cookie.php

<?php

header('Content-Type: text/html; charset=Shift_JIS');
// header('Content-Type: text/x-hdml; charset=Shift_JIS');

session_name('_normal');
session_start();

$host = $_SERVER['HTTP_HOST'];
if ($_pos = strpos($host, ':'))
{
  $host = substr($host, 0, $_pos);
}

$is_ssl = false;
if (isset($_SERVER['HTTPS']) && 'on' === $_SERVER['HTTPS'])
{
  $is_ssl = true;
}

if (isset($_GET['mode']))
{
  $mode = $_GET['mode'];
  if ('login' === $mode)
  {
    $_SESSION['user_name'] = '太郎';
    $sid = session_id();
    if ($is_ssl)
    {
      header('Location: http://'.$host.'/cookie.php?mode=setlogin&sid='.$sid);
      exit;
    }
    else
    {
      header('Location: https://'.$host.'/cookie.php?mode=setlogin&sid='.$sid);
      exit;
    }
  }
  elseif ('logout' === $mode)
  {
    session_destroy();

    if ($is_ssl)
    {
      header('Location: http://'.$host.'/cookie.php?mode=setlogout');
      exit;
    }
    else
    {
      header('Location: https://'.$host.'/cookie.php?mode=setlogout');
      exit;
    }
  }
  elseif ('setlogin' === $mode)
  {
    session_write_close();

    session_id($_GET['sid']);
    session_start();
    if ($is_ssl)
    {
      header('Location: http://'.$host.'/cookie.php');
      exit;
    }
    else
    {
      header('Location: https://'.$host.'/cookie.php');
      exit;
    }
  }
  elseif ('setlogout' === $mode)
  {
    session_destroy();

    if ($is_ssl)
    {
      header('Location: http://'.$host.'/cookie.php');
      exit;
    }
    else
    {
      header('Location: https://'.$host.'/cookie.php');
      exit;
    }
  }
}

$username = '名無し';
if (isset($_SESSION['user_name']))
{
  $username = $_SESSION['user_name'];
}

?>
<?php if (!isset($_GET['mode'])): ?>
<?php echo mb_convert_encoding('ようこそ '.$username.'さん！', 'Shift-JIS', 'UTF-8') ?> <br><br>
ADDR: <?php echo $_SERVER['REMOTE_ADDR']; ?><br>
PORT: <?php echo $_SERVER['SERVER_PORT']; ?><br>
<br>
<a href="./cookie.php?mode=login">login</a><br>
<a href="./cookie.php?mode=logout">logout</a><br>
<?php endif; ?>
<a href="./cookie.php">Reload</a><br>
<br>
<a href="http://<?php echo $host ?>/cookie.php">HTTP</a><br>
<a href="https://<?php echo $host ?>/cookie.php">HTTPS</a><br>

It's too complicated for understanding. You are included so much code under PHP cookies. Management is important for PHP cookies and PHP session. You need more clarification.