Achieve sharing a SESSION under multiple domain names

To realize multi-domain name sharing session, you must first understand the operating mechanism of SESSION. I won’t go into the basic concepts.
Session works like this:
User A visits site Y. If site Y executes session_start(); (the following assumes that session_start() always exists), then a session_id will be generated. This session id will generally be saved in the form of COOKIE. User A (We can force the SESSION ID to be passed in COOKIE by setting session.use_only_cookies to 1 in php.ini.). At this time, the SESSION ID appears as $_COOKIE['PHPSESSID']; (PHPSESSID can be modified by the session_name() function)
User A then visits, this session id ($_COOKIE['PHPSESSID']) will be used every time A visits Y when transmitted to site Y.
On site Y, there will be such a directory, which is used to save the actual data of SESSION. Site Y receives the session id, and then obtains the association with the SESSION data through the session id, and returns the SESSION data.

Maybe you are smart and have already thought of it, since the SESSION between the server and the client is connected through a SESSION ID, and the SESSION data is saved in a specific folder in the form of an ordinary file.
Then if we want to implement different domain names, we only need to meet the following two conditions:

1) The SESSION data directories of different domain names can be unified together or updated simultaneously.

2) For the same customer, use a unified SESSION ID

implementation of the first condition.
If it is the same server, there is no need to make any settings.
If it is clustered/distributed, then I don’t think there is any need for me to say anything. . Those who can do distributed applications should have more experience in directory sharing than me. I haven't tested too many servers, and there are reasons for both subjective and objective conditions.

I mainly want to talk about the second condition here - making different domain names have a unified SESSION ID.
Then how should we unify?
First, this SESSION ID must be passed between different domain names, and since the cookie must be specific to the domain name, the transfer action is completed by the client. If the delivery process is not completed by the client, then the domain name being delivered does not know which client it is for.

The second step is to modify the SESSION ID under the domain name that accepts the transfer.

How to deliver:
In HTML, we can use many methods. For example
iframe

or .js

or an img html Element

As long as a certain address can be called, it will be fine.

In wml, due to the characteristics of wml script, we cannot call it in the form of script, and there is no iframe in wml.. But we can still transfer it through img.

How to modify:
Since the SESSION ID is usually passed through COOKIE, then we only need to pass $_COOKIE['PHPSESSID'];. But if the PHPSESSID is changed by session_name, we have to modify the PHPSESSID in setcookie. This will become very troublesome. . So we can choose a session-specific function session_id to modify $_COOKIE['PHPSESSID'];

A few points to note:

If session.use_only_cookies is 0 (PHP default), then the session id may be url or Passing in other forms

session_id() and session_name must be used before session_start()

The following is a simple class I wrote to implement multiple domain names. If you don’t understand the above, you can take a look at my multi-domain name class. This class is implemented in iframe form under HTML.

/*

Use:
Server A, Server B, log in to A’s index.php, create a file in B to receive SESSION, such as ses_get.php
Make the following modifications to A’s index.php
Most Start adding session_start();

, anywhere write: mdSession::_set('B/ses_get.php')
and ses_get.php write mdSession at the beginning: :_get();
@Author: surfchen@gmail.com http://www.surfchen.org/ */
function mdSession()
{

} function set($urls)
{ if (!is_array($urls))
{ $urls=array($urls); } foreach ($urls as $value)
{ echo ' '; } return true; } function get()
{ session_id($_SERVER ['QUERY_STRING']); session_start(); return true; } function _set($urls)
{ $obj=new mdSession(); return $obj->set($urls); } function _get()
{ $obj=new mdSession(); return $obj->get(); }
}?>

index.php :

include "mdSession.php";

session_start();

$_SESSION['php']="yogurt8";

mdSession::_set('http://www.b.com/ses_get.php');

var_dump($_SESSION );

?>

ses_get.php

include "mdSession.php";

mdSession::_get();

?>

b.php :

session_start();

var_dump( $_SESSION );

First visit http://www.a.com/a.php and then go to http://www.b.com/b.php to see the effect

It doesn’t work in firefox and Google Chrome Problem, but it still doesn’t work under Ie