Related
I am using Piwik/Matomo's tracker to provide my users with custom JS trackers, and provide a curated dashboard of analytics that are tailor made for them. One problem I am facing consistently is verifying if the tracker is installed and working correctly.
I have tried using file_get_contents and/or cURL to fetch the page and check if the tracker exists, but this doesn't always work. So I am trying to instead simulate a visit, and see if the tracker sends me any data when it happens.
Since fget/curl do not trigger javascript, is there an alternative (and lightweight) method to fire the page's javascript and trigger a visit for testing?
Update : I implemented this by using PhantomJS as suggested, with the overall function being something like this. Haven't yet tested this extensively for all my users, is there a more elegant solution? -
checktracker
{
if (data exists & data > 0)
{
return true
}
else if (data exists & data = 0)
{
simulate visit with phantomJS //Relevant to question
check again
if ( still 0 )
{
return false
}
else
{
return true
}
}
else
{
invalid site id
}
}
So you want to automatically check if a specific website has integrated Matomo correctly? I recently wanted to do the same to create a browser extention to quickly debug common errors.
One way would be checking the DOM. The Matomo Tracking Code adds a <script>-Tag to the website, so you can check the existence of it via JavaScript:
function getDomElements() {
var allElements = document.getElementsByTagName('script');
for (var i = 0, n = allElements.length; i < n; i++) {
if (allElements[i].hasAttribute("src") && allElements[i].getAttribute("src").endsWith("piwik.js")) { // TODO: support renamed piwik.js
return allElements[i];
}
}
}
But if you also have access to the JS console, the probably better solution would be checking if the tracking code has initialized correctly:
If something like this outputs your Matomo URL, chances are high that the tracking code is embedded correctly.
var tracker == window.Piwik.getAsyncTracker()
console.log(tracker.getPiwikUrl())
Of course it can still fail (e.g. if the server returns 403 on the piwik.php request, but if you control the server, this shouldn't happen)
To run the check automatically, you could look into Headless Chrome or Firefox.
So I have a system that essentially enabled communication between two computers, and uses a WebRTC framework to achieve this:
"The Host": This is the control computer, and clients connect to this. They control the clients window.
"The Client": The is the user on the other end. They are having their window controlled by the server.
What I mean by control, is that the host can:
change CSS on the clients open window.
control the URL of an iframe on the clients open window
There are variations on these but essentially thats the amount of control there is.
When "the client" logs in, the host sends a web address to the client. This web address will then be displayed in an iframe, as such:
$('#iframe_id').attr("src", URL);
there is also the ability to send a new web address to the client, in the form of a message. The same code is used above in order to navigate to that URL.
The problem I am having is that on, roughly 1 in 4 computers the iframe doesn't actually load. It either displays a white screen, or it shows the little "page could not be displayed" icon:
I have been unable to reliably duplicate this bug
I have not seen a clear pattern between computers that can and cannot view the iframe content.
All clients are running google chrome, most on an apple powermac. The only semi-link I have made is that windows computers seem slightly more susceptible to it, but not in a way I can reproduce. Sometimes refreshing the page works...
Are there any known bugs that could possibly cause this to happen? I have read about iframe white flashes but I am confident it isn't that issue. I am confident it isn't a problem with jQuery loading because that produces issues before this and would be easy to spot.
Thanks so much.
Alex
edit: Ok so here is the code that is collecting data from the server. Upon inspection the data being received is correct.
conn.on('data', function(data) {
var data_array = JSON.parse(data);
console.log(data_array);
// initialisation
if(data_array.type=='init' && inititated === false) {
if(data_array.duration > 0) {
set_timeleft(data_array.duration); // how long is the exam? (minutes)
} else {
$('#connection_remainingtime').html('No limits');
}
$('#content_frame').attr("src", data_array.uri); // url to navigate to
//timestarted = data_array.start.replace(/ /g,''); // start time
ob = data_array.ob; // is it open book? Doesnt do anything really... why use it if it isnt open book?
snd = data_array.snd; // is sound allowed?
inititated = true;
}
}
It is definitele trying to make the iframe navigate somewhere as when the client launches the iframe changes - its trying to load something but failing.
