Detailed explanation of how to use sessions in PHP Page 1/2

Since the Session is stored on the server side in the form of a text file, there is no fear of the client modifying the Session content. In fact, in the session file on the server side, PHP automatically modifies the permissions of the session file, retaining only system read and write permissions, and cannot be modified through ftp, so it is much safer. PHPChina Open Source Community Portal

For Cookie, if we want to verify whether the user is logged in, we must save the user name and password (possibly an md5 encrypted string) in the Cookie, and request the page every time to verify. If the username and password are stored in the database, a database query must be executed every time, causing unnecessary burden on the database. Because we can't do just one verification. Why? Because the information in the client cookie may be modified. If you store the $admin variable to indicate whether the user is logged in, when $admin is true, it means logged in, and when it is false, it means not logged in. After passing the verification for the first time, store $admin equal to true in the cookie, and there will be no need to verify next time. Okay, is this right? Wrong. If someone forges a $admin variable with a value of true, doesn't that mean he or she will immediately gain administrative rights? It's very unsafe.
The Session is different. The Session is stored on the server side. Remote users cannot modify the contents of the session file. Therefore, we can simply store a $admin variable to determine whether to log in. After the first verification is passed, set the $admin value to true. , and later determine whether the value is true. If not, go to the login interface, which can reduce a lot of database operations. And it can reduce the insecurity of passing the password every time to verify the cookie (session verification only needs to be passed once, if you do not use the SSL security protocol). Even if the password is md5 encrypted, it can be easily intercepted.
Of course, there are many advantages to using session, such as easy control and user-defined storage (stored in the database). I won’t say much more here.
Does the session need to be set in php.ini? Generally not required, because not everyone has the permission to modify PHP.ini. The default storage path of the session is the system temporary folder of the server. We can customize the storage In its own folder, which I will introduce later.
Start to introduce how to create a session. Very simple, really.
Start the session and create a $admin variable:

Copy the code The code is as follows:

 
　// Start session 
　session_start(); 
　 // Declare a variable named admin and assign a null value. 
 $_session["admin"] = null; 
?> 

If you use Seesion, or the PHP file wants to call the Session variable, then it must be To start a Session before calling it, use the session_start() function. You don’t need to set anything else, PHP automatically creates the session file.
After executing this program, we can find the session file in the system temporary folder. Generally, the file name is in the form: sess_4c83638b3b0dbf65583181c2f89168ec, followed by a 32-bit encoded random string. Open it with an editor and take a look at its content:
admin|N;
Generally, the content is structured like this:
Variable name | Type: length: value;
Separated by semicolons every variable. Some can be omitted, such as length and type.
Let’s take a look at the verification program, assuming that the database stores the username and md5 encrypted password:

Copy the code The code is as follows:

 
 // After the form is submitted... 
 $posts = $_POST; 
 // Clear some whitespace symbols 
 foreach ($posts as $key => $value) 
{ 
 $posts[$key] = trim($value); 
　} 
 $password = md5($posts["password"]); 
 $username = $posts["username"] ; 
　$query = "Select `username` FROM `user` Where `password` = '$password'"; 
　 // Get query results
 $userInfo = $DB->getRow($query ); 
 if (!empty($userInfo)) 
 session 
　session_start(); 
　//Register the admin variable for successful login and assign the value true 
　$_session["admin"] = true; 
　} 
　else 
　{ 
　die("Username and password are incorrect"); Start the session on the user verification page to determine whether to log in: 
 // Prevent global variables from causing security risks 
 $admin = false; 
 // Start the session, this step is essential 
 session_start(); 
 // Determine whether to log in 
 if (isset($_SESSION["admin"]) && $_session["admin"] === true) 
{ 
 echo "You have logged in successfully" ; 
　} 
　else 
　{ 
　 // Verification failed, set $_session["admin"] to false 
　$_session["admin"] = false; 
　die( "You do not have permission to access"); 
　} 
　?> 

 
 Isn’t it very simple? Just think of $_session as an array stored on the server side. We registered Each variable is a key to the array, no different from using an array. 
What should I do if I want to log out of the system? Just destroy the session. 



Copy code

 The code is as follows:

　session_start();
　// This method is to copy the originally registered certain Destroy variables
unset($_session["admin"]);

// This method is to destroy the entire session file session_destroy(); ?>

Can Session set the life cycle like Cookie? With Session, will Cookie be abandoned completely? I would say that it is most convenient to use session in combination with Cookie.

