Detecting if a user has left the site

LazyManc · 14 May 2007 at 09:12

I have a reservation system that currently reserves tickets for 5 minutes, after which they get released. Unfortunately this is still causing problems as users may browse away from the site or close their browser window leaving those reservations locked until the time-out. I could reduce the time-out but this would be a problem for users who are still completing a form or whatever on the site.

Basically I'm asking if there is a reliable way to detect if a user has left the site, either by browsing to another domain or closing their browser window?

I was thinking of calling the ticket release function with an ajax call from the browsers onunload event, but that would mean that it would be called even if they were just browsing between pages on my site.

Is there a way of getting the next url to be loaded from within the onunload call? I guess adding an ajax call for every page unload is going to be an additional strain on the server... probably a bad idea all-round.

Shoseki · 14 May 2007 at 13:26

There is a javascript event handler called onUnload which could be attached to the Body tag... as long as they have javascript switched on...

JamesU2005 · 14 May 2007 at 13:29

PHP Sessions?

roboffer · 14 May 2007 at 13:59

What technology?

If its ASP or .NET you could use the Session_End event thorugh the Global.asa(x) file.

LazyManc · 14 May 2007 at 16:39

platform = PHP/MYSQL

Ideally i'd be able to test client side for a change in domain and then fire off the ajax request as the last thing the browser does before it moves to the new site.

It doesn't have to be 100% reliable because the reservations are released after a timeout by default, but the quicker they are released the better.

The browser wouldn't have to wait for a response because there's nothing to send back to it, it's purely a server-side action.

Dj_Jestar · 14 May 2007 at 16:44

Can't be done. Manage your sessions better.

Jaffa_Cake · 14 May 2007 at 17:25

I do this for a web based chat thingy. It has a userlist thats acurate to 5 seconds using ajax.

Code:

$query = "SELECT * FROM `jaf_activity` WHERE `sid` = " . $sql->safe(session_id());
$result = $sql->query($query);
$row = mysql_fetch_array($result, MYSQL_ASSOC);
	if ($row['sid'] == session_id()) {
		$query = "UPDATE `jaf_activity` SET `time` = " . $sql->safe(time()) . ", `name` = " . $sql->safe($_GET['u']) . ", `ip` = " . $sql->safe($_SERVER['REMOTE_ADDR']) . " WHERE `sid` = " . $sql->safe(session_id());
		$sql->query($query);
	} else {
		$query = "INSERT INTO `jaf_activity` (`id`, `name`, `sid`, `time`, `ip`) VALUES (NULL, " . $sql->safe($_GET['u']) . ", " . $sql->safe(session_id()) . ", " . $sql->safe(time()) . ", " . $sql->safe($_SERVER['REMOTE_ADDR']) . " ) ";
		$sql->query($query);
	}

Ajax sends requests a to a file with this code in every 4 seconds, doesn't receive any response so it barly lags the user. Keeps an activity log within a couple of seconds.

Please tell me if i have said something stupid im having a bad day :eek:

P.S. Note that codes taken straight of a framework and so will need adjusting a lil bit.

Edit: I just saw your bit about ajax. You don't actually have to send any header response. You will receive 4 header lines every couple of seconds. Creates next to no strain

lookitsjonno · 14 May 2007 at 17:47

theres no clean way of doing it unfortunately, it's one of the restrictions of the http protocol.

dirty (and resource heavy) ways to achieve it include ajax (as above, requires javascript) and a hidden iframe with some sort of meta refresh.

Beansprout · 14 May 2007 at 18:12

You've got a 5 minute timeout that works....easy peasy

Jaffa_Cake · 14 May 2007 at 18:19

Beansprout said:
You've got a 5 minute timeout that works....easy peasy

Or you could do a ajax loop every 2 minutes. Not exactly resource heavy.

I just love ajax

Dj_Jestar · 15 May 2007 at 09:28

A classic case of "I'm using AJAX Because it's fashionable!"

LazyManc · 15 May 2007 at 10:56

Jaffa_Cake said:
Or you could do a ajax loop every 2 minutes. Not exactly resource heavy.

I just love ajax

Maybe not on a low-usage site but if you're serving 10k+ visitors an hour during peak times then it's a different kettle of fish.

I guess I'll just have to reduce the timeout on the reservations to 3 minutes.

Jaffa_Cake · 15 May 2007 at 11:48

Dj_Jestar said:
A classic case of "I'm using AJAX Because it's fashionable!"

That is very true :eek:

It does add a new level of interactivity to web based forms which I do like.

toosepin · 15 May 2007 at 12:00

Jaffa_Cake said:
That is very true

It does add a new level of interactivity to web based forms which I do like.

And it can be soo pwetty!

Dj_Jestar · 15 May 2007 at 12:24

and completely ruin the fundamentals of usability just because it "ajax", and add extra workload to your web applications infrastructure, just because it's "ajax."

Shoseki · 15 May 2007 at 15:35

It also cleans floors really well...

EDIT : Bizarre trivia : When I saw the Ajax adverts when I was a kid (in the 80s) I got it into my head that the real name for the product was "Xaja Diuqil" because of the reflection in a well cleaned tile...

Mr^B · 15 May 2007 at 16:15

Shoseki said:
It also cleans floors really well...

EDIT : Bizarre trivia : When I saw the Ajax adverts when I was a kid (in the 80s) I got it into my head that the real name for the product was "Xaja Diuqil" because of the reflection in a well cleaned tile...

"diuqiL xajA" surely?

Conrad11 · 15 May 2007 at 19:04

Sorry to interrupt whatever is going on, but could someone link me to a good example of an Ajax enabled site please?

Dj_Jestar · 15 May 2007 at 19:05

lightbox gallery sites.

Conrad11 · 15 May 2007 at 19:06

Dj_Jestar said:
lightbox gallery sites.

Ah i see the picture now (in more ways that one)

Thanks.