Session control in PHP

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Session Control

HTTP protocol is the mutual communication between WEB server and browser protocol, it is a stateless protocol, that is, each HTTP request is independent of each other. Therefore, the HTTP protocol does not have a built-in mechanism to maintain state between two transactions. For example, when a user requests one page and then requests another page, HTTP will not be able to tell us whether the two requests came from the same user.

In the website, we often need to track a variable: by tracking the variable, we can establish a connection between multiple request things, and then display different content and different pages based on authorization and user identity. This is session control technology.

Commonly used session control technologies include Cookie and Session. Simply put, Cookie determines the user's identity by recording information on the client side; Session determines the user's identity by recording information on the server side.

Cookie

Cookie is a small text file that is included in the HTTP request message and passed between the web server and the browser. The working principle of Cookie is as follows:

1. The server sets a Set-Cookie field in the HTTP response message and puts the Cookie data in the Set- The Cookie field is transmitted to the browser along with the HTTP message;

2. After receiving the HTTP response message, the browser checks Set-Cookie If the field has a value, a Cookie file will be created locally to save the data;

3. When the browser sends a request to the server again, the browser will first search for the locally saved Cookie file. If If there are any cookies related to the URL being connected in the Cookie file, set a Cookie field in the HTTP request message, add the data in the Cookie file to the field, and finally add the HTTP request message carrying the Cookie field. sent to the server.

Cookies can be used to save user names, passwords, personalized settings and other simple information. The following are instructions for using cookies:

Create

<?php
setcookie("Cookie", "cookievalue", time()+3600);

setcookie() must be called before the content of the HTML file is output

Receive

<?php
echo $_COOKIE["Cookie"];

Delete

<?php
#方法一：将值设为空
setcookie("Cookie", null);

#方法二：将过期时间设为过去时间
setcookie("Cookie", "value" , time());

Session

Session is to maintain the user on the server side A method of session data that works as follows:

1. When the browser accesses a PHP script for the first time, the seesion_start() function creates a unique Session ID (each client has a unique identification), and automatically saves this Session ID to the client cookie through the HTTP response header. At the same time, a file named with Session ID is also created on the server side to save the user's session information;

2. When the same user visits this website again, it will automatically pass HTTP The request header brings the Seesion ID saved in the Cookie;

3. The server PHP script receives the client request, and then the session_start() function will not Then assign a new Session ID, but search the server's hard disk for a Session file with the same name as the Session ID, and read out the session information previously saved for this user.

First of all, there are two ways to create a Session unique identifier: through Cookie or GET. By default, PHP will create a Cookie named PHPSESSID (the value of session.name can be modified through php.ini). If the client disables cookies, you can specify to pass the Session ID through GET. Go to the server (modify parameters such as session.use_trans_sid in php.ini). Secondly, Session is saved in the form of a file. There is a configuration item --session.save_path= "" in php.ini. The path filled in will save all Session files. The naming format of the Session file is: sess_[value of PHPSESSID]. Each file stores the data of a session. Finally, the data saved in the Session file is serialized, such as:

cityID|i:0;cityName|s:3:"all";fanwe_lang|s:5:"zh-cn";fanwe_currency|a:4:{s:2:"id";s:1:"1";s:6:"name_1";s:9:"人民币";s:4:"unit";s:3:"￥";s:5:"radio";s:6:"1.0000";}_fanwe_hash__|s:32:"77c18770c6cb5d89444c407aaa3e8477";

Session can also be used to save some simple information such as user name, password, personalized settings, etc. The following is the use of Session Description:

Create

//启动 session
session_start();

//注册session变量，赋值为一个用户的名称
$_SESSION["username"] = "jochen";

//注册session变量，赋值为一个用户的ID
$_SESSION["uid"] = 1;

Note: session_start() must be called before the content of the HTML file is output

Read

<?php
session_start();
echo $_SESSION["username"]; # # jochen
echo $_SESSION["uid"];      # 1

Destroy

<?php
session_start();
 
unset($_SESSION["username"]);
unset($_SESSION["uid"]);

It should be noted that when there are many session files, I/Q read and write performance problems will occur. At this time, caching systems such as memcached and redis can be used.

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