Why does this PHP header() redirect get stuck in an infinite loop?

I have this piece of code that is supposed to get the current date, comapre it to a set end date, and redirect if the current date is past the end date. Whenever I set the $promoend to a past date, I get stuck in a redirect loop.

The if() block should only redirect if the promotion has ended and I am not on the closed.php page already.

$currentdate = new DateTime("now");
$promoend = new DateTime("11/01/2010 00:00:00");
$promoend = $currentdate->diff($promoend)->invert;
if ($promoend && !strpos($_SERVER["PHP_SELF"],"closed.php")) {
    header("Location: ".$environment->root."/closed.php");
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Any idea why this is caught in a loop?

strpos can return 0 if the needle ('closed.php') is at the start of the haystack ($_SERVER['PHP_SELF']). This will get treated as 'false' by PHP, as you're not using a strict comparison operator.

You MUST use the strict comparison operator to check for this case:

if ($promoend && (strpos(...) !== FALSE)) {
   header(...);
}

if ($promoend && !strpos($_SERVER["PHP_SELF"],"closed.php")) {
    header("Location: ".$environment->root."/closed.php");
}

...should probably be...

if ($promoend && strpos($_SERVER["PHP_SELF"],"closed.php")!==true) {
    header("Location: ".$environment->root."/closed.php");
}

Because strpos() does not always return a boolean so you have to use the PHP equivalence operator.

Assuming your date calculations are correct the reason is, is that strpos is returning 0 because the string you are looking for in PHP_SELF is at the 0 position.

You have to use !== "" instead of just !val because 0 is the same as "" is the same as NULL