Cookies allow your applications to store a small amount of textual data (typically,
4-6kB) on a Web client. There are a number of possible uses for cookies, although
their most common one is maintaining session state.Cookies are typically set by the server using a response header, and subsequently made available by the client as a request header.
this is from zce study guide.
My questions are
1. how a session state is maintained by cookie?
2. what happens to these cookies when we use session_destroy()?
Put simply, the session cookie ties a remote session to your browser as you navigate a given site. It contains a string usually along the lines of PHPSESSID=3432DFGDFG43523 which the remote server identifies as a session that it is managing.
From the PHP website:
A visitor accessing your web site is assigned a unique id, the
so-called session id. This is either stored in a cookie on the user
side or is propagated in the URL.
The session support allows you to store data between requests in the
$_SESSION superglobal array. 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() or implicitly through
session_register()) whether a specific session id has been sent with
the request. If this is the case, the prior saved environment is
recreated.
http://www.php.net/manual/en/intro.session.php
When session_destroy() is called, it doesn't quite behave as you'd expect. The session is destroyed remotely but the local cookie isn't removed. To do this you'd need to call setcookie(<session cookie name>) with a negative date to destroy it on the client side. Again, from the PHP website:
session_destroy() destroys all of the data associated with the current
session. It does not unset any of the global variables associated with
the session, or unset the session cookie. To use the session variables
again, session_start() has to be called.
In order to kill the session altogether, like to log the user out, the
session id must also be unset. If a cookie is used to propagate the
session id (default behavior), then the session cookie must be
deleted. setcookie() may be used for that.
http://www.php.net/manual/en/function.session-destroy.php
Very short:
A session id is created which is sent over to the client on each request, this is stored in a cookie usually called PHPSESSID. The client responds with this session id to tell the server which session it belongs to.
session_destroy only unsets the data, not the identity. So cookies are not touched using that method.
Related
After logging in a PHP web application and then clear the cookie in inspect element, will the session destroy?? If so,why?
By default php will use a cookie to track a user across page views.
When the page is requested, the session cookie is included, the server matches the session cookie value to a session and then makes the session information available in php when generating a response.
If you delete the cookie in web inspector / console, it can no longer be included with the request and the session will not be matched.
The session still exists on the server until the garbage collection process removes it, but without that cookie, it will never me matched.
In Internet Explorer, for example, you can enable first party cookies, third party cookies and allow session cookies.
I know the difference between:
a first party cookie and a third party cookie, and
a PHP session and a cookie.
But what is a session cookie? And how can you set one using PHP?
For example, you cannot log into Facebook without cookies enabled. However, if you allow session cookies, you can log into Facebook.
So, how does a session cookie differ from other kinds of cookies?
A cookie has a lifetime, after which it will expire (As denoted by the Expires directive). If you don't set a timeout, the browser will expire the cookie when you close the browser. This is called a session cookie.
These kind of cookies are often used to track a users current session state on the server side (E.g. php's sessions), but there is not a strong relation between the two uses of the word "session"
A session cookie holds the unique identifier that PHP generates when session_start() is called, so that each client can be associated with a session, and no two sessions can have the same ID at the same time.
The session cookie is usually destroyed when the browser window is closed, or can be done manually using session_destroy().
From Wikipedia:
Older definition: (2011-12-17)
A session cookie is created when no Expires directive is provided when
the cookie is created.
Latest definition:
A session cookie, also known as an in-memory cookie or transient
cookie, exists only in temporary memory while the user navigates the
website.[18] Web browsers normally delete session cookies when the
user closes the browser.[19] Unlike other cookies, session cookies do
not have an expiration date assigned to them, which is how the browser
knows to treat them as session cookies.
In PHP, when you use session_start() it creates a session, this will create a session cookie in the client browser, PHP needs the client to send this info back with each request so that PHP can tell the session ID.
We can send some cookies to visitor's browser by setcookie(). When defining a value with $_SESSION['value'], if using session.use_only_cookies, the session will be only stored on the visitor's browsers. What is the difference of these two cases?
EDIT: Obviously, they are basically different. I just meant the difference in their application. We can set a value on the client-side, which can be retrieved any time (before expiration of course) with $_COOKIE or $_SESSION equally; e.g. to identify a returning visitor.
