PHP referer url和重定向

Question

I can't seem to work out why the below sends ALL traffic to the page-not-found page, even if referred by Paypal. Any ideas?

$refererUrl = $_SERVER['HTTP_REFERER'];
$Exploded = explode("/",$refererUrl);
$urlToCheck = $Exploded[3];
$findURL = strpos($urlToCheck,'paypal.com');
if($findURL === false){
    header('location:/page-not-found');
} else  {
/* Do something if page referred to by Paypal */
}

Answer 1

You are checking if 'paypal.com' is present in $Exploded[3]. Why do you expect that part of the referer url to be the hostname? Array indexes start at 0, so counting from left to right would give you the following, indicating that 2 would be the correct index.

$Exploded = explode('http://www.google.com/?q=foobar', '/');

// $Exploded now contains:
0: http:
1: 
2: www.google.com
3: ?q=foobar

However, it would be more safe to use some utility that will parse arbitrary URLs and read the hostname from the interpreted url. You could do something like this (untested):

$referer = parse_url($_SERVER['HTTP_REFERER']);
if($referer['host'] != 'paypal.com')
    header('location:/page-not-found');
else
    /* Do something if page referred to by Paypal */

parse_url doc: http://php.net/manual/en/function.parse-url.php