ASP.NET Tricks

Today I had to develop very simple and standard functionality with cookies. I’ll describe this shortly.

Task
When user visits a site for the first time a disclaimer page must be displayed. Once the user agree with it a cookie value is changed to “true” and the next time the user opens the site the disclaimer is not displayed.

Problem
The cookie is lost when the browser is closed if you change cookie value.

Research
Below is some example code that I used to investigate the problem:

1. Open Visual Studio
2. Create new web site
3. Copy and paste the following code to the Page_Load method of defaut.aspx.cs file:

   if (Request.Cookies["test"] == null)
   {
     HttpCookie cookieDisclaimer = new HttpCookie("test", "cookie test");
     cookieDisclaimer.Expires = DateTime.MaxValue; // the cookie never expires
     Response.Cookies.Add(cookieDisclaimer);
   
     Response.Write("cookie added");
   }
   else
   {
     // NOTE: We'll add some lines here later
     Response.Write(Request.Cookies["test"].Value);
   }
   

4. Buld the website and open in a browser
5. The first time the browser opens the cookie is created. Click F5 several times and you’ll see cookie value displayed.
6. Close the browser, open it again and navigate to the website URL. You’ll see directly the the cookie value which means that the cookie exists.

Now let’s update the code, so cookie value is changed.
Add the following code below “NOTE: We’ll add some lines here later”:

Response.Cookies["test"].Value = "cookie test";

Execute the steps described above and you’ll see that every time you open a browser the cookie is created. So the cookie expires when the browser is closed.

According to me this is not the correct cookie behaviour. Correct me if I’m wrong

Solution
The solution is simple: everytime you change the cookie value, you need to set cookie expiration date too.

So adding the following code after “NOTE: We’ll add some lines here later” fix the problem:

Response.Cookies["test"].Value = "cookie test";
Response.Cookies["test"].Expires = DateTime.MaxValue;

I hope the solution above is useful.