PHP session_id () function in detail, the session ID generation process and Sessions ID length _php instance

PHP session_id () function prototype and description session_id () function Description: stringsession_id ([string$id]) session_id () can be used to get/set the current session ID. In order to be able to easily attach the session ID to the URL, you can use the constant SID to get the string lattice ...

SESSION_ID () function prototype and description in PHP

SESSION_ID () function Description:

String session_id ([string $id])

SESSION_ID () can be used to get/set the current session ID.

To be able to attach a session ID to a URL conveniently, you can use the constant SID to get the session name and ID expressed in string format. Please refer to session processing.

session_id () function parameter:

Id

If the value of the ID parameter is specified, the specified value is used as the session ID. The session_id () function must be called before the Session_Start () function is called. Different session managers have different restrictions on the characters that can be used in the session ID. For example, the file session Manager only allows the following characters to be used in the session ID: A-Z-z 0-9, (comma) and-(minus)

Note: If you send a session ID by using a cookie, and you specify an ID parameter, a new cookie is sent to the client after the call to Session_Start (), regardless of whether the current session ID and the newly specified session ID are the same.

session_id () function return value:

SESSION_ID () returns the current session ID. If there is currently no session, an empty string ("") is returned.

How the PHP session ID is generated and the session ID length

A visitor visiting your Web site will be assigned a unique ID, which is called the session ID. This ID can be stored in a cookie on the client side, or it can be passed through a URL. Session sessions are used to track each user's sessions and are identified using server-generated SessionID to differentiate users. The session is stored in the server's memory, and the SessionID is stored in the server memory and the client's cookie. Thus, when a user makes a request, the server SessionID the user's cookie and the SessionID in the server's memory to find the user's corresponding session. Therefore, the session is not available if the client prohibits cookies.

How is the PHP session ID generated? Introduction to PHP default session ID generation algorithm

Take the source code of php5.3.6 as an example, enter the/ext/session directory, the function of generating session ID is located in the 345 lines of session.c file, the C language function prototype is as follows:

Phpapi Char *php_session_create_id (Ps_create_sid_args);

Interested can be specific analysis of the implementation principle.

PHP Default session ID length

Intercept some of the actual PHP 5.4.6 server generated session ID as follows:

Sess_00nrqa20hjrlaiac0eu726i4q5 sess_89j9ifuqrbplk0rti2va2k1ha0 SESS_G2RV1KD6IJSJ6G6C9JQ5MQGLV5
Sess_04es72a83tqsl0jqd3cvrc4s01 sess_8b7a5lme60g49lvk4u4jiemdn1 Sess_g3uk6d3gbashg5eoq0b2k7vsk0
Sess_04u0ns0oobh2g93t009bij2rq0 SESS_8DFVKIV8ML44FDQRK1RCMJCHS4 Sess_g64tddhbo8pbj8bs7bel44rf35
Sess_0592dolr5m0k392fah6c9preg7 sess_8fhgkjuakhatbeg2fa14lo84q1 sess_g6kl828qqsnvdrse7ff52cl2a4
Sess_066g8irr0m22iqotscepub4e13 sess_8gn03i9j1tta7655qfj6nl1l53 Sess_g8t45j6qce7mf55nk14cotj5i4
sess_08nr1fav9jqs2pdi5qlpsmd247 Sess_8gvu05313o7p9usksaacaiegu6 sess_gbtjmr57iat86c8ve86ar5nh30

See the specific session ID is "Sess_" after the section, length 26 bits, this length is limited to PHP 5.4.6.

The PHP session_id () Usage code is as follows:

Output session_id () detail code:

<?php
  session_start ();
  Echo session_id ();
  Output 08nr1fav9jqs2pdi5qlpsmd247
?>

Set session_id () detail code:

<?php
  session_id ("www.169it.com");
  Session_Start ();
  Echo session_id ();
  Output www.169it.com
?>