Simple reliable and non-regex method to unserialize PHP session data

unserialize.php

//
// This is the result of about an hour's delving into PHP's hairy-ass serialization internals.
// PHP provides a session_decode function, however, it's only useful for setting the contents of
// $_SESSION.  Say, for instance, you want to decode the session strings that PHP stores in its
// session files -- session_decode gets you nowhere.
//
// There are a bunch of nasty little solutions on the manual page[1] that use pretty hairy regular
// expressions to get the job done, but I found a simple way to use PHP's unserialize and recurse
// through the string extracting all of the serialized bits along the way.
//
// It's not speedy (it calls unserialize AND serialize for each session element), but it's accurate
// because it uses PHP's internal serialized object parser.  Fun trivia: PHP's serialized object
// parser is an ugly-ass little compiled regular expression engine.  But hey, it works, let's not
// reinvent this wheel.
//
// [1]: http://www.php.net/manual/en/function.session-decode.php
//

define("SESSION_DELIM", "|");

function unserialize_session($session_data, $start_index=0, &$dict=null) {
   isset($dict) or $dict = array();

   $name_end = strpos($session_data, SESSION_DELIM, $start_index);

   if ($name_end !== FALSE) {
       $name = substr($session_data, $start_index, $name_end - $start_index);
       $rest = substr($session_data, $name_end + 1);

       $value = unserialize($rest);      // PHP will unserialize up to "|" delimiter.
       $dict[$name] = $value;

       return unserialize_session($session_data, $name_end + 1 + strlen(serialize($value)), $dict);
   }

   return $dict;
}

$session_data = …; // A string from a PHP session store.

$session_dict = unserialize_session($session_data);