How to check if a user is logged in to facebook - php

Question

I am totally new to facebook api and I wanted to ask , whats the easiest and fastest way to know if a person is logged in to facebook.
One solution that I tought of is to send a javascript or php request and see if i get some status code that tells me whether the person is logged in or not (say if it returns 404, then that means he isnt logged in).
update:
I found this easy "hack":
function logged() {
alert('logged');
}
function notlogged() {
alert('not logged');
}
</script>
<script src="http://www.facebook.com/ajax/composer/attachment/question/question.php" onload="logged()" onerror="notlogged()">
But it doesnt work... however, thats the type of code that i am looking for..code that would send a request and if fails, it will throw an error
**update**
I dont want to trigger any suspicion from the user that I am checking if he is logged in. So if there is a use of app_id, then I would think that I need the users permission to use my app..that is a burden cause I will have to take another authentication step.
I cant have the user know that he is being authenticated in any way regarding facebook

Answer 1

If I am reading your code correctly, only if no session is returned do you do the redirect? According to comments in Facebook's example: http://github.com/facebook/php-sdk/blob/master/examples/example.php (great place to this info huh?), even if you get a session back, you can't assume it's still valid. Only trying an API call that requires a logged in user will you know for sure. This is the best way I've seen to reliably determine login/logout status.
if ($session) {
try {
$me = $facebook->api('/me');
if ($me) {
//User is logged in
}
} catch (FacebookApiException $e) {
//User is not logged in
}
}

Answer 2

try This, Hope this will help
include 'facebook.php';
$facebook = new Facebook(array(
'appId' => $app_id, // your application id
'secret' => $app_secret, // your application secret
'cookie' => false,
));
$user = $facebook->getUser();
$loginUrl = $facebook->getLoginUrl(
array(
'scope' => '// put your permission'
)
);
if ($user) {
try {
// Proceed knowing you have a logged in user who's authenticated.
$permissions = $facebook->api('/me/permissions');
} catch (FacebookApiException $e) {
$user = null;
}
}
if (!$user) {
echo "<script type='text/javascript'>top.location.href = '$loginUrl';</script>";
}

Answer 3

If you have a facebook "tab" then limited user information is provided to you as part of the signed_request. And for a facebook tab, you need to create an app.
Otherwise, without an App ID and alerting the user YOU CANNOT DO IT.
There have been hacks in the past, some of the cleverer ones have been to put up comment boxes and measure the hieght of the containing DIV (they used to be larger if logged in) or to include the facebooks FBML tabs to show a log in button (log in was wider) but theses were all stamped out as they were discovered. The same probably goes for the link you tried in your question.
Facebook, for all the debate on rpivacy, won't knowlingly leak information - until you get an app id, ask the user then you can get nearly everything...

Answer 4

Check this topic: https://stackoverflow.com/a/10698594/1789650
This should answer your question. You have to load the javascript SDK to get it to work correctly.