I have started to learn web sockets. It is must learn technology in today's time.
But i am curious to learn more about it. My basic question is How many WebSocket connection can be created on Client Side.
My Typically Application is html UI based and on the server i have rest based services. I need to track whether
Session timeout has happed or not
Whether Connection to the server is lost or not ? A kind of pooling program to check with connections is alive or not.
So I am creating 2 websocket objects on client and different url for them.
I hope i have implemented it correctly ?
Basically Browser closes the old websocket connection once you opened to new connection to SAME URL(ws://127.0.0.1:8080/WebSocket-context-root/getResource). You can keep small hack like "ws://127.0.0.1:8080/WebSocket-context-root/getResource/"+k. where k is any number/any random string. On server side just ignore the path variable k.
In this way you can open many number of connection at same time. Browser restriction of max-number-connection per domain is not applying here (Tested on Firefox). I tried max 25 parallel connections.
You can use websocket.readyState to check the status of the web socket connection.
onclose Event of the Web socket have reason code for closed connection.
User below code to test number of active connections.
var x=0
var intervalID = setInterval(function () {
websocket = new WebSocket("ws://127.0.0.1:8080/WebSocketApi/web/chat/"+x);
websocket.onopen = function (evt) {
console.log('open')
}
websocket.onmessage = function (evt) {
console.log('msg');
}
websocket.onclose= function (evt) {
console.log('closed');
}
if (++x === 15) {
window.clearInterval(intervalID);
}
}, 1);
Related
I'm new to node and to feathersjs, and for my first app, I'm trying to have different parts of it communicate using channels. I understand the operations and how they're used, but I don't understand how to establish a connection to a channel in the first place.
For example, here's some code from the official documentation:
app.on('login', (payload, { connection }) => {
if(connection && connection.user.isAdmin) {
// Join the admins channel
app.channel('admins').join(connection);
// Calling a second time will do nothing
app.channel('admins').join(connection);
}
});
Where does "connection" come from? There is no built-in function (unless I'm missing something obvious) in feathersjs to do this.
Thanks!
Channel is used in feathers to achieve real time.
In the server you need to configure socketio. Then it also requires the client to be connected to the server via socketio.
Where does "connection" come from?
connection is a js object that represents the connection the user has established by logging in.
Try doing a console.log(connection) to see what it contains.
connection is in this case passed by the Feathers framework in the function call to the function that you have quoted.
Once you have obtained this connection object then you can use it for adding the user to a channel, and many other things.
I'm writing a new SPA application that will subscribes to several rooms for several types of information updates.
In my production setup I'll use two servers behind a load balancer for reliability.
In the event of disconnect - Does the client have to resend the request for rooms subscriptions on the reconnect event callback, or is there a way to have the server reconnect the client automatically (even when the client reconnects to a different server due to server failure) ?
Socket.io will unsubscribe your users from all rooms on a disconnect. It will unsubscribe you from the server side. I played around with this a little. The server can store your user's rooms in redis or a database under the user ID and, upon connecting, check to see if that user should be in any of these rooms. At which time your user can join them from the server side without ever having to do anything from the client.
The problem is that this list of rooms must be constantly stored and updated. It's just another thing that has to work seamlessly on the backend. It's a lot of tests to consider all the possibilities that could mess up your organization. Like, what if they log in on another device, you have to clear the rooms and put in new ones, but if the user opens his laptop again and it reconnects, now he has to get back in those rooms from his laptop. ...It's totally doable/solvable, but I only did this on the front end:
// rejoin if there's a disconnect
mySocket.on('reconnect', () => {
mySocket.emit('subscribe', 'theRoom')
})
...and no further hassle. If you added some more details about why it's necessary to do it from the server..?
From my experience, I found this to be the easiest and useful solution:
Client side:
// the next 3 functions will be fired automatically on a disconnect.
// the disconnect (the first function) is not required, but you know,
// you can use it make some other good stuff.
socket.on("disconnect", function() {
console.log("Disconnected");
});
socket.on("reconnect", function() {
// do not rejoin from here, since the socket.id token and/or rooms are still
// not available.
console.log("Reconnecting");
});
socket.on("connect", function() {
// thats the key line, now register to the room you want.
// info about the required rooms (if its not as simple as my
// example) could easily be reached via a DB connection. It worth it.
socket.emit("registerToRoom", $scope.user.phone);
});
Server side:
io.on('connection', function(socket){
socket.on("registerToRoom", function(userPhone) {
socket.join(userPhone);
});
});
And thats it. Very simple and straight forward.
You also can add in the connected socket (the last function) some more updates to the user display, such as refreshing its index or something else.
Socket.io does have a reconnect event - Docs here
Something like the below should work
socket.on('reconnect', () => attemptReconnection())
The attempt reconnection callback would look something like:
const attemptReconnection = () => socket.emit('joinRoom', roomId)
I have to implement a chat application using websocket, users will chat via groups, there can be thousands of groups and a user can be in multiple groups. I'm thinking about 2 solutions:
[1] for each group chat, I create a websocket endpoint (using camel-atmosphere-websocket), users in the same group can subscribe to the group endpoint and send/receive message over that endpoint. it means there can be thousands of websocket endpoints. Client side (let's say iPhone) has to subscribes to multiple wbesocket endpoints. is this a good practice?
