ASP.NET Cookies Overview

A cookie is a small bit of text that accompanies requests and pages as they go between the Web server and browser. The cookie contains information the Web application can read whenever the user visits the site.

Scenarios

Cookies provide a means in Web applications to store user-specific information. For example, when a user visits your site, you can use cookies to store user preferences or other information. When the user visits your Web site another time, the application can retrieve the information it stored earlier.

For example, if a user requests a page from your site and your application sends not just a page, but also a cookie containing the date and time, when the user’s browser gets the page, the browser also gets the cookie, which it stores in a folder on the user’s hard disk.

Later, if user requests a page from your site again, when the user enters the URL the browser looks on the local hard disk for a cookie associated with the URL. If the cookie exists, the browser sends the cookie to your site along with the page request. Your application can then determine the date and time that the user last visited the site. You might use the information to display a message to the user or check an expiration date.

Cookies are associated with a Web site, not with a specific page, so the browser and server will exchange cookie information no matter what page the user requests from your site. As the user visits different sites, each site might send a cookie to the user’s browser as well; the browser stores all the cookies separately.

You can add cookies to the Cookies collection in a number of ways. The following example shows two methods to write cookies:

Response.Cookies["userName"].Value = "patrick";
Response.Cookies["userName"].Expires = DateTime.Now.AddDays(1);

HttpCookie aCookie = new HttpCookie("lastVisit");
aCookie.Value = DateTime.Now.ToString();
aCookie.Expires = DateTime.Now.AddDays(1);
Response.Cookies.Add(aCookie);

To create a cookie with subkeys, you can use a variation of the syntax for writing a single cookie. The following example shows two ways to write the same cookie, each with two subkeys:

Response.Cookies["userInfo"]["userName"] = "patrick";
Response.Cookies["userInfo"]["lastVisit"] = DateTime.Now.ToString();
Response.Cookies["userInfo"].Expires = DateTime.Now.AddDays(1);

HttpCookie aCookie = new HttpCookie("userInfo");
aCookie.Values["userName"] = "patrick";
aCookie.Values["lastVisit"] = DateTime.Now.ToString();
aCookie.Expires = DateTime.Now.AddDays(1);
Response.Cookies.Add(aCookie);

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.
Limiting Cookies to a Folder or Application
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);

Limiting Cookie Domain Scope

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

Reading Cookies

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

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

 

 

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