A cookie is stored on the client-side(i.e. "within" the client/browser).
_SESSION is serialized and then stored on the server. This data is associated with a session id. E.g. when using the default filesystem session handler the filename reflects the session id. The client (or your script) has to provide that session id in subsequent requests so that php's session management can/will load the session data again. One mechanis for this is to use cookies. session.use_only_cookies=On lets php's session mechanism look only for session ids in cookies.
No, when you set session.use_only_cookies, the data from the session are not stored client-side. This settings only affects the way the session ID is transmitted between the client and the server.
Basically there are 2 ways of transmitting this session ID :
Cookie based
URL based (with a GET variable like PHPSESSID=...)
When using the setting session.use_only_cookies, it prevents the use of the URL to transmit the session ID, only the cookie can be used.
These are completely different things:
setcookie() sets a cookie in the browser, but this normally isn't the session cookie. The session cookie you create with session_start().
$_SESSION[] sets/gets a value to/from the session on server side.
session.use_only_cookies will make sure, that the session id is sent only with a cookie, and not for example in the url.
Hi I would like to know the difference between a php session and a cookie
The main difference being that session data is stored on the server, while cookie data is stored on the client. Therefore, a client can easily modify the cookie contents, but will have to work way harder to modify the session contents.
Cookies are a means to store information in the end-user's browser, so that the server can track the end-user.
Sessions are also implemented by using cookies, but the actual data is not in the browser; rather, it is stored in the user's session record on the server. In the case of sessions, cookies are used to identify a particular end-user's session identifier on the server records. Hence, they are a more secure way of storing user information.
A cookie is a ~piece of data stored on the client side.
Data stored in session is stored on the server side, and the various sessions are identified by cookies.
There are session and Cookies, both are used to store values or data. But there are some key differences between session and cookie: a cookie stores the data in your browser and a session is stored on the server. Cookie data is available in your browser up to expiration date and session data available for the browser run, after closing the browser we will lose the session information.
A cookie is often used to identify a user. A cookie is a small file that the server embeds on the user's computer. Each time the same computer requests a page with a browser, it will send the cookie too.
A session variable is used to store information about, or change settings for a user session. Session variables hold information about one single user, and are available to all pages in one application.
A cookie is an unique information that the user sends to the web server with each request in order to identify him. This unique id could be used to store information about this specific user on the server (session).
Cookies will only expire on expiry time or if you explicitly clean cookie / cache of your browser. Cookies will retain into the system even after you open your browser next day.
Cookies are stored on client's system so they are less secure.
Session will expire on its expiry time or if the browser has been closed. As session is stored on server so it is more secure.
So for a login module, a combination of session and cookie should be used
Cookies stored client side but session stored server side.
cookies is without sign out of the your email account and close it. once again can not enter username and password but your email account is open.
session is close the webpage once again open to starting page appier
best example to illustrate the difference bet. Session and Cookies is:-
when you Login as a member in any Site it Creates Sessions until you log out...
that is Session..
and Cookies when you browse websites the are stored on your computer's Main Memory that is Cookies
i-e Session is Server side
and cookies is Client side
We got three differences in general. The key difference would be cookies are stored in client side and sessions are stored in server side. The second difference would be cookies can only store strings. We can store our objects in sessions. Storing objects in sessions were really useful according to my experience. Another difference was that we could be save cookie for future reference, but session couldn’t. When users close their browser, they also lost the session.
PHP Sessions
PHP has built-in functions to save session variables. The variables are stored in state files. These state files need not be explicitly created and managed. The following are the steps for saving and retrieving values of session variables.
The setcookie() command must be issued before any printed output occurs because the cookie must be written as part of the HTTP header. PHP automatically parses any HTTP_COOKIE string into an associative array $_COOKIE. The value of the cookie can be retrieved from the cookie thus:
$_COOKIE["some_var"]
Cookie: A key/value pair that is stored by the user's browser and is available in the superglobal $_COOKIE array available in PHP. The cookie request is initiated with an explicitly defined expiration date. For example:
setcookie('cookieName', $some_value, time()+3600, "/", ".example.com")
On the next server request, $_COOKIE['cookieName'] will be available. If you use a browser tool to look at the cookie, it will have an expiration date.
