Chapter 35. Cookies

PHP transparently supports HTTP cookies. Cookies are a mechanism for storing data in the remote browser and thus tracking or identifying return users. You can set cookies using the setcookie() or setrawcookie() function. Cookies are part of the HTTP header, so setcookie() must be called before any output is sent to the browser. This is the same limitation that header() has. You can use the output buffering functions to delay the script output until you have decided whether or not to set any cookies or send any headers.

Any cookies sent to you from the client will automatically be turned into a PHP variable just like GET and POST method data, depending on the register_globals and variables_order configuration variables. If you wish to assign multiple values to a single cookie, just add [] to the cookie name.

In PHP 4.1.0 and later, the $_COOKIE auto-global array will always be set with any cookies sent from the client. $HTTP_COOKIE_VARS is also set in earlier versions of PHP when the track_vars configuration variable is set. (This setting is always on since PHP 4.0.3.)

For more details, including notes on browser bugs, see the setcookie() and setrawcookie() function.

User Contributed Notes
Cookies

mega-squall at caramail dot com
23-Feb-2005 04:04


I found a solution for protecting session ID without tying them to client's IP. Each session ID gives access for only ONE querry. On the next querry, another session ID is generated and stored. If somebody hacks the cookie (or the session ID), the first one of the user and the pirate that will use the cookie will get the second disconnected, because the session ID has been used.



If the user gets disconnected, he will reconnect : as my policy is not to have more than one session ID for each user (sessions entries have a UNIQUE key on the collomn in which is stored user login), every entries for that user gets wiped, a new session ID is generated and stored on users dirve : the pirate gets disconnected. This lets the pirate usually just a few seconds to act. The slower visitors are browsing, the longer is the time pirates get for hacking. Also, if users forget to explicitly end their sessions .... some of my users set timeout longer than 20 minutes !



IMPORTANT NOTE : This disables the ability of using the back button if you send the session ID via POST or GET.

James Olsen
21-Jan-2005 11:14


Tying the session to the IP of the user is not a good idea. Some users, notably AOL users, are behind a rotating proxy which means their hits to the server will actually be coming from different IP addresses over the duration of their visit. Trying the session to the IP will not work properly for those users.

myfirstname at braincell dot cx
24-Sep-2003 11:47


[Editor's note: Wilson's comment has been deleted since it didn't contain much useful information, but this note is preserved although its reference is lost]





Just a general comment on Wilton's code snippet: It's generally considered very bad practice to store usernames and/or passwords in cookies, whether or not they're obsfucated.  Many spyware programs make a point of stealing cookie contents.





A much better solution would be to either use the PHP built in session handler or create something similar using your own cookie-based session ID.  This session ID could be tied to the source IP address or can be timed out as required but since the ID can be expired separately from the authentication criteria the authentication itself is not compromised.





Stuart Livings