EDIT: Update on this issue: It does actually work, just not with google forms. And again it isn't everybody's computers, it is only a few people. If they navigate elsewhere (http://www.bit-tech.net for example) then it works just fine.
** FURTHER UPDATE **: It seems on the ones that fail, there is an 'X-Frames-Origin' issue, in that its set the 'SAMEORIGIN'. I dont understand why some students would get this problem and some wouldn't... surely it depends upon the page you are navigating to, and if one person can get it all should be able to?
So the problem here was that the students were trying to load this behind a proxy server which has an issue with cookies. Although the site does not use cookies, the proxy does, and when the student had blocked "third party cookies" in their settings then the proxy was not allowing the site to load.
Simply allowed cookies and it worked :)
iframes are one of the last things to load in the DOM, so wrap your iframe dependent code in this:
document.getElementById('content_frame').onload = function() {...}
If that doesn't work then it's the document within the iframe. If you own the page inside the iframe then you have options. If not...setTimeout? Or window.onload...?
SNIPPET
conn.on('data', function(data) {
var data_array = JSON.parse(data);
console.log(data_array);
// initialisation
if (data_array.type == 'init' && inititated === false) {
if (data_array.duration > 0) {
set_timeleft(data_array.duration); // how long is the exam? (minutes)
} else {
$('#connection_remainingtime').html('No limits');
}
document.getElementById('content_frame').onload = function() {
$('#content_frame').attr("src", data_array.uri); // url to navigate to
//timestarted = data_array.start.replace(/ /g,''); // start time
ob = data_array.ob; // is it open book? Doesnt do anything really... why use it if it isnt open book?
snd = data_array.snd; // is sound allowed?
inititated = true;
}
}
}
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).
I have created a custom URL protocol handler.
http://
mailto://
custom://
I have registered a WinForms application to respond accordingly. This all works great.
But I would like to be able to gracefully handle the case where the user doesn't have the custom URL protocol handler installed, yet.
In order to be able to do this I need to be able to detect the browser's registered protocol handlers, I would assume from JavaScript. But I have been unable to find a way to poll for the information. I am hoping to find a solution to this problem.
Thanks for any ideas you might be able to share.
This would be a very, very hacky way to do this... but would this work?
Put the link in as normal...
But attach an onclick handler to it, that sets a timer and adds an onblur handler for the window
(in theory) if the browser handles the link (application X) will load stealing the focus from the window...
If the onblur event fires, clear the timer...
Otherwise in 3-5seconds let your timeout fire... and notify the user "Hmm, looks like you don't have the Mega Uber Cool Application installed... would you like to install it now? (Ok) (Cancel)"
Far from bulletproof... but it might help?
There's no great cross-browser way to do this. In IE10+ on Win8+, a new msLaunchUri api enables you to launch a protocol, like so:
navigator.msLaunchUri('skype:123456',
function()
{
alert('success');
},
function()
{
alert('failed');
}
);
If the protocol is not installed, the failure callback will fire. Otherwise, the protocol will launch and the success callback will fire.
I discuss this topic a bit further here:
https://web.archive.org/web/20180308105244/https://blogs.msdn.microsoft.com/ieinternals/2011/07/13/understanding-protocols/
This topic is of recent (2021) interest; see https://github.com/fingerprintjs/external-protocol-flooding for discussion.
HTML5 defines Custom scheme and content handlers (to my knowledge Firefox is the only implementor so far), but unfortunately there is currently no way to check if a handler already exists—it has been proposed, but there was no follow-up. This seems like a critical feature to use custom handlers effectively and we as developers should bring attention to this issue in order to get it implemented.
There seems to be no straightforward way via javascript to detect the presence of an installed app that has registered a protocol handler.
