PHP session_start doesn't resume session

Question

I want to resume a session. So I'm passing session id and trying to resume session like so:

    session_save_path($_SERVER["DOCUMENT_ROOT"].'/mysessions');
    if(!empty($_POST['session_id'])) { 
      session_id($_POST['session_id']);  // $_POST['session_id'] = "4dkwkeiugraqhfpeq745l2c2a1";
      session_start();
    }

    $session_var = $_SESSION['property_name']; // <- null even though there was something there

    ob_start();
    var_dump($_SESSION);
    $session_data = ob_get_clean(); // $session_data = NULL

I see that physical session file exists ' sess_4dkwkeiugraqhfpeq745l2c2a1 ' in the session folder where I store my sessions. Three is data there. However, the session does not resume. After calling session_start() , $_SESSION variables are not there.

What am I misssing here?

Answer 1

What am I missing here?

That's hard to say. session_id() is the correct function to change the session id, however the session_save_path() might be a different one. So you think the session is on the disk, but it's the wrong directory.

Or even a different save handler, so not even saving to disk but into database.

Also inside your code I don't see any check to test if the $_SESSION is actually empty or not, so it's not clear where you check that. You should test this directly after session_start() so that you know if the data was loaded or not.