session_set_save_handler - Why isn't this code working?

Question

I've been trying to save PHP session data in a MySQL database, but can't get it to work.

For a simple example, here's code that should increment a counter with each visit. I've seen other examples, etc. but can someone please tell me why this code isn't working? (Apache/2.2.11 (Win32) DAV/2 mod_ssl/2.2.11 OpenSSL/0.9.8i PHP/5.2.9 MySQL client version: 5.0.51a)

Here is the mysql database table:

CREATE TABLE IF NOT EXISTS `sessions` (
  `session_ID` varchar(32) COLLATE utf8_unicode_ci NOT NULL,
  `session_data` mediumblob NOT NULL,
  `access` int(10) unsigned NOT NULL,
  PRIMARY KEY (`session_ID`),
  KEY `access` (`access`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

And the PHP code (just plug in your db credentials):

<?PHP

function mysession_open()
{

    global $sdbc;   // Session Database Connection

    if ($sdbc) {
        return true;
    } else {
        return false;
    }

}

function mysession_close()
{

    global $sdbc;

    return mysqli_close($sdbc);

}

function mysession_read($session_id)
{
    global $sdbc;

    $session_id = mysqli_real_escape_string($sdbc, $session_id);

    $sql_sel    = "SELECT session_data FROM sessions WHERE session_id = '$session_id'";
    $data_sel   = mysqli_query($sdbc, $sql_sel);
    $row_sel     = mysqli_fetch_array($data_sel);

    if (isset($row_sel['session_data'])) {
        return $row_sel['session_data'];
    } else {
        return '';
    }

}

function mysession_write($session_id, $session_data)
{
    global $sdbc;

    $access = time();

    $session_id    = mysqli_real_escape_string($sdbc, $session_id);
    $access        = mysqli_real_escape_string($sdbc, $access);
    $session_data   = mysqli_real_escape_string($sdbc, $session_data);

    $sql_write  =   "REPLACE INTO sessions (session_ID, session_data, access) " .
                    "VALUES ('$session_id', '$session_data', '$access')";

    return mysqli_query($sdbc, $sql_write);

}

function mysession_destroy($session_id)
{
    global $sdbc;

    $session_id = mysqli_real_escape_string($sdbc, $session_id);

    return mysqli_query($sdbc, $sql_del);
}


function mysession_gc($max)
{
    global $sdbc;

    $old = time() - $max;
    $old = mysqli_real_escape_string($sdbc, $old);

    $sql_old = "DELETE FROM sessions WHERE access < '$old'";

    return mysqli_query($sdbc, $sql_old);

}

global $sdbc;
$sdbc = mysqli_connect('localhost', '...', '...', '...') or die('Could not connect to SDBC');

session_set_save_handler('mysession_open','mysession_close','mysession_read','mysession_write','mysession_destroy','mysession_gc');
session_start();

if (isset($_SESSION['counter'])) {
    echo "counter is already set and it is " . $_SESSION['counter'] . '<br />';
    $_SESSION['counter']++;
} else {
    echo "counter is not set.  setting to 1<br />";
    $_SESSION['counter'] = 1;
}

echo "<br />Dumping SESSION data:<br />";
var_dump($_SESSION);

session_write_close();

?>

Thanks in advance for your help.

If you comment out the session_set_save_handler line of code, it works fine (it increments). But using the save handler it does not.

Answer 1

None of your query calls have any error checking. Instead of blindly assuming the database portion works, do some basic error checking at each stage, e.g:

function mysession_write($session_id, $session_data) {
    global $sdbc;

    [...snip...]

    $stmt = mysqli_query($sdbc, $sql_write);
    if ($stmt === FALSE) {
       error_log("Failed to write session $session_id: " . mysqli_error($sdbc);
    }
    return($stmt);
}

There's only way way for a query to succeed, but zillions of ways to fail.