CookieContainer confusion

Question

From what I understand, the basic use of the CookieContainer to persist cookies through HttpWebRequests is as follows:

HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
CookieContainer cookies = new CookieContainer();
request.CookieContainer = cookies;
using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())
{
  // Do stuff with response
}

then:

request = (HttpWebRequest)WebRequest.Create(new url);
request.CookieContainer = cookies;
etc...

But I'm having trouble understanding the logic behind this process. The variable cookies doesn't seem to have been reassigned anywhere after its initialization. How exactly do the cookies from the first WebResponse carry into the second WebRequest?

Solution

It's because when you retrieve the response from the website, it automatically populates the cookie container you used for the request. You can test this out by seeing what cookies are present before and after the response:

//Build the request
Uri site = new Uri("http://www.google.com");
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(site);
CookieContainer cookies = new CookieContainer();
request.CookieContainer = cookies;

//Print out the number of cookies before the response (of course it will be blank)
Console.WriteLine(cookies.GetCookieHeader(site));

//Get the response and print out the cookies again
using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())
{
    Console.WriteLine(cookies.GetCookieHeader(site));
}

Console.ReadKey();

Comments

[Drazen Bjelovuk]

I see. Then would I be right to say that the statement "request.CookieContainer = cookies;" is simply passing a reference of the object "cookies" to request.CookieContainer rather than the data itself?

[Ichabod Clay]

That sounds about right. If you need some brushing up on passing references/values, take a look at this article.

[Drazen Bjelovuk]

Very much appreciated. Thank you. =)