section and the DB section - this represents the full node script as there was a thought that I may need to clean up my own clients. I have tried adding the following code to the script in the hope it would but alas not :(
In the connection event I added clients[socket.id] = socket; and the disconnection event I added delete clients[socket.id]; but it didn't change anything (that I could see)
Update 3: Answer thanks to #robertklep It was an 'event handler leak' that I was actually looking for. Having found that I also found this post.
My guess is that the newer socket.io is just showing you (by way of debug messages) a situation that was already happening in the old socket.io, where it just wasn't being logged.
I think the main issue is this setup:
var tail = cp.spawn('test-scripts/k1.rb');
io.on('connection', function(socket) {
...
tail.stdout.on('data', function(chunk) { ... });
...
});
This adds a new handler for each incoming connection. However, these won't miraculously disappear once the socket is disconnected, so they keep on trying to push new data through the socket (whether it's disconnected or not). It's basically an event handler leak, as they aren't getting cleaned up.
To clean up the handlers, you need to keep a reference to the handler function and remove it as a listener in the disconnect event handler:
var handler = function(chunk) { ... }:
tail.stdout.on('data', handler)
socket.on('disconnect', function() {
tail.stdout.removeListener('data', handler);
});
There's also a (slight) chance that you will get ignored packet writes from your MongoDB code, if the socket is closed before the forEach() has finished, but that may be acceptable (since the amount of data is finite).
PS: eventually, you should consider moving the processing code (what handler is doing) to outside the socket code, as it's now being run for each connected socket. You can create a separate event emitter instance that will emit the processed data, and subscribe to that from each new socket connection (and unsubscribe again when they disconnect), so they only have to pass the processed data to the clients.
This is most probably due to your connection is established via polling transport, which is sooo painful for developer. The reason is that this transport uses timeout to determine if the client is here or not.
The behavior you see is due to the client has left but next polling session opening moment has not come yet, and due to it server still thinks that client "it out there".
I have tried to "fight" this problem in many ways (like adding a custom onbeforeunload event on client side to force disconnect) but they all just do not work in 100% cases when polling is used as transport.
I need to send data to nodejs server via socket.io when the user closes the browser tab .
I tried doing :
var data={};
window.onbeforeunload = function() {
// i have a object to be sent
data.data1='abcd';
data.data2=1234;
socket.emit("senddata",data);
}
This code works when the user navigates around clicking links on the site but doesnot work when the user closes the browser tab
I also tried configuring the socket io on server side as below .. thinking the error may be due to socket connection being closed before emitting data:
var io = require('socket.io').listen(app.listen(port));
io.configure(function () {
io.set('close timeout',12000);
});
It also didnt work most of the time.
I also tried this on client side:
var socket = require('socket.io').listen(80, {
"sync disconnect on unload":false
});
It also did not work
I had tried receiving data like this
var io = require('socket.io').listen(app.listen(port));
io.sockets.on('connection', function (socket) {
socket.on('senddata', function (data) {
// data processing
});
});
please ..help me with this problem..thanks in advance..
When user connects - register on server side the time it happened.
Socket.IO has heart beating and pinging functionality. So just subscribe to disconnect event on server side and once it happens - means client disconnected - and you have on server time when client had connection. So that way you have timespan of client session.
Do not trust client to tell you any time or important data, as client can simply 'lie' - which leads to hacks/cheats/bugs on your server-side.
There is no reliable way to send data just before disconnect from client-side at all. There is nothing in Socket.IO for that, nor in just one of transports (WebSockets). As well as there is too many different scenarios of disconnection (power off, force close, ethernet cable out, wifi lose, etc).
I'm building a simple system like a realtime news feed, using node.js + socket.io.
Since this is a "read-only" system, clients connect and receive data, but clients never actually send any data of their own. The server generates the messages that needs to be sent to all clients, no client generates any messages; yet I do need to broadcast.
The documentation for socket.io's broadcast (end of page) says
To broadcast, simply add a broadcast flag to emit and send method calls. Broadcasting means sending a message to everyone else except for the socket that starts it.
So I currently capture the most recent client to connect, into a variable, then emit() to that socket and broadcast.emit() to that socket, such that this new client gets the new data and all the other clients. But it feels like the client's role here is nothing more than a workaround for what I thought socket.io already supported.
Is there a way to send data to all clients based on an event initiated by the server?
My current approach is roughly:
var socket;
io.sockets.on("connection", function (s) {
socket = s;
});
/* bunch of real logic, yadda yadda ... */
myServerSideNewsFeed.onNewEntry(function (msg) {
socket.emit("msg", { "msg" : msg });
socket.broadcast.emit("msg", { "msg" : msg });
});
Basically the events that cause data to require sending to the client are all server-side, not client-side.
Why not just do like below?
io.sockets.emit('hello',{msg:'abc'});
Since you are emitting events only server side, you should create a custom EventEmitter for your server.
var io = require('socket.io').listen(80);
events = require('events'),
serverEmitter = new events.EventEmitter();
io.sockets.on('connection', function (socket) {
// here you handle what happens on the 'newFeed' event
// which will be triggered by the server later on
serverEmitter.on('newFeed', function (data) {
// this message will be sent to all connected users
socket.emit(data);
});
});
// sometime in the future the server will emit one or more newFeed events
serverEmitter.emit('newFeed', data);
Note: newFeed is just an event example, you can have as many events as you like.
Important
The solution above is better also because in the future you might need to emit certain messages only to some clients, not all (thus need conditions). For something simpler (just emit a message to all clients no matter what), io.sockets.broadcast.emit() is a better fit indeed.
I am using node.js for long held connections. I want to know how I can detect when the client connection closes (maybe when the user closes the tab). How do I specify a callback for that?
Answering my own question - You can detect close of client connection by doing:
http.createServer(function(request, response) {
request.connection.addListener('close', function () {
// callback is fired when connection closed (e.g. closing the browser)
});
}
Take a look at Socket.io. It supports the following transports with fallbacks in this order:
WebSocket
Adobe Flash Socket
AJAX long polling
AJAX multipart streaming
Forever Iframe
JSONP Polling
The benefit is you'll be able to handle a lot more concurrent connections than long polling alone. In addition you'll get a rich set of features like heartbeats and disconnects.
io.sockets.on('connection', function (socket) {
// ... other socket handlers here ...
socket.on('disconnect', function () {
// do something to handle the disconnect
});
});