Check whether a session is new in PHP

Question

I have a website that needs to perform a certain backend function once per user session. I therefore want to be able to determine whether any given page view is the first within a given session.

According to the PHP docs:

session_start() creates a session or resumes the current one based on a session identifier passed via a GET or POST request, or passed via a cookie.

So is there any way to know whether the session is being created or resumed?

Or is this a situation where I have to check the current session ID against a list I maintain on the server, to check if it's been registered before? If so, does this necessitate writing to a database, or is there a less cumbersome, in-memory way of doing this?

score 8 · Accepted Answer · answered Jan 18 '12 at 01:23

8

<?php
session_start();
if(empty($_SESSION['exists'])){
    //handle completely new session here
}
$_SESSION['exists'] = true;
.... //continue on with normal request

answered Jan 18 '12 at 01:23

Kenaniah

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You should use `!isset()` instead of `empty()`. If the key does not exist, PHP is going to throw a Notice error with `empty()`. – animuson Jan 18 '12 at 01:29
Animuson - PHP doesn't throw notices for empties when the key doesn't exist in 5.3. Probably true of earlier versions as well. – Kenaniah Jan 18 '12 at 01:31

score 5 · Answer 2 · answered Jan 18 '12 at 01:24

5

All documented ways of checking for session "newness" have failed me in the past, so I tend to do

$_SESSION['existing']=true;

when starting a session, and then just testing

if (isset($_SESSION['existing'])) ...

answered Jan 18 '12 at 01:24

Eugen Rieck

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Thanks- confirms what Kenaniah said – Yarin Jan 18 '12 at 01:36

score 3 · Answer 3 · answered Jan 18 '12 at 01:23

3

Check if $_COOKIE['PHPSESSID'] is defined (or whatever the cookie name is if you changed it from default.

If the cookie doesn't exist, then the session has just been created.

answered Jan 18 '12 at 01:23

Niet the Dark Absol

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1

Which won't work if the session is propagated via another mechanism than cookies. – Eugen Rieck Jan 18 '12 at 01:24

Check whether a session is new in PHP

3 Answers3

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