CIS 451: Cookies

1
CIS 451 Cookies

• Dr. Ralph D. Westfall
• January, 2001

2
Problem

• server primarily tracks requests for files
• efficient for high volume of users
• usually doesn't know who is asking for files
• even if from link on file in same application
• need to send identification with request
• identification needs to associated with all files
  requested by same user of application
• can go in HTML form "hidden fields"

3
Possible Solutions

• password login
• advantage highest security
• disadvantage extra work for customer
• automated identification
• could generate a random to ID customer
• advantage no extra work for customer
• disadvantage only good for one session
• can' track repeat visits by same person

4
Another Solution Cookies

• information stored in file on client computer
• advantages
• user only needs to enter data one time
• data "persists," so it is available in later
  sessions
• disadvantages
• some users won't allow cookies
• cookies can be removed from user's computer
• replaced by newer ones, or manually cleared

5
Cookies

• cookies have names
• a cookie can have multiple values
• cookie data is accessed by the cookie name, and
  the keys if more than one value
• cookies are part of both the Request and Response
  ASP intrinsic objects
• created by Response.Cookies methods
• stored in Request.Cookies "collection"

6
Working with Cookies

• (need to control buffer if any output will be
  written prior to create/delete cookies)
• lt Response.Buffer true gt 'at top of file
• creating
• Response.Cookies("cookie")("key") "value"
• 'substitute "literals" or string variables for
• 'items within " "
• deleting
• Response.Cookies("cookie").Expires Date - 1000
• 'deletes on client, still in current session

7
Working with Cookies - 2

• accessing
• strValue Request.Cookies("cookie")("key")
• 'note that data is accessed from Request object
• testing to see if multiple values of cookie data
  are available
• blnValue Request.Cookies("cookie").HasKeys
• 'blnValue true if number of values gt 1

8
Cookie Exercise

• download cookiedata.asp and cookietest.asp from
  Code Samples
• add some more input fields to cookiedata.asp and
  modify cookietest.asp to output these new fields