In the iTunes model, Apple provides urls to their servers, which then provide pages that run some javascript:
http://ax.itunes.apple.com/detection/itmsCheck.js
So the iTunes installer apparently deploys plugins for the major browsers, whose presence can then be detected.
If your plugin is installed, then you can be reasonably sure that redirecting to your app-specific url will succeed.
What seams the most easy solution is to ask the user the first time.
Using a Javascript confirm dialog per example:
You need this software to be able to read this link. Did you install it ?
if yes: create a cookie to not ask next time; return false and the link applies
if false: window.location.href = '/downloadpage/'
If you have control of the program you're trying to run (the code), one way to see if the user was successful in running the application would be to:
Before trying to open the custom protocol, make an AJAX request to a server script that saves the user's intent in a database (for example, save the userid and what he wanted to do).
Try to open the program, and pass on the intent data.
Have the program make a request to the server to remove the database entry (using the intent data to find the correct row).
Make the javascript poll the server for a while to see if the database entry is gone. If the entry is gone, you'll know the user was successful in opening the application, otherwise the entry will remain (you can remove it later with cronjob).
I have not tried this method, just thought it.
I was able to finally get a cross-browser (Chrome 32, Firefox 27, IE 11, Safari 6) solution working with a combination of this and a super-simple Safari extension. Much of this solution has been mentioned in one way or another in this and this other question.
Here's the script:
function launchCustomProtocol(elem, url, callback) {
var iframe, myWindow, success = false;
if (Browser.name === "Internet Explorer") {
myWindow = window.open('', '', 'width=0,height=0');
myWindow.document.write("<iframe src='" + url + "'></iframe>");
setTimeout(function () {
try {
myWindow.location.href;
success = true;
} catch (ex) {
console.log(ex);
}
if (success) {
myWindow.setTimeout('window.close()', 100);
} else {
myWindow.close();
}
callback(success);
}, 100);
} else if (Browser.name === "Firefox") {
try {
iframe = $("<iframe />");
iframe.css({"display": "none"});
iframe.appendTo("body");
iframe[0].contentWindow.location.href = url;
success = true;
} catch (ex) {
success = false;
}
iframe.remove();
callback(success);
} else if (Browser.name === "Chrome") {
elem.css({"outline": 0});
elem.attr("tabindex", "1");
elem.focus();
elem.blur(function () {
success = true;
callback(true); // true
});
location.href = url;
setTimeout(function () {
elem.off('blur');
elem.removeAttr("tabindex");
if (!success) {
callback(false); // false
}
}, 1000);
} else if (Browser.name === "Safari") {
if (myappinstalledflag) {
location.href = url;
success = true;
} else {
success = false;
}
callback(success);
}
}
The Safari extension was easy to implement. It consisted of a single line of injection script:
myinject.js:
window.postMessage("myappinstalled", window.location.origin);
Then in the web page JavaScript, you need to first register the message event and set a flag if the message is received:
window.addEventListener('message', function (msg) {
if (msg.data === "myappinstalled") {
myappinstalledflag = true;
}
}, false);
This assumes the application which is associated with the custom protocol will manage the installation of the Safari extension.
In all cases, if the callback returns false, you know to inform the user that the application (i.e., it's custom protocol) is not installed.
You say you need to detect the browser's protocol handlers - do you really?
What if you did something like what happens when you download a file from sourceforge? Let's say you want to open myapp://something. Instead of simply creating a link to it, create a link to another HTML page accessed via HTTP. Then, on that page, say that you're attempting to open the application for them. If it doesn't work, they need to install your application, which they can do by clicking on the link you'll provide. If it does work, then you're all set.
This was a recommended approach for IE by Microsoft support
http://msdn.microsoft.com/en-us/library/ms537503%28VS.85%29.aspx#related_topics
"If you have some control over the binaries being installed on a user’s machine, checking the UA in script seems like a relevant approach:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\5.0\User Agent\Post Platform
" -- By M$ support
Every web page has access to the userAgent string and if you drop a custom post platform value, detecting this in javascript using navigator.userAgent is quite simple.
