public static function get_chat_users($chatsid) {
        global $DB, $PAGE;

        $params = self::validate_parameters(self::get_chat_users_parameters(),
                                            array(
                                                'chatsid' => $chatsid
                                            ));
        $warnings = array();

        // Request and permission validation.
        if (!$chatuser = $DB->get_record('chat_users', array('sid' => $params['chatsid']))) {
            throw new moodle_exception('notlogged', 'chat');
        }
        $chat = $DB->get_record('chat', array('id' => $chatuser->chatid), '*', MUST_EXIST);
        list($course, $cm) = get_course_and_cm_from_instance($chat, 'chat');

        $context = context_module::instance($cm->id);
        self::validate_context($context);

        require_capability('mod/chat:chat', $context);

        // First, delete old users from the chats.
        chat_delete_old_users();

        $users = chat_get_users($chatuser->chatid, $chatuser->groupid, $cm->groupingid);
        $returnedusers = array();

        foreach ($users as $user) {

            $userpicture = new user_picture($user);
            $userpicture->size = 1; // Size f1.
            $profileimageurl = $userpicture->get_url($PAGE)->out(false);

            $returnedusers[] = array(
                'id' => $user->id,
                'fullname' => fullname($user),
                'profileimageurl' => $profileimageurl
            );
        }

        $result = array();
        $result['users'] = $returnedusers;
        $result['warnings'] = $warnings;
        return $result;
    }