Create new session id

# session_create_id

(PHP 7 >= 7.1.0)

session_create_id — Create new session id

### 説明

session_create_id ([ string `$prefix` ] ) : string

session_create_id() is used to create new session id for the current session. It returns collision free session id.

If session is not active, collision check is omitted.

Session ID is created according to php.ini settings.

It is important to use the same user ID of your web server for GC task script. Otherwise, you may have permission problems especially with files save handler.

### パラメータ

`prefix`

  If `prefix` is specified, new session id is prefixed by `prefix`. Not all characters are allowed within the session id. Characters in the range a-z A-Z 0-9 , (comma) and - (minus) are allowed.

### 返り値

session_create_id() returns new collision free session id for the current session. If it is used without active session, it omits collision check.

### 例

例1 session_create_id() example with session_regenerate_id()

`<?php
// My session start function support timestamp management
function my_session_start() {
session_start();
// Do not allow to use too old session ID
if (!empty($_SESSION['deleted_time']) && $_SESSION['deleted_time'] < time() - 180) {
session_destroy();
session_start();
}
}
// My session regenerate id function
function my_session_regenerate_id() {
// Call session_create_id() while session is active to
// make sure collision free.
if (session_status() != PHP_SESSION_ACTIVE) {
session_start();
}
// WARNING: Never use confidential strings for prefix!
$newid = session_create_id('myprefix-');
// Set deleted timestamp. Session data must not be deleted immediately for reasons.
$_SESSION['deleted_time'] = time();
// Finish session
session_commit();
// Make sure to accept user defined session ID
// NOTE: You must enable use_strict_mode for normal operations.
ini_set('session.use_strict_mode', 0);
// Set new custome session ID
session_id($newid);
// Start with custome session ID
session_start();
}
// Make sure use_strict_mode is enabled.
// use_strict_mode is mandatory for security reasons.
ini_set('session.use_strict_mode', 1);
my_session_start();
// Session ID must be regenerated when
// - User logged in
// - User logged out
// - Certain period has passed
my_session_regenerate_id();
// Write useful codes
?>`

### 参考

- session_regenerate_id() - 現在のセッションIDを新しく生成したものと置き換える
- session_start() - 新しいセッションを開始、あるいは既存のセッションを再開する
- session.use_strict_mode
- SessionHandler::create_sid() - 新規セッション ID を返す