Or in PHP in general. I need to check if a user is logged in when accessing a certain page. Tutorials recommend using sessions e.g
$sessionData = array('username'=>$username, 'status'=>1);
$this->session->set_userdata($sessionData);
And for better security they recommend using a db table.
What if I just store username and status in a database and then change status to 0 when people log out?
Whenever they need access to a certain page I just check if the status 1.
When you call session_start() PHP sets a cookie in the user's browser with a randomly-generated ID.
From then on in that file anytime you store a value in $_SESSION will [by default] be stored in a file in session.save_path at the end of the script. This file is identified by the session ID.
On subsequent requests the client sends their session ID cookie back to the server, so when you call session_start() in your script PHP can go and retrieve that session file and restore the contents to $_SESSION.
Literally anything you will write will simply be re-implementing this already-written behaviour, but without the added layers of security contributed over the years to the PHP project.
Related
When a visitor or a search bot is visiting my website.
Does PHP automatically create a session? if so. where is it stored and how can I see it, and what kind of information is stored about the session...
Thanks!
Sessions are not automatically created for visitors or bots. A session must be started using the
session_start() call (http://php.net/manual/en/session.examples.basic.php).
PHP sessions save session files at some path on the server by default, this path is specified by session.save_path. To set or get session variables, use PHP's $_SESSION superglobal. php.net has great examples of gettting started with using sessions.
This is answered in Sessions Introduction
When a visitor accesses your site, PHP will check automatically (if session.auto_start is set to 1) or on your request (explicitly through session_start()) whether a specific session id has been sent with the request. If this is the case, the prior saved environment is recreated.
Does it start a current session based on cookies? Got that from the PHP website. How does PHP control the session? If I start a session when a user opens up my login page, what do I even use that session for? Can I use the current session to get info about the logged in user?
The PHP session system lets you store securely data in the $_SESSION global array. A typical example is to store the user's identifier in the session when they type in their password:
if ($user = try_login($login, $password))
$_SESSION['user'] = $user;
Then, you can access that information on all other pages:
if (isset($_SESSION['user']))
// logged in !
echo user_name($_SESSION['user']);
The data is stored on the server, so there is no risk of tampering (on the other hand, mind your disk usage).
Starting the session lets the current request use $_SESSION. If this is the user's first visit, the array will be empty and a new session cookie will be sent for you.
Closing the session merely prevents the current request from using $_SESSION, but the data stays around for the next requests.
Destroying the session throws away all the data, forever. The sessions are destroyed a certain duration after the last visit (usually around 30 minutes).
I assume you want to know what a PHP session means for you, the programmer.
When you do session_start() you are telling PHP that you want to use the session. This is made available to you as an array called $_SESSION. You can use that like any other array with the difference that the stuff you put in there stays there from one page to another (provided you use session_start() at the beginning of each page).
The actual mechanism may vary depending on configuration (php.ini), but a typical installation can use cookies for the session. Let's assume that your webserver is on linux and you're using cookies. You do the following
session_start();
$_SESSION['name']='Bob';
When PHP sees this it creates a text file with a semi-random name (for example sess_a3tfkd5558kf5rlm44i538fj07), sticks the $_SESSION contents in there as plain text and then sends a cookie to the user with the session id, which can be used to find the session file (for example a3tfkd5558kf5rlm44i538fj07).
The next time the user comes back he hands in the session id in his cookie, PHP goes to the relevant file and loads its contents in $_SESSION.
You'll note that the actual information is kept on the server while the user is only given an id. Kinda like handing in your coat in a club and getting a ticket with a number on it.
PHP's session_start starts OR resumes an HTTP session, which is explained fairly well in this article:
http://en.wikipedia.org/wiki/Session_(computer_science)
The concept of an HTTP "session" isn't specific to PHP, it's used in many (all?) server side HTTP frameworks as one way to allow for some state to be stored/associated across different request/responses (since HTTP is stateless). A unique token (which is often, but not always, stored in a cookie) identifies a particular client, and the server can associate the "session."
