header('location:index.php') doesn't work in the first run

Question

I have an index.php page that a session is set inside($_SESSION['expire']). This session should be unset after 30 mins and we should redirect to index.php (to verify the user again).

some part of my index.php code:

<?php
session_start();
//if user name and password are valid do the following:
$_SESSION['start'] = time(); 
$_SESSION['expire'] = $_SESSION['start'] + (30 * 60) ;
?>

<a href="index.php?action=ContentManager">
    content 
</a>

<?php    
if(isset($_REQUEST['action']))

{
    //if the expiration time has not reached yet do the following
    $now=time();
    if (isset($_SESSION['expire']) && ($now<= $_SESSION['expire'])) 
    {
        switch($_REQUEST['action'])
        {
            case 'ContentManager' : 
              include('model/content.php');
              $contents = getContent($conn, ' where 1=1');
              include('view/contentmanager.php');
              break;
        }
    }

    else if($now > $_SESSION['expire'])
    {
        unset($_SESSION['expire']);
        session_destroy();
        header('location:index.php');
       exit();
    }   
}
?>

the problem is that when I click contentmanager link after 30 mins, we will redirect to an empty page with url: index.php?action=contentmanager

And only if I refresh the page again, we will redirect to index.php itself and the login form will be appeared.

So breifly: I have to refresh the page two times to redirect to the correct page.

Thanks in advance

Answer 1

use ob_start();

<?php
session_start();
ob_start();
//if user name and password are valid do the following:
$_SESSION['start'] = time(); 
$_SESSION['expire'] = $_SESSION['start'] + (30 * 60) ;
?>

<a href="index.php?action=ContentManager">
    content 
</a>

<?php    
if(isset($_REQUEST['action']))

{
    //if the expiration time has not reached yet do the following
    $now=time();
    if (isset($_SESSION['expire']) && ($now<= $_SESSION['expire'])) 
    {
        switch($_REQUEST['action'])
        {
            case 'ContentManager' : 
              include('model/content.php');
              $contents = getContent($conn, ' where 1=1');
              include('view/contentmanager.php');
              break;
        }
    }

    else if($now > $_SESSION['expire'])
    {
        unset($_SESSION['expire']);
        session_destroy();
        header('location:index.php');
       exit();
    }   
}
ob_end_flush();
?>