Fortunately, other major browsers like Firefox and Chrome (barring Safari :( ), do not throw "page not found" errors when a link with a custom protocol is clicked and the protocol is not installed on the users machine. IE is very unforgiving here, any trick to click in a invisible frame or trap javascript errors does not work and ends up with ugly "webpage cannot be displayed" error. The trick we use in our case is to inform users with browser specific images that clicking on the custom protocol link will open an application. And if they do not find the app opening up, they can click on an "install" page. In terms of XD this wprks way better than the ActiveX approach for IE.
For FF and Chrome, just go ahead and launch the custom protocol without any detection. Let the user tell you what he sees.
For Safari, :( no answers yet
I'm trying to do something similar and I just discovered a trick that works with Firefox. If you combine it with the trick for IE you can have one that works on both main browsers (I'm not sure if it works in Safari and I know it doesn't work in Chrome)
if (navigator.appName=="Microsoft Internet Explorer" && document.getElementById("testprotocollink").protocolLong=="Unknown Protocol") {
alert("No handler registered");
} else {
try {
window.location = "custom://stuff";
} catch(err) {
if (err.toString().search("NS_ERROR_UNKNOWN_PROTOCOL") != -1) {
alert("No handler registered");
}
}
}
In order for this to work you also need to have a hidden link somewhere on the page, like this:
<a id="testprotocollink" href="custom://testprotocol" style="display: none;">testprotocollink</a>
It's a bit hacky but it works. The Firefox version unfortunately still pops up the default alert that comes up when you try to visit a link with an unknown protocol, but it will run your code after the alert is dismissed.
You can try something like this:
function OpenCustomLink(link) {
var w = window.open(link, 'xyz', 'status=0,toolbar=0,menubar=0,height=0,width=0,top=-10,left=-10');
if(w == null) {
//Work Fine
}
else {
w.close();
if (confirm('You Need a Custom Program. Do you want to install?')) {
window.location = 'SetupCustomProtocol.exe'; //URL for installer
}
}
}
This is not a trivial task; one option might be to use signed code, which you could leverage to access the registry and/or filesystem (please note that this is a very expensive option). There is also no unified API or specification for code signing, so you would be required to generate specific code for each target browser. A support nightmare.
Also, I know that Steam, the gaming content delivery system, doesn't seem to have this problem solved either.
Here's another hacky answer that would require (hopefully light) modification to your application to 'phone home' on launch.
User clicks link, which attempts to launch the application. A unique
identifier is put in the link, so that it's passed to the
application when it launches. Web app shows a spinner or something of that nature.
Web page then starts checking for a
'application phone home' event from an app with this same unique ID.
When launched, your application does an HTTP post to your web app
with the unique identifier, to indicate presence.
Either the web page sees that the application launched, eventually, or moves on with a 'please download' page.
I have created a custom URL protocol handler.
http://
mailto://
custom://
I have registered a WinForms application to respond accordingly. This all works great.
But I would like to be able to gracefully handle the case where the user doesn't have the custom URL protocol handler installed, yet.
In order to be able to do this I need to be able to detect the browser's registered protocol handlers, I would assume from JavaScript. But I have been unable to find a way to poll for the information. I am hoping to find a solution to this problem.
Thanks for any ideas you might be able to share.
This would be a very, very hacky way to do this... but would this work?
Put the link in as normal...
But attach an onclick handler to it, that sets a timer and adds an onblur handler for the window
(in theory) if the browser handles the link (application X) will load stealing the focus from the window...
If the onblur event fires, clear the timer...
Otherwise in 3-5seconds let your timeout fire... and notify the user "Hmm, looks like you don't have the Mega Uber Cool Application installed... would you like to install it now? (Ok) (Cancel)"
Far from bulletproof... but it might help?
