We Keep Coding

How can I check whether an application is installed from a web browser?

This is for Windows.
I have a flash application I am converting to AIR. I built a captive installer using NSIS and it works fine. However I would like to have an icon on a website which checks if the application is already installed and ask the user if they wish to run it. If it is not installed, they get the option to download it.
I am fairly certain this is doable, because Zoom and GoToMeeting both do this.
My searching skills seem to be failing me when looking for this.
Edit:
It appears the best/only way to do this is to create a custom protocol for the application. Something like DoDaApp://.
Which brings up the next set of questions;
How to create an NSIS file which will create the appropriate registry entries on the client computer? As a user, not admin.
How to check if the protocol is currently installed on the computer?

This is a partial answer as it does not work in Edge. I'll explain the issue below.
As recommended in How to detect browser's protocol handlers you can use timeout & blur event handlers. Here is my interpretation of the code;
function checkCustomProtocol(inProtocol,inInstalLink,inTimeOut)
{
var timeout = inTimeOut;
window.addEventListener('blur',function(e)
{
window.clearTimeout(timeout);
}
)
timeout = window.setTimeout(function()
{
console.log('timeout');
window.location = inInstalLink;
}, inTimeOut
);
window.location = inProtocol;
}
Microsoft Edge is ever so helpful by popping up a dialog box telling you "You'll Need a new app to open this" which "blurs" the screen, not allowing download of the file.
So I will be posting another question on how to make it work in Edge. I have reviewed ismailhabib's code but the known issues section says it doesn't work with Edge either.

Here is a more complete answer. It has been lightly tested in IE 11, Microsoft Edge, Chrome and Firefox. I also added comments;
/*
checkCustomProtocol - check if custom protocol exists
inProtocol - URL of application to run eg: MyApp://
inInstallLink - URL to run when the protocol does not exist.
inTimeOut - time in miliseconds to wait for application to Launch.
*/
function checkCustomProtocol(inProtocol,inInstalLink,inTimeOut)
{
// Check if Microsoft Edge
if (navigator.msLaunchUri)
{
navigator.msLaunchUri(inProtocol, function ()
{
//It launched, nothing to do
},
function()
{
window.location = inInstalLink; //Launch alternative, typically app download.
}
);
}
else
{
// Not Edge
var timeout = inTimeOut;
//Set up a listener to see if it navigates away from the page.
// If so we assume the papplication launched
window.addEventListener('blur',function(e)
{
window.clearTimeout(timeout);
}
)
//Set a timeout so that if the application does not launch within the timeout we
// assume the protocol does not exist
timeout = window.setTimeout(function()
{
console.log('timeout');
window.location = inInstalLink; //Try to launch application
}, inTimeOut
);
window.location = inProtocol; //Launch alternative, typically app download.
}
}

WebRTC video streaming in PubNub

I've recently gotten my hands on the WebRTC sdk by PubNub. Everything's been going great but I've been having trouble displaying video from a client to my screen.
As mentioned in their documentations and tutorial I've written the following code:
function login(form) {
var pub = <publish_key>;
var sub = <subscribe_key>;
var phone = window.phone = PHONE({
number : form.username.value,
publish_key : pub,
origin :'pubsub.pubnub.com',
subscribe_key : sub,
//media : { audio : true, video : true }
ssl :true
});
var ctrl = window.ctrl = CONTROLLER(phone);
ctrl.ready(function(){
form.username.style.background="#55ff5b";
form.login_submit.hidden="true"; // Hide login button
ctrl.addLocalStream(vid_thumb);
});
ctrl.receive(function(session){
session.connected(function(session){
video_out.appendChild(session.video);
});
session.ended(function(session) { ctrl.getVideoElement(session.number).remove(); });
});
}
function makeCall(){
if (!window.phone) alert("Login First!");
var num = form.number.value;
if (phone.number()==num) return false; // No calling yourself!
ctrl.dial(num);
return false;
}
Evrything seems to be working, but the actual video is not being shown on my screen.
(I'm using chrome browsers on both machines)
Can anybody please help out?
Thanks

i got the solution..
Its a very weird solution though and i cant really say how it solved my problem..
I was previously putting my javascript codes in another script file and then linking that file to my HTML page. But as soon i transferred those code to my HTML page everything seemed to work just fine.
Thanks everyone.

