Educator

Introduction to Sessions

• On the web, a session refers to a series of related communications between a web client & web server over a specific period of time that are used to:
  • Link multiple HTTP transactions
  • Preserve data over multiple transactions
• Data, or state, preserved between a series of related HTTP transactions is referred to as session data.
• A client-side session is when session data is stored by the web client, typically using cookies.
• A server-side session is when session data is stored by the web server, typically in a file, database, or in RAM.
• A unique session ID, or SID, is generated by a web server for each new server-side session.
• The SID is used by the server to:
  • Identify multiple HTTP transactions as being part of the same session
  • To access any data stored for the session
• A client passes an SID to the server with each HTTP request via either:
  • Cookies
  • URL Parameter
• PHP typically uses a cookie, known as a session cookie, to pass the SID of a session between the client & server with each HTTP request.
• PHP stores session data in flat files in the directory specified by the session.save_path configuration directive.
• session_start() either creates a new session or continues an existing session. If using cookie-based sessions, it must be called before any output is generated.
• $_SESSION is a superglobal used to store all session data and can be used to store data of any type, including arrays and objects.
• When a key/value pair is added to $_SESSION, the key's name is referred to as a session variable.
• To set, get, or delete session variables, standard associative array square bracket syntax & the unset() construct are used on the $_SESSION superglobal.
• There are a number of configuration directives related to sessions in 'php.ini':
  • session.cookie_lifetime – sets the expiration of a session cookie
  • session.cookie_domain – sets the domain a session cookie is valid for
  • session.cookie_path – sets the path a session cookie is valid for
  • session.use_cookies – sets that cookies should be used to transfer SIDs
  • session.use_trans_sid – sets that URL parameters should be used to transfer SIDs
  • session.use_only_cookies – can be used to enforce the use of cookies for transferring SIDs
• Additional Resources:
  • Function Reference - session_start()
  • PHP Manual - $_SESSION Superglobal
  • PHP Manual - Session Configuration Directives