There's no great cross-browser way to do this. In IE10+ on Win8+, a new msLaunchUri api enables you to launch a protocol, like so:
navigator.msLaunchUri('skype:123456',
function()
{
alert('success');
},
function()
{
alert('failed');
}
);
If the protocol is not installed, the failure callback will fire. Otherwise, the protocol will launch and the success callback will fire.
I discuss this topic a bit further here:
https://web.archive.org/web/20180308105244/https://blogs.msdn.microsoft.com/ieinternals/2011/07/13/understanding-protocols/
This topic is of recent (2021) interest; see https://github.com/fingerprintjs/external-protocol-flooding for discussion.
HTML5 defines Custom scheme and content handlers (to my knowledge Firefox is the only implementor so far), but unfortunately there is currently no way to check if a handler already exists—it has been proposed, but there was no follow-up. This seems like a critical feature to use custom handlers effectively and we as developers should bring attention to this issue in order to get it implemented.
There seems to be no straightforward way via javascript to detect the presence of an installed app that has registered a protocol handler.
In the iTunes model, Apple provides urls to their servers, which then provide pages that run some javascript:
http://ax.itunes.apple.com/detection/itmsCheck.js
So the iTunes installer apparently deploys plugins for the major browsers, whose presence can then be detected.
If your plugin is installed, then you can be reasonably sure that redirecting to your app-specific url will succeed.
What seams the most easy solution is to ask the user the first time.
Using a Javascript confirm dialog per example:
You need this software to be able to read this link. Did you install it ?
if yes: create a cookie to not ask next time; return false and the link applies
if false: window.location.href = '/downloadpage/'
If you have control of the program you're trying to run (the code), one way to see if the user was successful in running the application would be to:
Before trying to open the custom protocol, make an AJAX request to a server script that saves the user's intent in a database (for example, save the userid and what he wanted to do).
Try to open the program, and pass on the intent data.
Have the program make a request to the server to remove the database entry (using the intent data to find the correct row).
Make the javascript poll the server for a while to see if the database entry is gone. If the entry is gone, you'll know the user was successful in opening the application, otherwise the entry will remain (you can remove it later with cronjob).
I have not tried this method, just thought it.
I was able to finally get a cross-browser (Chrome 32, Firefox 27, IE 11, Safari 6) solution working with a combination of this and a super-simple Safari extension. Much of this solution has been mentioned in one way or another in this and this other question.
Here's the script:
function launchCustomProtocol(elem, url, callback) {
var iframe, myWindow, success = false;
if (Browser.name === "Internet Explorer") {
myWindow = window.open('', '', 'width=0,height=0');
myWindow.document.write("<iframe src='" + url + "'></iframe>");
setTimeout(function () {
try {
myWindow.location.href;
success = true;
} catch (ex) {
console.log(ex);
}
if (success) {
myWindow.setTimeout('window.close()', 100);
} else {
myWindow.close();
}
callback(success);
}, 100);
} else if (Browser.name === "Firefox") {
try {
iframe = $("<iframe />");
iframe.css({"display": "none"});
iframe.appendTo("body");
iframe[0].contentWindow.location.href = url;
success = true;
} catch (ex) {
success = false;
}
iframe.remove();
callback(success);
} else if (Browser.name === "Chrome") {
elem.css({"outline": 0});
elem.attr("tabindex", "1");
elem.focus();
elem.blur(function () {
success = true;
callback(true); // true
});
location.href = url;
setTimeout(function () {
elem.off('blur');
elem.removeAttr("tabindex");
if (!success) {
callback(false); // false
}
}, 1000);
} else if (Browser.name === "Safari") {
if (myappinstalledflag) {
location.href = url;
success = true;
} else {
success = false;
}
callback(success);
}
}
The Safari extension was easy to implement. It consisted of a single line of injection script:
myinject.js:
window.postMessage("myappinstalled", window.location.origin);
Then in the web page JavaScript, you need to first register the message event and set a flag if the message is received:
window.addEventListener('message', function (msg) {
if (msg.data === "myappinstalled") {
myappinstalledflag = true;
}
}, false);
This assumes the application which is associated with the custom protocol will manage the installation of the Safari extension.