WebRTC Video Streaming in PubNub P2P
Answer: WebRTC running on localhost with HTTPS
We answered a similar question yesterday. You can find the answer here in the following Stackoverflow answer link. Essentially you need to make sure you are running HTTPS locally and also using the correct variable scoping as mentioned by Craig Conover.
And you can find the source code on github gist.

What is the best technology for a chat/shoutbox system? Plain JS, JQuery, Websockets, or other?

I have an old site running, which also has a chat system, which always used to work fine. But recently I picked up the project again and started improving and the user base has been increasing a lot. (running on a VPS)
Now this shoutbox I have (running at http://businessgame.be/shoutbox) has been getting issues lately, when there are over 30 people online at the same time, it starts to really slow down the entire site.
This shoutbox system was written years ago by the old me (which ironically was the young me) who was way too much into old school Plain Old JavaScript (POJS?) and refused to use frameworks like JQuery.
What I do is I poll every 3 seconds with AJAX if there are new messages, and if YES, load all those messages (which are handed as an XML file which is then parsed by the JS code into HTML blocks which are added to the shoutbox content.
Simplified the script is like this:
The AJAX functions
function createRequestObject() {
var xmlhttp;
if (window.XMLHttpRequest) { // code for IE7+, Firefox, Chrome, Opera, Safari
xmlhttp = new XMLHttpRequest();
} else { // code for IE6, IE5
xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
}
// Create the object
return xmlhttp;
}
function getXMLObject(XMLUrl, onComplete, onFail) {
var XMLhttp = createRequestObject();
// Check to see if the latest shout time has been initialized
if(typeof getXMLObject.counter == "undefined") {
getXMLObject.counter = 0;
}
getXMLObject.counter++;
XMLhttp.onreadystatechange = function() {
if(XMLhttp.readyState == 4) {
if(XMLhttp.status == 200) {
if(onComplete) {
onComplete(XMLhttp.responseXML);
}
} else {
if(onFail) {
onFail();
}
}
}
};
XMLhttp.open("GET", XMLUrl, true);
XMLhttp.send();
setTimeout(function() {
if(typeof XMLhttp != "undefined" && XMLhttp.readyState != 4) {
XMLhttp.abort();
if(onFail) {
onFail();
}
}
}, 5000);
}
Chat functions
function initShoutBox() {
// Check for new shouts every 2 seconds
shoutBoxInterval = setInterval("shoutBoxUpdate()", 3000);
}
function shoutBoxUpdate() {
// Get the XML document
getXMLObject("/ajax/shoutbox/shoutbox.xml?time=" + shoutBoxAppend.lastShoutTime, shoutBoxAppend);
}
function shoutBoxAppend(xmlData) {
process all the XML and add it to the content, also remember the timestamp of the newest shout
}
The real script is far more convoluted, with slower loading times when the page is blurred and keeping track of AJAX calls to avoid double calls at the same time, ability to post a shout, load settings etc. All not very relevant here.
For those interested, full codes here:
http://businessgame.be/javascripts/xml.js
http://businessgame.be/javascripts/shout.js
Example of the XML file containing the shout data
http://businessgame.be/ajax/shoutbox/shoutbox.xml?time=0
I do the same for getting a list of the online users every 30 seconds and checking for new private messages every 2 minutes.
My main question is, since this old school JS is slowing down my site, will changing the code to JQuery increase the performance and fix this issue? Or should I choose to go for an other technology alltogether like nodeJS, websockets or something else? Or maybe I am overlooking a fundamental bug in this old code?
Rewriting an entire chat and private messages system (which use the same backend) requires a lot of effort so I'd like to do this right from the start, not rewriting the whole thing in JQuery, just to figure out it doesn't solve the issue at hand.
Having 30 people online in the chatbox at the same time is not really an exception anymore so it should be a rigid system.
Could perhaps changing from XML data files to JSON increase performance as well?
PS: Backend is PHP MySQL

