Remember me for PHP (& Mongo)

rememberme.php

define('REMEMBER_TIMEOUT',time()+60*60*24*2);
define('REMEMBER_SALT','secretword');
define('REMEMBER_COOKIE','some_cookie_name');

function remember_me($set=false, $username='')
{
        $db = mongo();

        // Set the cookie and add the db record
        if($set)
        {
                $hash = md5(($_SERVER['REMOTE_ADDR']?$_SERVER['REMOTE_ADDR']:rand().time()).$username.REMEMBER_SALT);
                setcookie(REMEMBER_COOKIE,$hash,REMEMBER_TIMEOUT);

                // Add the record
                $db->remember->insert(array(
                        'user' => $_SESSION['user']['_id'],
                        'hash' => $hash,
                        'timeout' => REMEMBER_TIMEOUT
                ));
        }
        // Just attempt to read the value
        else if(isset($_COOKIE[REMEMBER_COOKIE]) && !isset($_SESSION['user']))
        {
                $remember = $db->remember->findOne(array(
                        'hash' => $_COOKIE[REMEMBER_COOKIE]
                ));
                if($remember)
                {
                        // Get the user's record
                        $user = $db->user->findOne(array(
                                '_id' => new MongoId($remember['user'])
                        ));
                        $remember['timeout'] = REMEMBER_TIMEOUT;
                        $db->remember->save($remember);
                        $_SESSION['user'] = $user;
                }
        }
}

...

// After session_start at the start of your script
remember_me();

...

// During login post
if($_POST['remember_me'])
{
        remember_me(true,$user['username']);
}