In all cases, if the callback returns false, you know to inform the user that the application (i.e., it's custom protocol) is not installed.
You say you need to detect the browser's protocol handlers - do you really?
What if you did something like what happens when you download a file from sourceforge? Let's say you want to open myapp://something. Instead of simply creating a link to it, create a link to another HTML page accessed via HTTP. Then, on that page, say that you're attempting to open the application for them. If it doesn't work, they need to install your application, which they can do by clicking on the link you'll provide. If it does work, then you're all set.
This was a recommended approach for IE by Microsoft support
http://msdn.microsoft.com/en-us/library/ms537503%28VS.85%29.aspx#related_topics
"If you have some control over the binaries being installed on a user’s machine, checking the UA in script seems like a relevant approach:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\5.0\User Agent\Post Platform
" -- By M$ support
Every web page has access to the userAgent string and if you drop a custom post platform value, detecting this in javascript using navigator.userAgent is quite simple.
Fortunately, other major browsers like Firefox and Chrome (barring Safari :( ), do not throw "page not found" errors when a link with a custom protocol is clicked and the protocol is not installed on the users machine. IE is very unforgiving here, any trick to click in a invisible frame or trap javascript errors does not work and ends up with ugly "webpage cannot be displayed" error. The trick we use in our case is to inform users with browser specific images that clicking on the custom protocol link will open an application. And if they do not find the app opening up, they can click on an "install" page. In terms of XD this wprks way better than the ActiveX approach for IE.
For FF and Chrome, just go ahead and launch the custom protocol without any detection. Let the user tell you what he sees.
For Safari, :( no answers yet
I'm trying to do something similar and I just discovered a trick that works with Firefox. If you combine it with the trick for IE you can have one that works on both main browsers (I'm not sure if it works in Safari and I know it doesn't work in Chrome)
if (navigator.appName=="Microsoft Internet Explorer" && document.getElementById("testprotocollink").protocolLong=="Unknown Protocol") {
alert("No handler registered");
} else {
try {
window.location = "custom://stuff";
} catch(err) {
if (err.toString().search("NS_ERROR_UNKNOWN_PROTOCOL") != -1) {
alert("No handler registered");
}
}
}
In order for this to work you also need to have a hidden link somewhere on the page, like this:
<a id="testprotocollink" href="custom://testprotocol" style="display: none;">testprotocollink</a>
It's a bit hacky but it works. The Firefox version unfortunately still pops up the default alert that comes up when you try to visit a link with an unknown protocol, but it will run your code after the alert is dismissed.
You can try something like this:
function OpenCustomLink(link) {
var w = window.open(link, 'xyz', 'status=0,toolbar=0,menubar=0,height=0,width=0,top=-10,left=-10');
if(w == null) {
//Work Fine
}
else {
w.close();
if (confirm('You Need a Custom Program. Do you want to install?')) {
window.location = 'SetupCustomProtocol.exe'; //URL for installer
}
}
}
This is not a trivial task; one option might be to use signed code, which you could leverage to access the registry and/or filesystem (please note that this is a very expensive option). There is also no unified API or specification for code signing, so you would be required to generate specific code for each target browser. A support nightmare.
Also, I know that Steam, the gaming content delivery system, doesn't seem to have this problem solved either.
Here's another hacky answer that would require (hopefully light) modification to your application to 'phone home' on launch.
User clicks link, which attempts to launch the application. A unique
identifier is put in the link, so that it's passed to the
application when it launches. Web app shows a spinner or something of that nature.
Web page then starts checking for a
'application phone home' event from an app with this same unique ID.
When launched, your application does an HTTP post to your web app
with the unique identifier, to indicate presence.
Either the web page sees that the application launched, eventually, or moves on with a 'please download' page.