Related
I'm coding a script in nodejs to automatically retrieve data from an online directory.
Knowing that I had never done this, I chose javascript because it is a language I use every day.
I therefore from the few tips I could find on google use request with cheerios to easily access components of dom of the page.
I found and retrieved all the necessary information, the only missing step is to recover the link to the next page except that the one is generated 4 seconds after loading of page and link contains a hash so that this step Is unavoidable.
What I would like to do is to recover dom of page 4-5 seconds after its loading to be able to recover the link
I looked on the internet, and much advice to use PhantomJS for this manipulation, but I can not get it to work after many attempts with node.
This is my code :
#!/usr/bin/env node
require('babel-register');
import request from 'request'
import cheerio from 'cheerio'
import phantom from 'node-phantom'
phantom.create(function(err,ph) {
return ph.createPage(function(err,page) {
return page.open(url, function(err,status) {
console.log("opened site? ", status);
page.includeJs('http://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js', function(err) {
//jQuery Loaded.
//Wait for a bit for AJAX content to load on the page. Here, we are waiting 5 seconds.
setTimeout(function() {
return page.evaluate(function() {
var tt = cheerio.load($this.html())
console.log(tt)
}, function(err,result) {
console.log(result);
ph.exit();
});
}, 5000);
});
});
});
});
but i get this error :
return ph.createPage(function (page) {
^
TypeError: ph.createPage is not a function
Is what I am about to do is the best way to do what I want to do? If not what is the simplest way? If so, where does my error come from?
If You dont have to use phantomjs You can use nightmare to do it.
It is pretty neat library to solve problems like yours, it uses electron as web browser and You can run it with or without showing window (You can also open developer tools like in Google Chrome)
It has only one flaw if You want to run it on server without graphical interface that You must install at least framebuffer.
Nightmare has method like wait(cssSelector) that will wait until some element appears on website.
Your code would be something like:
const Nightmare = require('nightmare');
const nightmare = Nightmare({
show: true, // will show browser window
openDevTools: true // will open dev tools in browser window
});
const url = 'http://hakier.pl';
const selector = '#someElementSelectorWitchWillAppearAfterSomeDelay';
nightmare
.goto(url)
.wait(selector)
.evaluate(selector => {
return {
nextPage: document.querySelector(selector).getAttribute('href')
};
}, selector)
.then(extracted => {
console.log(extracted.nextPage); //Your extracted data from evaluate
});
//this variable will be injected into evaluate callback
//it is required to inject required variables like this,
// because You have different - browser scope inside this
// callback and You will not has access to node.js variables not injected
Happy hacking!
I am trying to move from events-push:1.0.M7 (latest released official version) to events-push:1.0.0.BUILD-SNAPSHOT. To obtain the latter version I cloned the https://github.com/smaldini/grails-events-push repo and built the plugin locally. The supposed advantage of the later version of the Grails plugin is that it uses newer versions of Atmosphere JavaScript and Java libraries.
In the README file the plugin refers to the GrailsTodos application at https://github.com/smaldini/grailsTodos. However the configuration and the code in the Todos application has nothing in common with the events-push usage information provided in its README file.
Instead, I am trying to use another sample written to demonstrate events-push plugin: https://www.dropbox.com/s/378bqmbu3ad4fnt/GrailsEventsPush.zip. This is an application running in Grails 2.3.7 and using events-push:1.0.M7. It works correctly out of the box with the released version (M7) of the events-push plugin.
Here are the steps I made to make it compile and run with events-push:1.0.0.BUILD-SNAPSHOT (which I installed locally using 'grails maven-install'):
In BuildConfig.groovy
grails.servlet.version = "3.0"
grails.tomcat.nio = true
...
dependencies {
compile 'org.grails.plugins:events:1.0.0.BUILD-SNAPSHOT'
}
plugins {
...