[2] I just create one websocket endpoint for all groups. Client side just subscribes to this endpoint and I manage the messages distribution myself on server: get group members, pick the websocket of each member from list of connected websockets then write the message to each member via websocket.
Which solution is better in term of performance and easy to implement on both client and server?
Thanks.
EDIT 2015-10-06
I chose the second approach and did a test with jetty websocket client, I use camel atmosphere websocket on server side. On client side, I create websocket connections to server in threads. There was a problem with jetty that I can just create around 160 websocket connections (it means around 160 threads). The result is that I almost see no difference when the number of clients increases from 1 to 160.
Yes, 160 is not a big number, but I think I will do more test when I actually see the performance problem, for now, I'm ok with second approach.
If you are interested in the test code, here it is:
http://www.eclipse.org/jetty/documentation/current/jetty-websocket-client-api.html#d0e22545
I think second approach will be better to use for performance. I am using the same for my application, but it is still in testing phase so can't comment about the real time performance. Now its running for 10-15 groups and working fine. In my app, there is similar condition like you in which user can chat based on group. I am handling the the group creation on server side using node.js. Here is the code to create group, but it is for my app specific condition. Just pasting here for the reference. Getting homeState and userId from front-end. Creating group based on the homeState. This code is only for example, it won't work for you. To improve performance you can use clustering.
this.ConnectionObject = function(homeState, userId, ws) {
this.homeState = homeState;
this.userId = userId;
this.wsConnection = ws;
},
this.createConnectionEntry = function(homeState, userId,
ws) {
var connObject = new ws.thisRefer.ConnectionObject(homeState, userId,
ws);
var connectionEntryList = null;
if (ws.thisRefer.connectionMap[homeState] != undefined) {
connectionEntryList = ws.thisRefer.connectionMap[homeState];
} else {
connectionEntryList = new Array();
}
connectionEntryList.push(connObject);
console.log(connectionEntryList.length);
ws.thisRefer.connectionMap[homeState] = connectionEntryList;
ws.thisRefer.connecteduserIdMap[userId] = "";
}
Browsers implement a restriction on the numbers of websocket that can be opened by the same tab. You can't rely on being able to create as many connection as possible. Go for solution #2
My website has an IM with several users connected. From my client I wish to disconnect a particular user. Here is the code I am trying:
// client side
function deleteUser(delCallsign)
{
delCallsign = delCallsign.toUpperCase();
socket.emit('deleteuser', delCallsign); // send it to the server for delete
}
// server side
socket.on('deleteuser', function(callsign)
{
socket.disconnect(usernames[callsign]);
io.sockets.emit('updateusers', usernames);
});
Using an alert, I have verified that I'm calling the server side function with the username I wish to disconnect. But what happens is that I get disconnected, not the user specified. What am I doing wrong here?
On user connection you should record its socket.id which you would then call for deletion
io.sockets.on('connection',function(socket){
// Asign socket.id to variable
// socket.id;
});
socket.on('deleteuser', function(callsign) {
io.sockets.connected[usernames[callsign].id].disconnect();
io.sockets.emit('updateusers', usernames);
});
This is roughly the idea.
Based on those post:
SocketIO: disconnect client by socket id?
Get the client id of the message sender in socket.io?
-- More Relevent --
A little bit old but the same principals applies
how do I store socket resources from specific users with socket.io?
I have the following situation, where the already sent headers problem happens, when sending multiple request from the server to the client via AJAX:
It is something I expected since I opted to go with AJAX, instead of sockets. Is there is other way around to exchange the data between the server and the client, like using browserify to translate an emitter script for the client? I suppose that I can't escape the sockets, so I will take advice about simpler library, as sockets.io seems too complex for such a small operation.
//-------------------------
Update:
Here is the node.js code as requested.
var maxRunning = 1;
var test_de_rf = ['rennen','ausgehen'];
function callHandler(word, cb) {
console.log("word is - " + word);
gender.gender_function_rf( word , function (result_rf) {
console.log(result_rf);
res.send(result_rf);// Here I send data back to the ajax call
setTimeout(function() { cb(null);
}, 3000);
});
}
async.eachLimit(test_de_rf, maxRunning, function(item, done) {
callHandler(item, function(err) {
if (err) throw new Error(err);
done();
});
}, function(err) {
if (err) throw new Error(err);
console.log('done');
});
res.send() sends and finishes an http response. You can only call it once per request because the request is finished and done after calling that. It is a fairly high level way of sending a response (does it all at once in one call).
If you wanted to have several different functions contributing to a response, you could use the lower level functions on the http object such as res.setHeader(), res.writeHead(), res.write() (which you can call multiple times) and res.end() (which indicates the end of the response).
You can use the standard webSocket API in the browser and get webSocket module for server-side support or you can use socket.io which offers both client and server support and a number of higher level functions (such as automatic reconnect, automatic failover to http polling if webSockets are not supported, etc...).
All that said, if what you really want is the ability to just send some data from server to client whenever you want, then a webSocket is really the better way to go. This is a persistent connection, is supported by all modern browsers and allows the server to send data unsolicited to the client at any time. I'd hardly say socket.io is complex. The doc isn't particularly great at explaining things (not uncommon in the open source world as the node.js doc isn't particularly great either). But, I've always been able to figure advanced things out by just looking at a few runtime data structures in the debugger and/or looking at the source code.