Return true or false from readAttribute if $attr is empty

This way, readAttribute can act as an existence checker.

apps/user_ldap/lib/access.php

@@ -40,9 +40,10 @@ abstract class Access {
 	 * @brief reads a given attribute for an LDAP record identified by a DN
 	 * @param $dn the record in question
 	 * @param $attr the attribute that shall be retrieved
-	 * @returns the values in an array on success, false otherwise
+	 *        if empty, just check the record's existence
+	 * @returns true or the values in an array on success, false otherwise
 	 *
-	 * Reads an attribute from an LDAP entry
+	 * Reads an attribute from an LDAP entry or check if entry exists
 	 */
 	public function readAttribute($dn, $attr, $filter = 'objectClass=*') {
 		if(!$this->checkConnection()) {
@@ -57,10 +58,14 @@ abstract class Access {
 		}
 		$rr = @ldap_read($cr, $dn, $filter, array($attr));
 		if(!is_resource($rr)) {
-			\OCP\Util::writeLog('user_ldap', 'readAttribute '.$attr.' failed for DN '.$dn, \OCP\Util::DEBUG);
+			\OCP\Util::writeLog('user_ldap', 'readAttribute failed for DN '.$dn, \OCP\Util::DEBUG);
 			//in case an error occurs , e.g. object does not exist
 			return false;
 		}
+		if (empty($attr)) {
+			\OCP\Util::writeLog('user_ldap', 'readAttribute: '.$dn.' found', \OCP\Util::DEBUG);
+			return true;
+		}
 		$er = ldap_first_entry($cr, $rr);
 		if(!is_resource($er)) {
 			//did not match the filter, return false

apps/user_ldap/user_ldap.php

@@ -149,9 +149,8 @@ class USER_LDAP extends lib\Access implements \OCP\UserInterface {
 			return false;
 		}
 
-		//if user really still exists, we will be able to read his objectclass
-		$objcs = $this->readAttribute($dn, 'objectclass');
-		if(!$objcs || empty($objcs)) {
+		//check if user really still exists by reading its entry
+		if(!$this->readAttribute($dn, '') ) {
 			$this->connection->writeToCache('userExists'.$uid, false);
 			return false;
 		}