session_set_save_handler causing login loop

I'm trying to write sessions to database using session_set_save_handler(). I'm getting an infinite loop, where my system wants to log me in, but cannot find the session, so it logs me out... but the session exists apparently - just not in the table.

Anyway, here's my code for the session functions - I don't think there's anything wrong here:

<?php

// session.functions.php

$db = new mysqli("127.0.0.1", "user", "pass", "db");
// define 'openSession()' function
function openSession($sessionPath, $sessionName) {
    return true;
}

// define 'closeSession()' function
function closeSession() {
    return true;
}

// define 'readSession()' method
function readSession($sessionId) {
    global $db;
    // escape session ID
        $sessionId = $db->real_escape_string($sessionId);
    $result = $db->query("SELECT sessiondata FROM sessions WHERE
sessionid='$sessionId' AND expiry > NOW()");
    if ($result->num_rows > 0) {
        $row = $result->fetchRow();
        return $row['sessiondata'];
    }
    // return empty string
    return "";
}

// define 'writeSession()' function
function writeSession($sessionId, $sessionData) {
    global $db;
    $expiry = time() + get_cfg_var('session.gc_maxlifetime') - 1;
    // escape session ID & session data
        $sessionId = $db->real_escape_string($sessionId);
        $sessionData = $db->real_escape_string($sessionData);
    $result = $db->query("SELECT sessionid FROM sessions WHERE
sessionid='$sessionId'");
    // check if a new session must be stored or an existing one must be updated 
    ($result->num_rows > 0) ? $db->query("UPDATE sessions SET     sessionid='$sessionId',expiry='$expiry',sessiondata=
'$sessionData' WHERE sessionid='$sessionId'") or die(mysqli_error($db)) : $db->query("INSERT INTO sessions (sessionid,expiry,sessiondata) VALUES ('$sessionId','$expiry','$sessionData')") or die(mysqli_error($db));
    return true;
}

// define 'destroySession()' function
function destroySession($sessionId) {
    global $db;
    // escape session ID
        $sessionId = $db->real_escape_string($sessionId);
    $db->query("DELETE FROM sessions WHERE sessionid='$sessionId'");
    return true;
}

// define 'gcSession()' function
function gcSession($maxlifetime) {
    global $db;
    $db->query("DELETE FROM sessions WHERE expiry < NOW()");
    return true;
}

?>

This is the session setting for login:

$this->set_session(array_merge($rs->fetch_assoc(), array('expires' => time() + (15 * 60))));

set by function:

private function set_session($a=false) {
    if (!empty($a)) {
        $_SESSION['exp_user'] = $a;
    }
}

How does my login system check to see if I'm already logged in?

public function check_status() {
    if (empty($_SESSION['exp_user']) || @$_SESSION['exp_user']['expires'] < time()) {
        return false;
    } else {
        return true;
    }
}

Turns out, the value of $_SESSION, according to var_dump is array(0) { }

and the check in the web application itself:

// This is in authorisation.php

if(empty($_SESSION['exp_user']) || @开发者_如何转开发$_SESSION['exp_user']['expires'] < time()) {
        header("location:/login.php");  //@ redirect 
} else {
    $_SESSION['exp_user']['expires'] = time()+(15*60);  //@ renew 15 minutes
        //echo $SID = session_id();
}

Now, this is what I have in that index.php file at the top:

require('includes/session.functions.php');
session_set_save_handler('openSession', 'closeSession', 'readSession', 'writeSession', 'destroySession', 'gcSession');
session_start();
include('includes/authorisation.php');

Here's the database:

If I comment out session_set_save_handler(), we don't get the loop, however, if I keep it there in action, I get the loop between index and the login system (already logged in -> index ::check login loop.)

print_r(session_set_save_handler('openSession', 'closeSession', 'readSession', 'writeSession', 'destroySession', 'gcSession')); == 1 

var_dump(session_set_save_handler('openSession', 'closeSession', 'readSession', 'writeSession', 'destroySession', 'gcSession')); == bool(true)

Any ideas what I'm doing wrong?

It seems you are mixing up two different time formats. In mysql, NOW() gives you a time in the format:

Returns the current date and time as a value in 'YYYY-MM-DD HH:MM:SS' or YYYYMMDDHHMMSS.uuuuuu format, depending on whether the function is used in a string or numeric context.

In php, time() gives you:

Returns the current time measured in the number of seconds since the Unix Epoch (January 1 1970 00:00:00 GMT).

In your sql statements you are comparing the two and you can´t as they are completely different formats.

It turns out that there was an extra session_start(), which would reset the session.