how to handle expired access tokens facebook PHP sdk - facebook-graph-api

Question

I've read the facbeook blog post about how to handle expired access tokens here: https://developers.facebook.com/blog/post/2011/05/13/how-to--handle-expired-access-tokens/
But a few things are not clear to me and it's making it difficult for me to progress. I've listed both the sample code from the blog, and my own php code. I'd mostly like to know just what changes I need to make to my code so the code from the blog will work in my own. I also have some questions about specific code from the blog. For starters where is $_REQUEST["code"] is coming from?
If you look at my code you'll see that I'm trying to send a notification to a user, I get the app access token before hand, and make the api call that sends the the access token along with it; but in the sample code the graph call gets made with curl_file_get_contents() instead of $facebook->api, what do I do about that? Does $facebook->api return the same kind of response as curl_file_get_contents()? Because the sample code checks that response for errors and redirects if there is one.
//PHP SAMPLE CODE FROM THE BLOG
<?php
$app_id = "YOUR_APP_ID";
$app_secret = "YOUR_APP_SECRET";
//IS THIS SUPPOSED TO BE MY CANVAS APP URL?
$my_url = "YOUR_POST_LOGIN_URL";
// known valid access token stored in a database
$access_token = "YOUR_STORED_ACCESS_TOKEN";
//WHERE IS THIS $CODE VARIABLE COMING FROM?
$code = $_REQUEST["code"];
if (isset($code)) {
$token_url="https://graph.facebook.com/oauth/access_token?client_id="
. $app_id . "&redirect_uri=" . urlencode($my_url)
. "&client_secret=" . $app_secret
. "&code=" . $code . "&display=popup";
$response = file_get_contents($token_url);
$params = null;
parse_str($response, $params);
$access_token = $params['access_token'];
}
// ATTEMPT TO QUERY THE GRAPH
$graph_url = "https://graph.facebook.com/me?"
. "access_token=" . $access_token;
$response = curl_get_file_contents($graph_url);
$decoded_response = json_decode($response);
//CHECK FOR ERRORS
if ($decoded_response->error) {
// check to see if this is an oAuth error:
if ($decoded_response->error->type== "OAuthException") {
// Retrieving a valid access token.
$dialog_url= "https://www.facebook.com/dialog/oauth?"
. "client_id=" . $app_id
. "&redirect_uri=" . urlencode($my_url);
echo("<script> top.location.href='" . $dialog_url
. "'</script>");
}
else {
echo "other error has happened";
}
}
else {
// success
echo("success" . $decoded_response->name);
echo($access_token);
}
// note this wrapper function exists in order to circumvent PHP’s
//strict obeying of HTTP error codes. In this case, Facebook
//returns error code 400 which PHP obeys and wipes out
//the response.
function curl_get_file_contents($URL) {
$c = curl_init();
curl_setopt($c, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($c, CURLOPT_URL, $URL);
$contents = curl_exec($c);
$err = curl_getinfo($c,CURLINFO_HTTP_CODE);
curl_close($c);
if ($contents) return $contents;
else return FALSE;
}
?>
//MY PHP
$token_url ="https://graph.facebook.com/oauth/access_token?" .
"client_id=" . $APP_ID .
"&client_secret=" . $APP_SECRET .
"&grant_type=client_credentials";
$app_token = file_get_contents($token_url);
$app_token = str_replace("access_token=", "", $app_token);
$data = array(
'href'=> 'https://apps.facebook.com/thebringernetwork/',
'access_token'=> $app_token,
'template'=> 'test'
);
// HOW DO I USE THAT ERROR CHECKING CODE AT THIS POINT?
$facebook->api('/16xxxxx3/notifications', 'post', $data);