PHP session and cookie summary sharing

This article mainly shares with you a summary of PHP sessions and cookies, hoping to help everyone.

1. The relationship between cookie and session
Although the cookie and session solutions belong to the client and server respectively, the implementation of the server's session is dependent on the client's cookie; the steps are roughly as follows:
1. The server executes the Session mechanism
2. Generate the corresponding and unique session_id (by parsing and processing this session_id, the server can find the file saved by the session; and then extract the session information from the file )

3. The server will send this session_id to the client
The client receives the session_id and saves it with cookie as a storage container
4. The client will send the session_id to the client in each request This session_id will be brought to the server when
The server parses the session by itself

Note: There are many ways to save information in a session: cache, database, file, etc.; but the default is to save it in file form. . .

2. Timing of creating session and destroying session
When creating a session, a cookie will be created, and its MaxAge is -1, which means it can only exist in memory. When cookies are disabled on the browser, this cookie will still be created.
When the request submitted by the browser contains the jsessionid parameter or cookie header, the container no longer creates a new session, but only finds the previous session for association. There are two situations here:
1) Use jsessionid. If this value can correspond to an existing session, no new session will be created. Otherwise, a new session will still be created.
2) Use cookies. If this value can correspond to an existing session, no new session will be created; but if there is no session corresponding to it (like after restarting the server above) the container will restore the corresponding session based on the cookie information, as if It's been the same before.
3.When is the session destroyed?

When we close the browser, open it again, and connect to the server, the server will allocate a new session, which means a new session will be started. So has the original session been destroyed? I did a small experiment:

Create a session:

session_start();//Register the session variable and assign $_SESSION["username"] = "hello"//Output generation session_idecho session_id();

Visit the page to create a session, get the session_id, close the browser;

Create a session object based on session_id

$session_id = "qpk6onnn3husvotnke030ftcm4";
session_id($session_id);
session_start();
echo $_SESSION["username"];  //结果取出session

So

When the browser is closed, the original session is not destroyed (the destroy method is not executed), but the session is destroyed until the timeout expires. Closing the browser only clears the cookies related to the original session in the client's memory. When the browser is opened again to connect, the browser cannot send cookie information, so the server will think it is a new session. Therefore, if there are certain resources associated with the session that you want to clean up when you close the browser (such as temporary files, etc.), you should send a specific request to the server instead of waiting for the session to be automatically cleaned up.

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