Home > Articles > Programming > ASP .NET

  • Print
  • + Share This
This chapter is from the book

10.4 Cookie State

Although not part of the HTTP specification (yet), cookies are often used to store user preferences, session variables, or identity. The server issues a Set-Cookie header in its response to a client that contains the value it wants to store. The client is then expected to store the information associated with the URL or domain that issued the cookie. In subsequent requests to that URL or domain, the client should include the cookie information using the Cookie header. Some limitations of cookies include the fact that many browsers limit the amount of data sent through cookies (only 4,096 bytes are guaranteed) and that clients can potentially disable all cookie support in their browser.

ASP.NET provides an HttpCookie class for managing cookie data. Listing 10-16 shows the HttpCookie class definition and the cookie collection properties exposed by the request and response objects. Note that the request and response objects both expose the collection of cookies through the HttpCookieCollection type, which is just a type-safe derivative of the NameObjectCollectionBase class, designed for storing HttpCookie class instances. Each cookie can store multiple name/value pairs, as specified by RFC 2109, which are accessible through the Values collection of the HttpCookie class or indirectly through the default indexer provided by the class.

Listing 10-16: The HttpCookie Class

NotInheritable Public Class HttpCookie
  Public          Property Domain  As String
  Public          Property Expires As DateTime
  Public ReadOnly Property HasKeys As Boolean
  Public Default  Property Item( _
              ByVal key As String) As String
  Public          Property Name    As String
  Public          Property Path    As String
  Public          Property Secure  As String
  Public          Property Value   As String
  Public ReadOnly Property Values  As NameValueCollection
  '...
End Class

NotInheritable Public Class HttpRequest
  Public ReadOnly Property Cookies As HttpCookieCollection
  '...
End Class

NotInheritable Public Class HttpResponse 
  Public ReadOnly Property Cookies As HttpCookieCollection
  '...
End Class

To request that a client set a cookie, add a new HttpCookie instance to the response cookie collection before your page rendering. To access the cookies that the client is sending with any given request, access the Cookies collection property of the request object. Listing 10-17 shows an example of a page that sets and uses a cookie named "Age". If the cookie has not been set, the page adds the cookie to the Response.Cookies collection with a value from a field on the form (ageTextBox). If the cookie has been set, the current value is pulled from the Request.Cookies collection and is used instead.

Listing 10-17: Using Cookies in ASP.NET

Private Sub Page_Load(ByVal sender As Object, _
                      ByVal e As EventArgs)
  Dim age As Integer = 0
  If (Request.Cookies("Age") Is Nothing) Then
    ' "Age" cookie not set, set with this response
    Dim ac As HttpCookie = New HttpCookie("Age")
    ac.Value = ageTextBox.Text
    Response.Cookies.Add(ac)
    age = Convert.ToInt32(ageTextBox.Text)
  Else
    ' use existing cookie value...
    age = Convert.ToInt32(Request.Cookies("Age").Value)
  End If
  ' use age to customize page
End Sub

Although cookies are typically used to store user-specific configuration information and preferences, they can be used to store any client-specific state needed by an application (as long as that state is converted to string form). It is interesting to contrast our earlier shopping cart implementation using session state with an equivalent implementation using only cookies. The major change in our implementation is the population and retrieval of the shopping cart contents from cookies instead of directly from session state. This can be done by converting the contents of the shopping cart into string form so that it can be sent back as cookies to the client and later restored on subsequent requests. To facilitate this, we have added two new functions to our Item class: HydrateArrayListFromCookies and Save-ArrayListToCookies. The first function is called from within the Load event handler of our shopping Page class, and the second function is called from within the PreRender event handler. The implementation of these two functions is shown in Listing 10-18. The rest of our code remains the same because we have changed only how the ArrayList is persisted. Listing 10-19 shows the cookie-based implementation of our shopping cart application.

Listing 10-18: Item Class with Cookie Serialization Support

Public class Item
  Public Shared Function HydrateArrayListFromCookies() _
                         As ArrayList
    Dim itemCount As Integer = 0
    Dim itemCountCookie As HttpCookie = _
           HttpContext.Current.Request.Cookies("ItemCount")
    If (Not itemCountCookie Is Nothing) Then
      itemCount = Convert.ToInt32(itemCountCookie.Value)
    Else
      itemCountCookie = New HttpCookie("ItemCount")
      itemCountCookie.Value = "0"
      HttpContext.Current.Response.Cookies._
                                   Add(itemCountCookie)
    End If

    Dim cart As ArrayList = New ArrayList()
    Dim i As Integer
    Dim cn As String
    For i = 0 To itemCount - 1
      cn = i.ToString() & "cost"
      Dim cost As Integer = Convert.ToInt32( _
             HttpContext.Current.Request.Cookies(cn).Value)

      cn = i.ToString() & "desc"
      Dim desc As String = _  
             HttpContext.Current.Request.Cookies(cn).Value
      cart.Add(New Item(desc, cost))
    Next i

    Return cart
  End Function

  Public Shared Sub SaveArrayListToCookies(_
                                   ByVal cart As ArrayList)

    ' Save array size first
    Dim itemCountCookie As HttpCookie = _
                                New HttpCookie("ItemCount")
    itemCountCookie.Value = cart.Count.ToString()
    HttpContext.Current.Response.Cookies.Add( _
                                           itemCountCookie)

    Dim i As Integer = 0
    Dim it As Item
    For Each it In cart
      Dim descCookie As HttpCookie = _
                     New HttpCookie(i.ToString() + "desc")
      descCookie.Value = it.Description
      HttpContext.Current.Response.Cookies.Add(descCookie)

      Dim costCookie As HttpCookie = _
                    New HttpCookie(i.ToString() & "cost")
      costCookie.Value = it.Cost.ToString()
      HttpContext.Current.Response.Cookies.Add(costCookie)
      i = i + 1
    Next it
  End Sub
  ' remainder of class unchanged from Listing 10-4
End Class

Listing 10-19: Cookie State Shopping Page Example

Public Class PurchasePage 
  Inherits Page

    ' Maintain private cart array variable
  Private m_Cart As ArrayList

  Private Sub Page_Load(ByVal sender As Object, _
                        ByVal e As EventArgs)
    m_Cart = Item.HydrateArrayListFromCookies()
  End Sub


  Private Sub Page_PreRender(ByVal sender As Object, _
                             ByVal e As EventArgs) _
                             Handles MyBase.PreRender
    Item.SaveArrayListToCookies(m_Cart)
  End Sub
 
  Private Sub AddItem(ByVal desc As String, _
                      ByVal cost As Integer)
    m_Cart.Add(New Item(desc, cost))
  End Sub

  ' remaining code identical to Listing 10-7
End Class

Although it is technically possible to store any type of client-specific state using cookies, as shown in the previous shopping cart example, there are several drawbacks compared with other models. First, all of the state must be mapped into and out of strings, which in general requires more space to store the same amount of data. Second, as mentioned earlier, clients may disable cookies or may have a browser that does not support cookies, thus rendering the application inoperative. Finally, unlike session state, cookie state is passed between the client and the server with every request.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020