I'm biased, as I love Ruby and I prefer using Plain JS over JQuery and other frameworks.
I believe you're wasting a lot of resources by using AJAX and should move to websockets for your use-case.
30 users is not much... When using websockets, I would assume a single server process should be able to serve thousands of simultaneous updates per second.
The main reason for this is that websockets are persistent (no authentication happening with every request) and broadcasting to a multitude of connections will use the same amount of database queries as a single AJAX update.
In your case, instead of everyone reading the whole XML every time, a POST event will only broadcast the latest (posted) shout (not the whole XML), and store it in the XML for persistent storage (used for new visitors).
Also, you don't need all the authentication and requests that end up being answered with a "No, there aren't any pending updates".
Minimizing the database requests (XML reads) should prove to be a huge benefit when moving from AJAX to websockets.
Another benifit relates to the fact that enough simultaneous users will make AJAX polling behave the same as a DoS attack.
Right now, 30 users == 10 requests per second. This isn't much, but it can be heavy if each request would take more than 100ms - meaning, that the server answers less requests than it receives.
The home page for the Plezi Ruby Websocket Framework has this short example for a shout box (I'm Plezi's author, I'm biased):
# finish with `exit` if running within `irb`
require 'plezi'
class ChatServer
def index
render :client
end
def on_open
return close unless params[:id] # authentication demo
broadcast :print,
"#{params[:id]} joind the chat."
print "Welcome, #{params[:id]}!"
end
def on_close
broadcast :print,
"#{params[:id]} left the chat."
end
def on_message data
self.class.broadcast :print,
"#{params[:id]}: #{data}"
end
protected
def print data
write ::ERB::Util.html_escape(data)
end
end
path_to_client = File.expand_path( File.dirname(__FILE__) )
host templates: path_to_client
route '/', ChatServer
The POJS client looks like so (the DOM update and from data access ($('#text')[0].value) use JQuery):
ws = NaN
handle = ''
function onsubmit(e) {
e.preventDefault();
if($('#text')[0].value == '') {return false}
if(ws && ws.readyState == 1) {
ws.send($('#text')[0].value);
$('#text')[0].value = '';
} else {
handle = $('#text')[0].value
var url = (window.location.protocol.match(/https/) ? 'wss' : 'ws') +
'://' + window.document.location.host +
'/' + $('#text')[0].value
ws = new WebSocket(url)
ws.onopen = function(e) {
output("<b>Connected :-)</b>");
$('#text')[0].value = '';
$('#text')[0].placeholder = 'your message';
}
ws.onclose = function(e) {
output("<b>Disonnected :-/</b>")
$('#text')[0].value = '';
$('#text')[0].placeholder = 'nickname';
$('#text')[0].value = handle
}
ws.onmessage = function(e) {
output(e.data);
}
}
return false;
}
function output(data) {
$('#output').append("<li>" + data + "</li>")
$('#output').animate({ scrollTop:
$('#output')[0].scrollHeight }, "slow");
}
If you want to add more events or data, you can consider using Plezi's auto-dispatch feature, that also provides you with an easy to use lightweight Javascript client with an AJAJ (AJAX + JSON) fallback.
...
But, depending on your server's architecture and whether you mind using heavier frameworks or not, you can use the more common socket.io (although it starts with AJAX and only moves to websockets after a warmup period).
EDIT
Changing from XML to JSON will still require parsing. The question is actually whether XML vs. JSON parsing speeds.
JSON will be faster on the client javascript, according to the following SO question and answer: Is parsing JSON faster than parsing XML
JSON seems to be also favored on the server-side for PHP (might be opinion based rather than tested): PHP: is JSON or XML parser faster?
BUT... I really think your bottleneck isn't the JSON or the XML. I believe the bottleneck relates to the multitude of times that the data is accessed, (parsed?) and reviewed by the server when using AJAX.
EDIT2 (due to comment about PHP vs. node.js)
You can add a PHP websocket layer using Ratchet... Although PHP wasn't designed for long running processes, so I would consider adding a websocket dedicated stack (using a local proxy to route websocket connections to a different application).
I love Ruby since it allows you to quickly and easily code a solution. Node.js is also commonly used as a dedicated websocket stack.
I would personally avoid socket.io, because it abstracts the connection method (AJAX vs Websockets) and always starts as AJAX before "warming up" to an "upgrade" (websockets)... Also, socket.io uses long-polling when not using websockets, which I this is terrible. I'd rather show a message telling the client to upgrade their browser.
Jonny Whatshisface pointed out that using a node.js solution he reached a limit of ~50K concurrent users (which could be related to the local proxy's connection limit). Using a C solution, he states to have no issues with more than 200K concurrent users.
This obviously depends also on the number of updates per second and on whether you're broadcasting the data or sending it to specific clients... If you're sending 2 updates per user per second for 200K users, that's 400K updates. However, updating all the users only once every 2 seconds, that's 100K updates per second. So trying to figure out the maximum load can be a headache.
Personally, I didn't get to reach these numbers on my apps, so I never got to discover Plezi's limits first hand... although, during testing, I had no issues with sending hundred of thousands of updates per second (but I did had a connection limit due to available ports and open file handle limits on my local machine).
This definitely shows how vast of an improvement you can reach by utilizing websockets (especially since you stated to notice slowdowns with 30 concurrent users).

