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Using Cookies in ASP.NET Options
@2016-02-16 21:42:52

Controlling Cookie Scope

By default, all cookies for a site are stored together on the client, and all cookies are sent to the server with any request to that site. In other words, every page in a site gets all of the cookies for that site. However, you can set the scope of cookies in two ways:

  • Limit the scope of cookies to a folder on the server, which allows you to limit cookies to an application on the site
  • Set scope to a domain, which allows you to specify which subdomains in a domain can access a cookie.

To limit cookies to a folder on the server, set the cookie's Path property, as in the following example:

HttpCookie appCookie = new HttpCookie("AppCookie");
appCookie.Value = "written " + DateTime.Now.ToString();
appCookie.Expires = DateTime.Now.AddDays(1);
appCookie.Path = "/Application1";
Response.Cookies.Add(appCookie);

The path can either be a physical path under the site root or a virtual root. The effect will be that the cookie is available only to pages in the Application1 folder or virtual root. For example, if your site is called www.contoso.com, the cookie created in the previous example will be available to pages with the path http://www.contoso.com/Application1/ and to any pages beneath that folder. However, the cookie will not be available to pages in other applications such as http://www.contoso.com/Application2/ or just http://www.contoso.com/.

In some browsers, the path is case sensitive. You cannot control how users type URLs into their browsers, but if your application depends on cookies tied to a specific path, be sure that the URLs in any hyperlinks you create match the case of the Path property value.

By default, cookies are associated with a specific domain. For example, if your site is www.contoso.com, the cookies you write are sent to the server when users request any page from that site. (This might not include cookies with a specific path value.) If your site has subdomains—for example, contoso.com, sales.contoso.com, and support.contoso.com—then you can associate cookies with a specific subdomain. To do so, set the cookie's Domain property, as in this example:

Response.Cookies["domain"].Value = DateTime.Now.ToString();
Response.Cookies["domain"].Expires = DateTime.Now.AddDays(1);
Response.Cookies["domain"].Domain = "support.contoso.com";

When the domain is set in this way, the cookie will be available only to pages in the specified subdomain. You can also use the Domain property to create a cookie that can be shared among multiple subdomains, as shown in the following example:

Response.Cookies["domain"].Value = DateTime.Now.ToString();
Response.Cookies["domain"].Expires = DateTime.Now.AddDays(1);
Response.Cookies["domain"].Domain = "contoso.com";

The cookie will then be available to the primary domain as well as to sales.contoso.com and support.contoso.com domains.

@2016-02-18 00:14:52

Reading Cookies

When a browser makes a request to the server, it sends the cookies for that server along with the request. In your ASP.NET applications, you can read the cookies using the HttpRequest object, which is available as the Request property of your Page class. The structure of the HttpRequest object is essentially the same as that of the HttpResponse object, so you can read cookies out of the HttpRequest object much the same way you wrote cookies into the HttpResponse object. The following code example shows two ways to get the value of a cookie named username and display its value in a Label control:

if(Request.Cookies["userName"] != null)
    Label1.Text = Server.HtmlEncode(Request.Cookies["userName"].Value);

if(Request.Cookies["userName"] != null)
{
    HttpCookie aCookie = Request.Cookies["userName"];
    Label1.Text = Server.HtmlEncode(aCookie.Value);
}

Before trying to get the value of a cookie, you should make sure that the cookie exists; if the cookie does not exist, you will get a NullReferenceException exception. Notice also that the HtmlEncode method was called to encode the contents of a cookie before displaying it in the page. This makes certain that a malicious user has not added executable script into the cookie.

Reading the value of a subkey in a cookie is likewise similar to setting it. The following code example shows one way to get the value of a subkey:

if(Request.Cookies["userInfo"] != null)
{
    Label1.Text = 
        Server.HtmlEncode(Request.Cookies["userInfo"]["userName"]);

    Label2.Text =
        Server.HtmlEncode(Request.Cookies["userInfo"]["lastVisit"]);
}

In the preceding example, the code reads the value of the subkey lastVisit, which was set earlier to the string representation of a DateTime value. Cookies store values as strings, so if you want to use the lastVisit value as a date, you have to convert it to the appropriate type, as in this example:

DateTime dt;
dt = DateTime.Parse(Request.Cookies["userInfo"]["lastVisit"]);

The subkeys in a cookie are typed as a collection of type NameValueCollection. Therefore, another way to get an individual subkey is to get the subkeys collection and then extract the subkey value by name, as shown in the following example:

if(Request.Cookies["userInfo"] != null)
{
    System.Collections.Specialized.NameValueCollection
        UserInfoCookieCollection;
      
