CookieContainer 混淆

Question

据我了解，CookieContainer通过HttpWebRequests持久化cookie的基本用法如下：

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

然后：

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

但我无法理解这个过程背后的逻辑。变量 cookies 在初始化后似乎没有在任何地方重新分配。第一个 WebResponse 中的 cookie 究竟是如何传送到第二个 WebRequest 中的？

Answer 1

这是因为当您从网站检索响应时，它会自动填充您用于请求的 cookie 容器。您可以通过查看响应前后存在哪些 cookie 来测试这一点：

//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();