Session Cookie: Identical to the above but defined without an expiration date. If you use the same browser tool it will say that the cookie expires at the end of the session; which is ultimately when you close your browser. For example:
setcookie('cookieName', $some_value);
PHP Session: a server side mechanism that will associate a bunch of data with a session id. Every time a session is invoked, it serializes/unserializes it. This could be more data than just a single key/value pair that a cookie supports, but the way of associating this data with a user is by creating a cookie (regular or session as described above) in their browser that contains the session id. This way, the right data can be retrieved for a given user based on the value of that cookie.
Both are super global, i.e, they can be used anywhere in the site.
Differences between sessions and cookies:
Cookies are stored in the browser (client side) while sessions are stored in the server (host).
Cookies are remembered till they are deleted while sessions are deleted when the user closes the tab/browser (depending on the browser).
Cookies can be seen by the user while sessions cannot.
Due to the reasons above, I would recommend to not store sensitive data in cookies and store the data that is to be remembered even after the user has left in cookies.
Cookie - Stored data in browser and will work on browser related and client side only...For example if you are trying to log in gmail account with username and password,After entered login successful if you close the current tab and after sometime opening same page the login page won't come it will open directly with login details..This is cookie..
Session - Stored data in server side for example same as cookie example after entered login details you will get notification as successful once you close the browser then open after some time it will ask again login details(more example shopping also)
I have never wanted to allow a user to stay logged in for any length of time so I never saw a use for a "remember me" feature. I started thinking about how it's done though and would like some clarification.
I'm currently storing my sessions in a database. What has always perplexed me was how, even though I do not explicitly set a cookie, one is placed in my browser. I'm a little confused because a session is a session and a cookie is a cookie. I don't see how a session sets a cookie.
I'd also like to know if, simply setting another session variable in the session array to keep the user logged in, would be sufficient or would I still need to set a cookie?
In order to pull the session data back from your database a key is needed. This is called the Session ID.
The session ID needs to be stored somewhere. Either as part of the URL string that the client posts back or, more commonly, in a cookie on the client. When the request is posted, session reads the value from the cookie and knows which record to pull back from session storage.
This happens automatically.
The only reason to use session is if the data you want to keep is greater than 4KB (browser limitations); or if the time required to pull the data from your server is greater than reading it from session storage.
If the amount of data you are storing is less than 4KB I would highly recommend you just set that in the cookie to begin with. I generally store things like the user id, user first name, and a couple other attributes. Bear in mind that it is trivial to inspect a cookies value, so this information should be encrypted prior to going to the client.
Another thing is if the query time to pull the data you need from the original source is small, then elect to do that instead of placing it in session. That way you only get it when you actually need it instead of with every single page load.
What has always perplexed me was how, even though I do not explicitly set a cookie, one is placed in my browser.
A session handler has to identify which session belongs to which user.
The vast majority of session libraries do this by setting a cookie.
(Is) setting another session variable in the session array to keep the user logged in would be sufficient or would I still need to set a cookie?
Most session libraries set session cookies. These are cookies without a specified expiry time. They expire when the browser closes and are not sufficient to implement a "Remember Me" feature (which is expected to persist across browser restarts, so must have an explicit expiry time).
Explaining the relationship between Cookie and Session:
PHP uses Cookie to uniquely identify the session for each user. That's the only more reliable way because cookie is sent each time you request a file from the server. Using the token in the cookie, which is also the Session identifier, PHP will look up the tmp directory to see if the session exists. If the session exists, the variables are loaded from the correct file and you will be able to access the variables on that session.
Therefore, cookies store the session identifier which is required to identify which user uses which session. This is also how Session Hijacking come about, when people can change the session identifying cookie to use another person's session identifier.
The underlying PHP session implementation sets the cookie. You can alter this and have the session ID value passed in the query string, but I don't recommend it. You don't use the cookie, PHP does. It references the session ID value stored in the cookie to perform lookups to session data.
I'd also like to know, if simply setting another session variable in the session array to keep the user logged in would be sufficient or would I still need to set a cookie?
As soon as the user closes the browser, the session is killed and the cookie is deleted. I don't believe any mechanism exits to persist the session value, and for good reason.