Can I use gamepads with Node-Webkit (NW.js)?

I am building a NW.js (Node-Webkit) dashboard app which I want to be able to control with a game controller (for example: XBox 360 controller or Logitech controller).
I'm calling the following onready but when I debug its not recognizing any gamepads.
angular.element(document).ready(function() {
if(canGame()) {
var prompt = "To begin using your gamepad, connect it and press any button!";
$("#gamepadPrompt").text(prompt);
$(window).on("gamepadconnected", function() {
$("#gamepadPrompt").html("Gamepad connected!");
console.log("connection event");
});
$(window).on("gamepaddisconnected", function() {
console.log("disconnection event");
$("#gamepadPrompt").text(prompt);
});
}
});
function canGame() {
return "getGamepads" in navigator;
}
When I debug the code, it doesn't appear to be detecting any gamepads. I also try:
navigator.webkitGetGamepads()
but it doesn't show any gamepads being detected either.
Has anyone successfully used gamepads with a NW.js app?
I would greatly appreciate some help getting this to work.

I found the answer to my issue. Gamepads are indeed compatible with NW.js. I however, was using an old version (~v0.08).
The code I posted earlier when running with NW.js v0.12.2.

Node.js / Server.js socket implementation problems

Having a hard time implementing a node.js/server.js setup
I'm a bit stuck right now, and hoping someone can shed some light. I'm relatively new to sockets in general, but have been programming in javascript on and off for several years, although only about as deep as is necessary to accomplish the task at hand. As a result, my understanding of some of the concepts surrounding the javascript stack heap, and sockets in general are somewhat limited.
Ok Here's the situation:
I've created an application intended to simply increment a counter, on several machines. Several users can click the "next" button and it will update instantly on all machines.
When you first connect, it retrieves the current number, and spits it out locally.
I've created the server here:
var io = require("socket.io");
var sockets = io.listen(8000);
var currentlyServing=0;
sockets.on("connection", function (socket)
{
console.log("client connected");
socket.emit("receive", currentlyServing);
socket.on("update", function(serving)
{
currentlyServing=serving;
if(currentlyServing>100)
currentlyServing=0;
if(currentlyServing<0)
currentlyServing=99;
socket.broadcast.emit("receive", currentlyServing);
console.log("update received: "+currentlyServing);
});
});
console.log("Server Started");
Here is the relevant (I hope) excerpt from the client side:
var socket = io.connect("http://www.sampledomain.com:8000");
//function to update the page when a new update is received
socket.on("receive", function(receivedServing)
{
document.getElementById('msgs').value=""+String("00" + receivedServing).slice(-2);
document.getElementById('nowServing').value=receivedServing;
});
//this is called in an onClick event in the HTML source
//sends the new number to all other stations except this one (handled by server side)
function nextServing()
{
var sendServing = parseInt(document.getElementById('nowServing').value)+1;
socket.emit("update", sendServing);
document.getElementById('nowServing').value=sendServing;
document.getElementById('msgs').value=""+String("00" + sendServing).slice(-2);
}