 How does the Session determine the client user? It is determined by the Session ID. What is the Session ID is the file name of the Session file. The Session ID is randomly generated, so it can ensure uniqueness and randomness. sex to ensure the security of the Session. Generally, if the Session life cycle is not set, the Session ID is stored in the memory. After closing the browser, the ID is automatically logged out. After re-requesting the page, a new session ID is registered. 
 If the client does not disable cookies, the cookie plays the role of storing the session ID and session lifetime when starting the session. 
 Let’s manually set the session lifetime: 

Copy code

The code is as follows:

session_start();
// Save for one day
$lifeTime = 24 * 3600;

setcookie(session_name(), session_id(), time() + $lifeTime, “/”); ?> In fact, Session also provides a function session_set_cookie_params(); to set the lifetime of Session. This function must be called before the session_start() function is called:

Copy code 

 The code is as follows:

// Save for one day
$lifeTime = 24 * 3600;
session_set_cookie_params($lifeTime);

session_start(); $_session["admin"] = true; 　?>

If the client uses IE 6.0, there will be some problems with the session_set_cookie_params(); function setting Cookie, so we still call setcookie manually function to create cookies.

What should I do if the client disables cookies? There is no way, the entire life cycle is the browser process. As long as you close the browser and request the page again, you have to re-register the Session. So how to pass the Session ID? Pass it through the URL or through a hidden form. PHP will automatically send the session ID to the URL. The URL is in the form: http://www.openphp.cn /index.php?PHPSESSID=bba5b2a240a77e5b44cfa01d49cf9669, where The parameter PHPSESSID in the URL is the Session ID. We can use $_GET to obtain the value, thereby transferring the session ID between pages.

Copy code

The code is as follows:

 
 // Save for one day 
 $lifeTime = 24 * 3600; 
 // Get the current session name, the default is PHPSESSID 
 $sessionName = session_name(); 
 // Get the session ID 
　$sessionID = $_GET[$sessionName]; 
　// Use session_id() to set the obtained session ID 
　session_id($sessionID); 
　session_set_cookie_params($lifeTime); 
　session_start (); 
　$_session["admin"] = true; 
　?> 

　For virtual hosts, if all users’ Sessions are saved in the system temporary folder , will cause maintenance difficulties and reduce security. We can manually set the save path of the Session file. session_save_path() provides such a function. We can point the session storage directory to a folder that cannot be accessed through the Web. Of course, the folder must have read-write attributes.

Copy code The code is as follows:

 
　 // Set up a storage directory 
 $savePath = “./session_save_dir/” ; 
 // Save for one day 
 $lifeTime = 24 * 3600; 
 session_save_path($savePath); 
 session_set_cookie_params($lifeTime); 
 session_start(); 
 $_session[" admin"] = true; 
　?> 

Like the session_set_cookie_params(); function, the session_save_path() function must also be called before the session_start() function is called.
We can also store arrays and objects in session. There is no difference between operating an array and operating a general variable. When saving an object, PHP will automatically serialize the object (also called serialization) and then save it in the session. The following example illustrates this:

Copy code The code is as follows:

 
　class person 
　{ 
　var $ age; 
 function output() { 
 echo $this->age; 
 } 
 function setAge($age) { 
 $this->age = $age; 
 >　} 
　} 
　?> 

　setage.PHP

Copy code The code is as follows:

 
 session_start(); 
 require_once “person.PHP”; 
 $person = new person(); 
 $person->setAge(21); 
 $_session[ 'person'] = $person; 
 echo "check here to output age"; 
 ?> 

output.PHP

Copy the code The code is as follows:

 
　 // Set the callback function to ensure that the object is rebuilt. 
 ini_set('unserialize_callback_func', 'mycallback'); 
 function mycallback($classname) { 
 $classname . “.PHP”; 
 } 
 session_start(); 
 $ person = $_session["person"]; 
　 // Output 21 
　 $person->output(); 
　?> 

When we execute setup.php file, the setage() method is called, the age is set to 21, and the status is serialized and saved in the session (PHP will automatically complete this conversion). When going to output.php, this value should be output , the object just saved must be deserialized, and because an undefined class needs to be instantiated during deserialization, we define a later callback function that automatically includes the person.PHP class file, so the object is reconstructed. And get the current age value as 21, and then call the output() method to output the value.

Detailed explanation of how to use sessions in PHP Page 1/2_PHP Tutorial