Can header() redirects be counted on to end the program flow?

Question

In a PHP program can header() redirects be counted on to end the program flow, or is there value in, for example, following them with a die() to be safe? Is it possible for the user to exploit the script by somehow forgoing the redirects? This question is crucial in a case where the user is redirected for not having sufficient access permissions and the code following is intended only for those who were not redirected.

Answer 1

No, header do not end the program execution. You must end it yourself with exit or die. You can try this yourself with something like this:

<?php
file_put_contents('/tmp/test', '1');
header('Location: http://www.emilvikstrom.se/');
file_put_contents('/tmp/test', '2');
?>

Check the content of /tmp/test and you'll find that it is 2.

I've also tried this script:

<?php
header('Location: http://www.emilvikstrom.se/');
echo "Test\n";
?>

together with telnet to send a manual HTTP request, with this result:

HTTP/1.1 302 Found
Server: nginx/0.7.67
Date: Tue, 05 Jul 2011 07:27:14 GMT
Content-Type: text/html
Connection: close
X-Powered-By: PHP/5.3.3-7+squeeze1
Location: http://www.emilvikstrom.se/
Vary: Accept-Encoding
Content-Length: 5

Test

As you see, everything which is echoed after the Location header is still sent to the browser. In fact, PHP cannot know after a header call if you are going to send it more headers, or if the things you echo out are of importance.