C#: Writing a CookieContainer to Disk and Loading

Question

I have a CookieContainer extracted from a HttpWebRequest/HttpWebResponse session named CookieJar. I want my application to store cookies between runs, so cookies collected in the CookieContainer on one run of the program will be used the next run, too.

I think the way to do this would be to somehow write the contents of a CookieContainer to disk. My question is:

• How can you write a CookieContainer to the disk? Are there built-in functions for this, or, if not, what are the approaches people have taken? Are there any classes available for simplifying this?
• Once you've written a CookieContainer to the disk, how do you load it back in for use?

UPDATE: The first answer has suggested serialization of the CookieContainer. However, I am not very familiar with how to serialize and deserialize such complex objects. Could you provide some sample code? The suggestion was to utilise SOAPFormatter.

Answer 1

I Haven't tried it but it has the attribute Serializable and so can be [de]serialized with .net binary serialization, e.g. SoapFormatter.

Here is the code snippet you asked for.

var formatter = new SoapFormatter();
string file = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), "cookies.dat"); 

using (Stream s = File.Create (file))
    formatter.Serialize(s, cookies);                            
...
CookieContainer retrievedCookies = null;
using (Stream s = File.OpenRead (file))
    retrievedCookies = (CookieContainer) formatter.Deserialize(s);

Looking at msdn it seems SoapFormatter is now deprecated in .net 3.5 and it recommends you use Binaryformatter. In the past I have found SoapFormatter useful as the file is readable which helps with diagnosis when deserialization fails! These formatters are sensitive to version changes even in the assembly version (so if you deserialize with one version of the framework upgrade the framework, then it might not deserialize, not sure), but there are ways around this with the Binder property if this becomes a problem. I believe they are primarily designed for short term persistance / remoting, but they might be good enough for you here.

The new DataContractSerializer does not seem to work with it so that is out.

An alternative would be to write a CookieContainerData class to [de]serialize with XmlSerializer and manually convert between this and CookieContainer.

Answer 2

Another alternative is to use Json serialization (Json.NET):

// other includes
using Newtonsoft.Json;

A class with a cookie:

public class WithCookie
{
    public Cookie MyCookie { get; set; }

    public WithCookie()
    {
        MyCookie = new Cookie("CF788DF", "A cookie value!", "/", ".test.com");
    }
}

Here is how to serialize it to Json:

class Program
{
    static void Main(string[] args)
    {
        try
        {
            WithCookie wc1 = new WithCookie();
            // Expires a month from now
            wc1.MyCookie.Expires = DateTime.Now.AddMonths(1);

            string wc1json = JsonConvert.SerializeObject(new WithCookie());

            WithCookie wc2 = JsonConvert.DeserializeObject < WithCookie>(wc1json);

            string wc2json = JsonConvert.SerializeObject(wc2);

            if (wc2json == wc1json)
            {
                Console.WriteLine("HORRAY!");
            }
            else
            {
                // The strings will not be equal, because the Cookie.TimeStamp 
                // changes but the cookies are in fact the same!
                Console.WriteLine("FAIL!");
            }
        }
        catch (Exception e)
        {
            Console.WriteLine("Exception: " + e.ToString());
        }
        Console.ReadKey();
    }
}

Answer 3

This problem was bugging me for ages, nothing I could find worked. I worked it out, so putting that information out into the world.

Answer using BinaryFormatter:

    public static void WriteCookiesToDisk(string file, CookieContainer cookieJar)
    {
        using(Stream stream = File.Create(file))
        {
            try {
                Console.Out.Write("Writing cookies to disk... ");
                BinaryFormatter formatter = new BinaryFormatter();
                formatter.Serialize(stream, cookieJar);
                Console.Out.WriteLine("Done.");
            } catch(Exception e) { 
                Console.Out.WriteLine("Problem writing cookies to disk: " + e.GetType()); 
            }
        }
    }   

    public static CookieContainer ReadCookiesFromDisk(string file)
    {

        try {
            using(Stream stream = File.Open(file, FileMode.Open))
            {
                Console.Out.Write("Reading cookies from disk... ");
                BinaryFormatter formatter = new BinaryFormatter();
                Console.Out.WriteLine("Done.");
                return (CookieContainer)formatter.Deserialize(stream);
            }
        } catch(Exception e) { 
            Console.Out.WriteLine("Problem reading cookies from disk: " + e.GetType()); 
            return new CookieContainer(); 
        }
    }