Ok so here's my problem. This runs absolutely fine in every system I've put it in, smoothly and beautifully - except for IE8. If left alone for more than 2-3 minutes (with no activity at all), I eventually receive a "stack overflow" error. The line number it appears on fluctuates (haven't determined the factors involved yet), but it always happens at that interval. On some workstations it takes longer, which I'm beginning to think has a direct correlation to the amount of phsyical RAM the machine has, or at least how much is being allocated to the web browser.
I found an online function to determine "max stack size", which I realize is not an exact science, however I did consistently get a number in the area of 3000. On my IE11 machine with considerable more resources, I found it to be in the area of 20,000. This may not be relevant, but I figured the more info the better :)
To avoid this problem for now so that the end users don't see this error message, I've take the entire client script, and put it into an iFrame which reloads itself every 60 seconds,essentially resetting the stack, which feels so dirty sitting so close to a web socket, but has bought me the time to post here. I've googled until I can't google any more, but when you search "node.js" or "socket.io" along with "stack overflow" on google, you just get a lot of posts about the two topics that are hosted on the stackoverflow dot com website. ARG lol
Anyone?
EDIT ON NOVEMBER 18TH 2014 AS PER COMMENTS BELOW:
the error message is most often claiming stack overflow at line 1056. IE Developer tools points towards the file socket.io.js. Line 1056 is:
return fn.apply(obj, args.concat(slice.call(arguments)));
which is insdie this section of the file:
var slice = [].slice;
/**
* Bind `obj` to `fn`.
*
* #param {Object} obj
* #param {Function|String} fn or string
* #return {Function}
* #api public
*/
module.exports = function(obj, fn){
if ('string' == typeof fn) fn = obj[fn];
if ('function' != typeof fn) throw new Error('bind() requires a function');
var args = slice.call(arguments, 2);
return function(){
return fn.apply(obj, args.concat(slice.call(arguments)));
}
};

From what I've read it seems that the problem on IE8 might be related to flash. It IE8 uses flashsocket as the default configuration. I suggest to try the following on the client side:
if(navigator.appName.indexOf("Internet Explorer")!=-1 && navigator.appVersion.indexOf("MSIE 8")==-1 ){
socket = io.connect("http://www.sampledomain.com:8000", {
transports: ['xhr-polling']
});
}
else
{
socket = io.connect("http://www.sampledomain.com:8000" );
}
This should make IE8 use long polling while all other machines use the best method they can.
On a side note: You might also want to consider incrementing the "serving" variable on the server.

Find existing issue Causes a "Stack Overflow" in IE8 when using xhr-polling #385.
This was fixed by disabling Flash.
Also find Safari over windows client use xhr-polling instead of websocket - performance are severely harm #1147. While this is Safari it may apply to IE8 because it is using similar mechanism.
I did a small test using your socket.io but in IE 10 and emulated IE8
so that I could debug well. Started capturing Network in the tab and
noticed the requests logging every few seconds.Left alone for few
minutes and I see a lot of requests logged in. You will not see this
in Chrome because it has true WebSockets. While IE8 does not support
WebSockets socket.io emulate that using plain HTTP GET/POST using some
mechanism. So my theory is that even if socket.io works with IE8 it
does not reliably emulate web sockets
My advice is to rule out IE 8 for long running client application. IE8 is no longer supported by Microsoft.

maybe try to replace
""+String("00" + receivedServing).slice(-2)
with
('00' + receivedServing).slice(-2)