Question

I’ve binged a lot for this stuff, but couldn’t find direct ANSWER,
I’ve searched for this here,

But
I am still beating my head against the wall trying to implement,

How do I do update query after session expired?
I’m not talking about explicit clicking “Logout” button

Here’s basic SQL structure:

CREATE TABLE auth_users (

 email       varchar(40) NOT NULL,
 password    varchar(40) NOT NULL,
 online      ENUM('1') DEFAULT NULL  <-- HERE, it updates to 1 when user logged in, it updates back to NULL when user explicitly clicks on LOGOUT

) type=MyISAM;

Class Hierarchy:

interface {
    function login();
    function logout();
        //calls after succes authorization
        function set_as_online();
        //calls from within logout() method
        function set_as_offline();
}

BUT IT DOES NOT UPDATES BACK TO NULL WHEN USER CLOSES HIS BROWSER,

For example,
Assume we have two users: User-A, User-B

User A logged successfully, now User-B can see User-A as ONLINE user.

If User-A forget to click “LOGOUT” and would close his browser,
user-B still can see User-A as ONLINE. That’s the problem.

For example,
Facebook handles this very well,

Assume your friend just closed the browser (i.e his session does not exists anymore),
then somehow you can see him as OFFLINE

What am I doing wrong? Incorrect approach of handling offline/online users?

Answer 1

Another approach is needed here i think. Don’t set a online/offline flag, but a ‘last_seen’ timestamp. Ie. with every request update the record to the current timestamp. If you want to know if the user is online, just do:

if($current_time - $last_seen_time < $session_expire_limit) {
    // online
} else {
    // offline
}

Otherwise you’d need a cronjob of some sort to automatically reset the online flag in your database after a certain time, but then still you’d need a last_seen column.

// edit

i don’t know exactly how facebook does it, but it could be one of the following; for the chat and notify functionality facebook opens up a ‘stream’, which is in fact a little ajax call which is kept alive by the server (btw, this ajax call is refreshed every 40 seconds). Possibly this stream is used to track online users. Another option, but less likely, is that an event is attached to the window.unload event. This is less likely because a page refresh, a clicked link to another facebook page etc. is also triggering the event. This would mean that every time an internal facebook link is clicked the event should be unbinded from the browser.
Can’t think of another way atm, just some suggestions. Unfortunately those are quite labor-heavy to implement, I assume my suggestion above (before the edit) should be suitable for a common website.