Description:
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After switching webservers (and upgrading PHP) over the weekend for an internal application, our users began reporting that they were getting logged out randomly. After triple-checking our code and web server setup, we started digging through the PHP source, and eventually discovered the issue.

In PHP 4.3.4 (and versions before and after 4.3.4), setting a nonzero value of session.cookie_lifetime either via php.ini or session_set_cookie_params() resulted in a cookie that expires a certain number of seconds after the current page load. This has the net effect of session.cookie_lifetime setting an inactivity timeout.

In PHP 4.3.11, session_start() sends Set-Cookie: once, with an expiration time governed by session.cookie_lifetime. (I believe this behavior changed for PHP 4.3.9.) So, if session.cookie_lifetime is 20 minutes, the cookie will expire and destroy the session 20 minutes after login, regardless of any activity.

Bug #30232 attempted to change this behavior and got a patch committed, but it was ripped out, saying that the behavior of setting the cookie once is intentional and correct. I feel that this behavior is completely wrong for cases where session.cookie_lifetime is nonzero; there is no situation where sessions should expire a fixed time after setting them, but many situations where sessions should expire a fixed time after a call to session_start().

My proposed fix is to always send cookies if session.cookie_lifetime is nonzero.

Reproduce code:
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<?php

header('Refresh: 10');
session_set_cookie_params(15);
session_start();

if (!isset($_SESSION['i'])) {
  $_SESSION['i'] = 1;
  echo 'Started session.';

} else {
  $_SESSION['i']++;
  echo "Page load number {$_SESSION['i']}.";
}


Expected result:
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"Page load number" should keep incrementing for as long as the browser keeps refreshing the page within the cookie lifetime.

Actual result:
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The cookie expires 15 seconds after the first page load, destroying the session.