CGI Programming with Perl

Cookies

• A Web server session is the collection of all requests made by a particular browser from start up of browser until user exists the browser
  
  The HTTP protocol is essentially stateless
  
  It has no means to store information about a particular of a particular browser to a specific Web server
  
  There are some very good reasons why it is useful for the server to be capable of connecting a request made during a session to other requests made by the same client during that session



• Cookies - general approach to storing information about a browser user on the browser system itself
  
  The server is given this information when the browser makes subsequent requests for Web resources from server
  
  Allows the server to present an interface that is customized for that client
  
  A cookie is an object sent by the sever to a connected browser to be stored
  
  Every HTTP communication includes a header which can include cookies
  
  When created, cookies are assigned a lifetime Created on the server and sent to the browser along with requested resource
  
  Browser returns its stored cookies every time it sends a subsequent request to that server, until lifetime ends
  
  Only the server that created the cookie can ever receive the cookie from the browser



• The CGI.pm includes a cookie function
  
  Serves to both create and retrieve existing cookies from the HTTP header of a request
  
  

  cookie( -name => a_cookie_name,
  -value => a_value,
  -expires => a_time_value );
  

  
  
  
  • The cookie name can be any string
  
  
  
  • The cookie value can be any scalar value
    
    References to arrays and hashes allow multiple cookies on one call
  
  
  
  • The expires value can be in many different units:
    
    
    • +4d specifies four days from now
    
    
    
    • s for seconds,
    
    
    
    • m for minutes,
    
    
    
    • h for hours,
    
    
    
    • M for months,
    
    
    
    • y for years
    
    
    
    • now for right now
    
    
    
    • A negative value of expires kills the cookie



• Cookies are placed in the HTTP header at the time of creation
  
  
  • With CGI.pm it is done when the header function is created.
    
    Pass the cookie as a parameter to header
    
    

    header(-cookie => $my_cookie);
    

• To retrieve the value of a cookie, the cookie function is called with the name of the cookie
  
  

  $lov = cookie('lov'); # gets value of cookie named lov
  




• When the cookie function is called without any parameters
  
  It returns a hash of all the cookies in the HTTP header of the current request
  
  

  print "Cookie Name \t Cookie value <br />"
  foreach $name (keys cookie() {
       print "$name \t cookie($name) <br />
  




• the Perl function localtime returns the current time and date corrected for the local time zone
  
  

  ($s, $mi, $h, $md, $mo, $y, $wd, $yd, $dst) = localtime;
  

  For days of the week
  
  

  $day_of_week = (qw(Sunday Monday Tuesday Wednesday Thursday Friday
                     Saturday Sunday))[(localtime[6]];
  




• The CGI program day_cookie.pl will do the following:
  
  
  1. Get the cookie named 'last_time'
  
  
  
  2. Get the current day of week, day of month, and put them in cookie named 'last_time'
  
  
  
  3. Put the cookie in the header of the return document
  
  
  
  4. If there was no existing cookie produce a welcome message for the first time visitor
  
  
  
  5. If there was a cookie, produce a welcome message that includes the previous day of the week, and day of the month