Safe PHP sessions extension

libSession.php

<?php
 //Drobné rozšíření k PHP sessions
 
 function session_exists($id=false) {
  $sid = '';
  if($id) {
   $sid = $id;
  } elseif(session_id()) {
   $sid = session_id();
  } elseif($_GET['SID']) {
   $sid = $_GET['SID'];
  } elseif($_COOKIE['PHPSESSID']) {
   $sid = $_COOKIE['PHPSESSID'];
  }
  if ($sid) {
   if(!session_id()) {
    session_id($sid);
    session_start();
   }
   if (!$_SESSION['authentic']) {
    session_destroy();
    return false;
   } else {
    return true;
   }
  } else {
   return false;
  }
 }
 
 function session_create($sid=false) {
  if(!$sid){
    $sid = base64_encode(openssl_random_pseudo_bytes(32));
    $sid = str_replace("+", "", $sid);
    $sid = str_replace("/", "", $sid);
    $sid = str_replace("=", "", $sid);
  }
  if(session_id()) {
   session_destroy();
  }
  session_id($sid);
  session_start();
  $_SESSION['authentic'] = true;
 }

 function session_clear() {
  session_start();
  foreach($_SESSION as $key=>$value){
    $_SESSION[$key] = NULL;
  }
  session_destroy();
 }