How does a desktop application get information back from a website?

Question

I'm a desktop application developer. I'm creating a basic website from which to sell an application I've written, and learning some web tech along the way, but haven't learnt that much yet (my chosen CMS - Textpattern - has saved me learning much PHP so far).

I want my desktop application to call my website and say "I'm version x.x.x.x", and I need it to get back a response - at a minimum "there is/isn't an update", preferably also "it's an xKB download and has these features..." - so that I can display the information to users and ask them if they want to download it.

I can send a request from my app (once I get my head round Qt's QtNetwork module). My question is, what do I need to learn in order to be able to create and send the appropriate response from the website.

I'm fine with learning any necessary new tech/languages, I just want to be sure I'm learning the right stuff and not going down the wrong road. Any help is much appreciated.

Answer 1

HTTP with XML/JSON is a good starting point.

Have your server side respond to an XML/JSON query sent over HTTP.

In your case, it could just well be an XML document just being served by your web server.

Answer 2

The easiest way is to use the HTTP protocol. Pass the app version as a get argument (ie "www.yoursite.com/auto/update.php?version=1.0.2") and the echo something back instead of HTML, eg "up to date" or "new version:1.1.0".

Theres a number of libraries to help you with the desktop side for whatever language and platform your using (not sure if QT includes the HTTP stuff, although I suppose you could just do all the HTTP header stuff yourself).

EDIT: For what the php side does, you could have something simple like

(Hopefully this logic is right, I just came up with it quickly :) )

<?php
    //change this whenever you bring out a new version
    $current_version = array(1, 1, 0);

    $version = $_GET['version'];

    //split the version string into the 3 numeric parts
    $version = split('.', $version);

    //compare $version and $current_version
    if(    $version[0] < $current_version[0]
        || $version[1] < $current_version[1]
        || $version[2] < $current_version[2])
    {
        echo "update_needed, $current_version[0].$current_version[1].$current_version[2]";
    }
    else echo "up_to_date";
?>

Obv if you use a different version string to "x.x.x" then you need to change the code as needed. If you decide to only a single version number, you can replace the array stuff with a single if($version < $current_version).

IF its possible to get a version newer than the current version (eg during testing, beta, etc) then that code may incorrectly report an update (eg if the user had a 2.0.0 test version, and the "offical" version was 1.3.0 then it would say an update was needed because 0 < 3) so you need to change it to handle that, however you hopefully get the idea.

Answer 3

It can be as simple as having your app make a request to

http://website.com/checkupdates.php?v=<current_version>

Your program fills in current_version.

The php script checks to see if there's a new version and responds with information accordingly.

Answer 4

Simplest way to use a webservice is via REST:

Here's a very quick and dirty PHP Script saved as "versioncheck.php" in your server document_root - to simply get the point accross:

<?
define ("CURRENT_VERSION", "5");

$version = $_REQUEST['version'];

if ($version < CURRENT_VERSION) print "Update required";
else print "YOU'RE ALL GOOD";
?>

Your app would call http://wwww.yoursever.com/versioncheck.php?version=2

So let's assume your desktop app has a function called "getHTTP" which can retrieve an HTTP page. And the variable "currentVersion" is your desktop apps current version number.
So your code would be something like this:

//NOTE: I don't know the syntax of your desktop app's language, so just treat this as highlevel pseudo code.

/** all sorts of other goodness **/
//CheckVersion
upgrade = getHTTP("http://wwww.yoursever.com/versioncheck.php?version="+currentVersion); 
if (upgrade == "Update Required") then doUpdate(); // doUPdate is some function you've defined to act as a handler for when an update needs to occur
else
{
... continue on with app ...
}