Google drive API with service account is not working - php

Question

I am trying to implement google drive api with my service account .
Warning: file_get_contents() [function.file-get-contents]:
Filename cannot be empty in /home/logic5nv/public_html/projects/
google_drive /gservice.php on line 18
Fatal error: Uncaught exception 'Google_AuthException' with message
require_once "google-api-php-client/src/Google_Client.php";
require_once "google-api-php-client/src/contrib/Google_DriveService.php";
require_once "google-api-php-client/src/contrib/Google_Oauth2Service.php";
session_start();
$DRIVE_SCOPE = 'https://www.googleapis.com/auth/drive';
$SERVICE_ACCOUNT_EMAIL =
'842613324525-6veubhkhrurplpshiuagmdvk1rtm1q1g#developer.gserviceaccount.com';
$SERVICE_ACCOUNT_PKCS12_FILE_PATH = '8447ce76bbb4956f9cbecd6779371ad3ab8f8e7e-
privatekey.p12';
function buildService() {
$key = file_get_contents($SERVICE_ACCOUNT_PKCS12_FILE_PATH);
$auth = new Google_AssertionCredentials(
SERVICE_ACCOUNT_EMAIL,
array(DRIVE_SCOPE),$key);
$client = new Google_Client();
$client->setUseObjects(true);
$client->setAssertionCredentials($auth);
return new Google_DriveService($client);
}
$service = buildService();
$file = new Google_DriveFile();
$file->setTitle('My document');
$file->setDescription('A test document');
$file->setMimeType('text/plain');
$data = file_get_contents('document.txt');
$createdFile = $service->files->insert($file, array(
'data' => $data,
'mimeType' => 'text/plain',
));
print_r($createdFile);

Answer 1

Try :
function buildService() {
global $SERVICE_ACCOUNT_PKCS12_FILE_PATH,$SERVICE_ACCOUNT_EMAIL,$DRIVE_SCOPE ;
$key = file_get_contents($SERVICE_ACCOUNT_PKCS12_FILE_PATH);
$auth = new Google_AssertionCredentials(
SERVICE_ACCOUNT_EMAIL,
array(DRIVE_SCOPE),$key);
$client = new Google_Client();
$client->setUseObjects(true);
$client->setAssertionCredentials($auth);
return new Google_DriveService($client);
}