Educator

Cookies

• A cookie is a piece of information set by an HTTP server and sent to a web client within an HTTP response for storage by the client.
• Cookies are associated with a particular website, and each time a client requests a page from a website for which it has received & stored a cookie, it includes the corresponding cookie’s data within its HTTP request.
• HTTP is a stateless protocol meaning that each HTTP transaction between a client & server has no ‘memory’ of any previous transactions.
• The purpose of cookies is to allow state, or knowledge of previous events, to be introduced into HTTP transactions.
• The way a web server sends a cookie to a client is via the Set-Cookie header of an HTTP response:

  HTTP/1.1 200 OK
  Date: Wed, 3 Aug 2011 23:59:59 GMT
  Content-Type: text/html
  Set-Cookie: cookie=cookieValue
  Host: www.educator.com

• Cookie data is in the form of name-value pairs.
• Each time a client requests a page from a website for which it has a cookie, it sends the cookie’s information back to the server using the Cookie HTTP request header:

  GET /index.html HTTP/1.1
  Host: www.educator.com
  Cookie: cookie=cookieValue

• setcookie() is a built-in PHP function that allows a script to send a cookie to a web client. It must be called before any of a script’s output is generated.
• Cookies have several attributes that can be set which determine whether a client sends a particular cookie in its request for a page from a particular website:
  • domain – specifies the domain which a cookie applies to
  • path – specifies a particular path within a domain that the cookie applies to
  • expires – the data & time when a cookie is no longer valid
• $_COOKIE is a superglobal associative array containing any cookie name/value pairs sent by a client in its request for a PHP script.
• Additional Resources:
  • Reference - 'Unofficial' Cookie Specification
  • Function Reference - setcookie()
  • PHP Manual - $_COOKIE Superglobal