Facebook PHP SDK doesn't work through AJAX - php

Question

The situation: I have a finished Facebook canvas app (PHP/CodeIgniter), I just need to add the Facebook-related options such as sharing and inviting friends.
Current task: getting the list of invitable friends from the PHP SDK.
Relevant documentation: https://developers.facebook.com/docs/games/invitable-friends/v2.0
The code: in my Facebook library, I have created the following function.
/**
* Returns the current user's invitable friends
*/
public function get_invitable_friends() {
if ( $this->session ) {
$request = ( new FacebookRequest( $this->session, 'GET', '/me/invitable_friends' ) )->execute();
$graphObject = $request->getGraphObject();
return $graphObject;
}
return false;
}
The condition if($this->session) is because it doesn't make sense to try anything if there's no Facebook session in the first place. This will come into play later.
I've tried calling this function in two ways. The first way works and the second doesn't. I'm gonna present both, and then somebody will hopefully explain to me why the second way doesn't work and how to fix it, as I'd much prefer to use that.
First (working) way:
Call the function from the main controller's index() method, as the page loads. The function correctly returns a list of my friends.
Second (non-working) way:
Create this function in the controller:
//load list of friends we can invite to play the game
public function load_invitable_friends()
{
$this->load->library('facebook');
$list = $this->facebook->get_invitable_friends();
var_dump($list);
}
Then call it through AJAX, like:
function loadInvites(){
$.post(base+"main/load_invitable_friends/",function(resp){
$('#slide_6_inner').html(resp);
});
}
After this call, the content of the slide_6_inner div should contain the list of friends, as dumped by var_dump. However, the content is bool(false), indicating that the Facebook session is no longer present.
If I remove the condition if( $this->session ) from the get_invitable_friends() method, then this error happens:
A PHP Error was encountered
Severity: 4096
Message: Argument 1 passed to Facebook\FacebookRequest::__construct() must be an instance of Facebook\FacebookSession, null given, called in /home/lights/public_html/appname/application/libraries/facebook/Facebook.php on line 125 and defined
Filename: Facebook/FacebookRequest.php
Line Number: 182
The session in Facebook.php is initially created with the following code.
$this->ci =& get_instance();
// Initialize the SDK
FacebookSession::setDefaultApplication( $api_id, $api_secret) );
$this->helper = new FacebookCanvasLoginHelper();
$this->session = $this->helper->getSession();
To sum up - why is this problem occurring and how do I fix it?

Answer 1

In order to retrieve the session from the server side, you will need to first create a session using the FacebookCanvasLoginHelper. This class takes a signed request from Facebook supplied in a POST request, and exchanges it for a FacebookSession object. This should only really be done one when a user logs into your application:
$helper = new FacebookCanvasLoginHelper();
try {
$session = $helper->getSession();
} catch (FacebookRequestException $ex) {
// When Facebook returns an error
} catch (\Exception $ex) {
// When validation fails or other local issues
}
if ($session) {
// Store this in your PHP session somewhere:
$token = $session->getToken();
}
Thereafter, you should use the token to initialize the session:
$token = //GET THIS FROM SESSION
use Facebook\FacebookSession;
FacebookSession::setDefaultApplication('app-id', 'app-secret');
// If you already have a valid access token:
$session = new FacebookSession($token);
// To validate the session:
try {
$session->validate();
} catch (FacebookRequestException $ex) {
// Session not valid, Graph API returned an exception with the reason.
echo $ex->getMessage();
} catch (\Exception $ex) {
// Graph API returned info, but it may mismatch the current app or have expired.
echo $ex->getMessage();
}

Answer 2

Well, it seems you are not doing anything if session does not exists, just returning false. The problem is occuring because the session is expired/or does not exists, so you have to validate the fbToken and set the session again or create a new one.
You can create a function that checks if user is logged in, like:
function CheckFbUser() {
// Check if existing session exists
if (isset($_SESSION) && isset($_SESSION['fb_token'])) {
// Create new session from saved access_token
$session = new FacebookSession($_SESSION['fb_token']);
// Validate token
try {
if (!$session->validate()) {
$session = null;
}
} catch (Exception $e) {
// Catch any exceptions
$session = null;
}
} else {
// No session
try {
$session = $helper->getSessionFromRedirect();
} catch(FacebookRequestException $e) {
// handle it for facebook exceptions
} catch(Exception $e) {
// handle your php exceptions
}
}
// Check if a session exists
if ( isset( $session ) ) {
// Save the session
$_SESSION['fb_token'] = $session->getToken();
// Create session using saved token or the new one we generated at login
$session = new FacebookSession( $session->getToken() );
// USUALLY, here, people show the Logout Button, or anything alike, but you could it
// to return true, and then continue to run your code.
} else {
// No session
// USUALLY, here, people show the Login Button, or anything alike, you could
// use it to return false, or redirect user to login first.
$helper->getLoginUrl();
}
}
That is just an simple code, to check if user is logged in or not before you run the requests.