    UserInfoCookieCollection = Request.Cookies["userInfo"].Values;
    Label1.Text =
        Server.HtmlEncode(UserInfoCookieCollection["userName"]);
    Label2.Text =
        Server.HtmlEncode(UserInfoCookieCollection["lastVisit"]);
}
@2016-02-18 08:16:50

Changing a Cookie's Expiration Date

The browser is responsible for managing cookies, and the cookie's expiration time and date help the browser manage its store of cookies. Therefore, although you can read the name and value of a cookie, you cannot read the cookie's expiration date and time. When the browser sends cookie information to the server, the browser does not include the expiration information. The cookie's Expires property in the HttpRequest object always returns a date-time value of zero. However, you can read the Expires property of a cookie that you have set in the HttpResponse object, before the cookie has been sent to the browser. If you are concerned about the expiration date of a cookie, you must reset it by creating a new cookie with the same name as the cookie to be deleted and set the cookie's expiration to a date you expect

@2016-02-22 08:55:49

Reading Cookie Collections

You might occasionally need to read through all the cookies available to the page. To read the names and values of all the cookies available to the page, you can loop through the Cookies collection using code such as the following.

System.Text.StringBuilder output = new System.Text.StringBuilder();
HttpCookie aCookie;
for(int i=0; i<Request.Cookies.Count; i++)
{
    aCookie = Request.Cookies[i];
    output.Append("Cookie name = " + Server.HtmlEncode(aCookie.Name)
        + "<br />");
    output.Append("Cookie value = " + Server.HtmlEncode(aCookie.Value)
        + "<br /><br />");
}
Label1.Text = output.ToString();

A limitation of the preceding example is that if the cookie has subkeys, the display shows the subkeys as a single name/value string. You can read a cookie's HasKeys property to determine whether the cookie has subkeys. If so, you can read the subkey collection to get individual subkey names and values. You can read subkey values from the Values collection directly by index value. The corresponding subkey names are available in the AllKeys member of the Values collection, which returns an array of strings. You can also use the Keys member of the Values collection. However, the AllKeys property is cached the first time it is accessed. In contrast, the Keys property builds an array each time it is accessed. For this reason, the AllKeys property is much faster on subsequent accesses within the context of the same page request.

The following example shows a modification of the preceding example. It uses the HasKeys property to test for subkeys, and if subkeys are detected, the example gets subkeys from the Values collection:

for(int i=0; i<Request.Cookies.Count; i++)
{
    aCookie = Request.Cookies[i];
    output.Append("Name = " + aCookie.Name + "<br />");
    if(aCookie.HasKeys)
    {
        for(int j=0; j<aCookie.Values.Count; j++)
        {
            subkeyName = Server.HtmlEncode(aCookie.Values.AllKeys[j]);
            subkeyValue = Server.HtmlEncode(aCookie.Values[j]);
            output.Append("Subkey name = " + subkeyName + "<br />");
            output.Append("Subkey value = " + subkeyValue +
                "<br /><br />");
        }
    }
    else
    {
        output.Append("Value = " + Server.HtmlEncode(aCookie.Value) +
            "<br /><br />");
    }
}
Label1.Text = output.ToString();

Alternatively, you can extract the subkeys as a NameValueCollection object as shown in the following example:

System.Text.StringBuilder output = new System.Text.StringBuilder();
HttpCookie aCookie;
string subkeyName;
string subkeyValue;

for (int i = 0; i < Request.Cookies.Count; i++)
{
    aCookie = Request.Cookies[i];
    output.Append("Name = " + aCookie.Name + "<br />");
    if (aCookie.HasKeys)
    {
        System.Collections.Specialized.NameValueCollection CookieValues =
            aCookie.Values;
        string[] CookieValueNames = CookieValues.AllKeys;
        for (int j = 0; j < CookieValues.Count; j++)
        {
            subkeyName = Server.HtmlEncode(CookieValueNames[j]);
            subkeyValue = Server.HtmlEncode(CookieValues[j]);
            output.Append("Subkey name = " + subkeyName + "<br />");
            output.Append("Subkey value = " + subkeyValue +
                "<br /><br />");
        }
    }
    else
    {
        output.Append("Value = " + Server.HtmlEncode(aCookie.Value) +
            "<br /><br />");
    }
}
Label1.Text = output.ToString();
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