//compile ":events-push:1.0.M7"
compile ":events-push:1.0.0.BUILD-SNAPSHOT"
}
In MyEvents.groovy
events = {
'bagsUpdated' namespace: 'browser', browser:true // allows browser push on this topic
}
In the EventTestingController:
def updateBags() {
Thread.sleep(3000)
event([namespace: 'browser', topic: 'bagsUpdated']) // will trigger registered browsers on 'bagsUpdated' topic
render "OK"
}
I did not change index.gsp:
<script type="text/javascript">
try {
var grailsEvents = new grails.Events("${createLink(uri:'')}", {transport: "sse"});
grailsEvents.on('bagsUpdated', function (data) {
window.console && console.log("GOT bags!");
$("#waiting").html("Event fired!");
});
} catch (error) {
console.log("ERROR: " + error.toString());
}
$(function () {
// Call controller method that emits event when its done
$.ajax({
url: "${createLink(action:'updateBags')}",
success: function () {
console.log("Event should have been already fired...");
},
error: function () {
console.log("Ops something went wrong... ");
}
});
});
</script>
The code that worked correctly with 1.0.M7 version of the plugin does not work with 1.0.0.BUILD-SNAPSHOT version. Here is what I see in the Chrome console:
defer connecting topic: eventsbus grailsEvents.js:108
defer connecting topic: bagsUpdated grailsEvents.js:108
XHR finished loading: POST "http://localhost:8080/GrailsEventsPush/g-eventsbus/eventsbus?X-Atmosphere-t…sport=polling&X-Cache-Date=0&Content-Type=application/json&_=1416503898595". jquery.atmosphere.js:1691
XHR finished loading: POST "http://localhost:8080/GrailsEventsPush/g-eventsbus/eventsbus?X-Atmosphere-t…sport=polling&X-Cache-Date=0&Content-Type=application/json&_=1416503898598". jquery.atmosphere.js:1691
XHR finished loading: GET "http://localhost:8080/GrailsEventsPush/eventTesting/updateBags". jquery-1.11.0.min.js:4
Event should have been already fired... index:32
There are no errors - the browser simply does not get the event fired by the controller, which would produce "GOT bags!" and "Event fired!" statements in the Console.
The application I am trying to upgrade exhibits the same behavior - the server side events do not reach the browser. What am I missing?
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 am trying to run a casper test for an internal site. Its running on pre-production environment, the code so far is
var casper = require('casper').create({
verbose: true,
loglevel:"debug"
});
// listening to a custom event
casper.on('page.loaded', function() {
this.echo('The page title is ' + this.getTitle());
this.echo('value is: '+ this.getElementAttribute
('input[id="edit-capture-amount"]',
'value'));
});
casper.start('https://preprod.uk.systemtest.com', function() {
this.echo(this.getTitle());
this.capture('frontpage.png');
// emitting a custom event
this.emit('age.loaded.loaded');
});
casper.run();
as you can see its not much but my problem is the address is not reachable. The capture also shows a blank page. Not sure what i am doing wrong. I have checked the code with cnn and google urls, the title and screen capture works fine. Not sure how to make it work for an internal site.
I had the exact same problem. In my browser I could resolve the url, but capserjs could not. All I got was about::blank for a web page.
Adding the --ignore-ssl-errors=yes worked like a charm!
casperjs mytestjs //didn't work
capserjs --ignore-ssl-errors=yes mytestjs //worked perfect!
Just to be sure.
Can you reach preprod.uk.systemtest.com from the computer on which casper runs ? For example with a ping or wget.
Is there any proxy between your computer and the preprod server ? Or is your system configured to pass through a proxy that should not be used for the preprod server ?
The casper code seems to be ok.
I know this should be a comment but I don't have enough reputation to post a comment.
As far as CasperJs tests are run in localhost, for testing a custom domain/subdomain/host, some headers need to be defined.
I experienced some problems when passing only the HOST header, for instance, snapshots were not taken properly.
I added 2 more headers and now my tests run properly:
casper.on('started', function () {
var testHost = 'preprod.uk.systemtest.com';
this.page.customHeaders = {
'HOST': testHost,
'HTTP_HOST': testHost,
'SERVER_NAME': testHost
};
});
var testing_url: 'http://localhost:8000/app_test.php';
casper.start(_testing_url, function() {
this.echo('I am using symfony, so this should have to show the homepage for the domain: preprod.uk.systemtest.com');
this.echo('An the snapshot is also working');
this.capture('casper_capture.png');
}
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.