Here's some more info about sessions and PHP in particular that may help: http://www.php.net/manual/en/book.session.php
Like it says in the Manual
session_start() creates a session or resumes the current one based on a session identifier passed via a GET or POST request, or passed via a cookie.
If you start a new session at your login page, the session is initially empty. You can store in it whatever you want, for instance, store the user id once the user has logged in. The session data is destroyed when you close the session.
You might want to read all chapters in the Session Extension Manual Pages and also see
what is session and cookies in php and where it stored
You can compare PHP session with the cookie, but session is the much more secure way of storing information. Cookie store data on user's computer, but session store on the server in a temporary file securely.
I have discussed session and how to use it on one of my blog post - How to start a PHP session, store and accessing Session data?
Below is an example code of storing data in PHP session:
<?php
session_start();
$_SESSION["name"] = "John";
?>
Below is the example of retriving the session data:
<?php
session_start();
echo $_SESSION["name"];
?>
The above code will display the name "John".
Source: How to start a PHP session, store and accessing Session data?
I need to store data in a session and make it available for other users.
I thought about to store that data in an Session, generate a random Link, which user 1 can send to user 2. The Session should expire after 3 Month.
The session name is the random code I generate which is simluar to the code I send with POST to receive it on the Secretlink with $_GET.
Is this working in general or am I on the wrong track?
Can I store a Session even when the user 1 left the website or will the session be terminated?
I also need to set the session via jQuery, but I couldn't find anything about expiration time of a session.
I already did it with a cookie, but of course that's not working with user 2.
Sessions are actually files, stored on the server. PHP sets a cookie with the session id, named PHPSESSID. You can also use the PHPSESSID GET parameter, but you would have to change that in the server's PHP settings. Using the GET parameter, you could pass that link to another visitor to let him use the session. You would also have to extend the session expiration time.
However, I wouldn't recommend sharing sessions with GET parameters. It could be a security risk when you are storing personal data in those sessions. I recommend that you write a small script that stores data in a database and that can be accessed (for reading and writing) by requesting an url or any url with a special GET or POST parameter.
One last thing, sessions are never accessible from jQuery directly. You would have to write a small script that requests data on your server via AJAX.
I am beginning to learn php. I have a question regarding sessions.
Right now, I know that session_start() creates a session variable.
What I don't know is, when I access the session I created, do I need to use session_start() again?
If yes...
Why is this? Because I already created a session and I wonder why it wouldn't last the entire browsing session.
because what i understand from it is, that it is going to create a new session.
No:
session_start() creates a session or resumes the current one based on a session identifier passed via a GET or POST request, or passed via a cookie.
http://php.net/session_start
Each new page you visit is an entirely new context for PHP. session_start allows you to reestablish a previous context/session/data.
The session_start function tells PHP to enable session tracking. It doesn't wipe out the session created by a previous page. You must call session_start() before you'll have access to any variables in $_SESSION.
Because of the manual session_start()
session_start — Start new or resume existing session
the same way you would connect to database every time you want to use it. it will connect to however you're storing your sessions. The session variables are no wiped out.
Also read more here but this should help to understand how sessions work:
When you are working with an application, you open it, do some changes
and then you close it. This is much like a Session. The computer knows
who you are. It knows when you start the application and when you end.
But on the internet there is one problem: the web server does not know
who you are and what you do because the HTTP address doesn't maintain
state.
A PHP session solves this problem by allowing you to store user
information on the server for later use (i.e. username, shopping
items, etc). However, session information is temporary and will be
deleted after the user has left the website. If you need a permanent
storage you may want to store the data in a database.
Sessions work by creating a unique id (UID) for each visitor and store
variables based on this UID. The UID is either stored in a cookie or
is propagated in the URL.
Session data is stored at the Server side but the reference or id to the session is stored on the client's browser cookie. For the server to know your session id we make a call to session_start() on each page it is required (at the top) so that the first thing done is to get the id from the user and retrieve the session data. It is required on every page whenever you want to access session data.
Here is a video tutorial also. http://blip.tv/step4wd/php-sessions_en-5983086
The answer is yes. You have to do that on every page. If you don't do that you get a undefined index error.
This will work because we include the file
Index.php
<?php
session_start();
//file doesn't have session_start
include "file.php";
?>
No: it is NOT always going to create a new session. It only tells the script that this page wants to start OR maintain an existing session.
A session is nothing more that a STATE AT THE SERVER that you carry from from page to page.
It is NOT accessible from the client (browser).
The only thing the browser must do to keep the session is passing an ID (called default PHPSESSID in PHP).
This ID can be stored in a cookie, GET or POST, as long as you get it transfered to the server with each request you make.
Youve to use session_start(), everywhere you need to work with session like, creating, accessing, destroying.
Unlike cookies, you can't access or work with session unless you initiate the session.
Does it start a current session based on cookies? Got that from the PHP website. How does PHP control the session? If I start a session when a user opens up my login page, what do I even use that session for? Can I use the current session to get info about the logged in user?
The PHP session system lets you store securely data in the $_SESSION global array. A typical example is to store the user's identifier in the session when they type in their password:
if ($user = try_login($login, $password))
$_SESSION['user'] = $user;
Then, you can access that information on all other pages:
if (isset($_SESSION['user']))
// logged in !
echo user_name($_SESSION['user']);
The data is stored on the server, so there is no risk of tampering (on the other hand, mind your disk usage).
Starting the session lets the current request use $_SESSION. If this is the user's first visit, the array will be empty and a new session cookie will be sent for you.
Closing the session merely prevents the current request from using $_SESSION, but the data stays around for the next requests.
Destroying the session throws away all the data, forever. The sessions are destroyed a certain duration after the last visit (usually around 30 minutes).
I assume you want to know what a PHP session means for you, the programmer.
When you do session_start() you are telling PHP that you want to use the session. This is made available to you as an array called $_SESSION. You can use that like any other array with the difference that the stuff you put in there stays there from one page to another (provided you use session_start() at the beginning of each page).
The actual mechanism may vary depending on configuration (php.ini), but a typical installation can use cookies for the session. Let's assume that your webserver is on linux and you're using cookies. You do the following
session_start();
$_SESSION['name']='Bob';
When PHP sees this it creates a text file with a semi-random name (for example sess_a3tfkd5558kf5rlm44i538fj07), sticks the $_SESSION contents in there as plain text and then sends a cookie to the user with the session id, which can be used to find the session file (for example a3tfkd5558kf5rlm44i538fj07).
The next time the user comes back he hands in the session id in his cookie, PHP goes to the relevant file and loads its contents in $_SESSION.
You'll note that the actual information is kept on the server while the user is only given an id. Kinda like handing in your coat in a club and getting a ticket with a number on it.
PHP's session_start starts OR resumes an HTTP session, which is explained fairly well in this article:
http://en.wikipedia.org/wiki/Session_(computer_science)
The concept of an HTTP "session" isn't specific to PHP, it's used in many (all?) server side HTTP frameworks as one way to allow for some state to be stored/associated across different request/responses (since HTTP is stateless). A unique token (which is often, but not always, stored in a cookie) identifies a particular client, and the server can associate the "session."
Here's some more info about sessions and PHP in particular that may help: http://www.php.net/manual/en/book.session.php
Like it says in the Manual
session_start() creates a session or resumes the current one based on a session identifier passed via a GET or POST request, or passed via a cookie.
If you start a new session at your login page, the session is initially empty. You can store in it whatever you want, for instance, store the user id once the user has logged in. The session data is destroyed when you close the session.
You might want to read all chapters in the Session Extension Manual Pages and also see
what is session and cookies in php and where it stored
You can compare PHP session with the cookie, but session is the much more secure way of storing information. Cookie store data on user's computer, but session store on the server in a temporary file securely.
I have discussed session and how to use it on one of my blog post - How to start a PHP session, store and accessing Session data?
Below is an example code of storing data in PHP session:
<?php
session_start();
$_SESSION["name"] = "John";
?>
Below is the example of retriving the session data:
<?php
session_start();
echo $_SESSION["name"];
?>
The above code will display the name "John".
Source: How to start a PHP session, store and accessing Session data?