How do I convert the Cookies collection to a generic list? Easily

Question

Anyone know how I can convert Request.Cookies into a List<HttpCookie>? The following didn't work as it throws an exception.

List<HttpCookie> lstCookies = new List<HttpCookie>(
    Request.Cookies.Cast<HttpCookie>());

Exception: Unable to cast object of type 'System.String' to type 'System.Web.HttpCookie'

Cranwell

Answer 1

The reason this happens is because the NameObjectCollectionBase type that Request.Cookies derives from enumerates over the keys of the collection and not over the values. So when you enumerate over the Request.Cookies collection you are getting the keys:

public virtual IEnumerator GetEnumerator()
{
    return new NameObjectKeysEnumerator(this);
}

This means that the following will work:

string[] keys = Request.Cookies.Cast<string>().ToArray();

I guess you could try the following which might be considered ugly but will work:

List<HttpCookie> lstCookies = Request.Cookies.Keys.Cast<string>()
    .Select(x => Request.Cookies[x]).ToList();

---

UPDATE:

As pointed out by @Jon Benedicto in the comments section and in his answer using the AllKeys property is more optimal as it saves a cast:

List<HttpCookie> lstCookies = Request.Cookies.AllKeys
    .Select(x => Request.Cookies[x]).ToList();

Atkins

But then you lose the key -> value connection :) – Goldia

@Snake, I agree with you that this is not optimal from performance standpoint as it will enumerate the collection multiple times but if you have a couple of elements it might not be dramatical. – Atkins

Using the AllKeys member of HttpCookieCollection saves a cast. See my answer for code. – Sonasonant

This helped me solve an issue with XmlSerializer serializing the keys and not the values. My NameObjectCollectionBase subclass needed to override GetEnumerator as return this.BaseGetValues().GetEnumerator(); – Adonai

Note when 2 cookies with the same key is received (a=1; a=2) Response.Cookies[string] always return the first one (a=1). Instead you need to use something like Request.Cookies.AllKeys.Select((_, x) => Request.Cookies[x]) – Virginity

Answer 2

If you really want a straight List<HttpCookie> with no key->value connection, then you can use Select in LINQ to do it:

var cookies = Request.Cookies.AllKeys.Select(x => Request.Cookies[x]).ToList();

Sonasonant

IE can send multiple cookies with the same name if the cookies are created in separate domains. If this happens then the code above loses one of the cookies. – Slick

The code gets only the first cookie with the same name. – Fane

Answer 3

The question may be a bit old, but the answers here are not covering all cases, because as pointed out by @C.M. there can be multiple cookies with the same name.

So the easiest way is to loop the cookies collection with a for loop:

var existingCookies = new List<HttpCookie>();

for (var i = 0; i < _httpContext.Request.Cookies.Count; i++)
{
    existingCookies.Add(_httpContext.Request.Cookies[i]);
}

Bickford

Answer 4

.Cookies.Cast<HttpCookie>(); tries to cast the collection of keys to a collection of cookies. So it's normal that you get an error :)

It's a name -> value collection, so casting to a list wouldn't be good.

I would try converting it to a dictionary.

For example:

Since Cookies inherits from NameObjectCollectionBase you can GetAllKeys(), and use that list to get all the values and put them in a Dictionary.

For example:

Dictionary cookieCollection = new Dictionary<string, object>();

foreach(var key in Request.Cookies.GetAllKeys())
{
    cookieCollection.Add(key, Request.Cookies.Item[key]);
}

Goldia

Answer 5

You can avoid iterating the keys by using the collection's Count with Enumerable.Range.

using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace Foo
{
  public static class WebHttpExtensions
  {
    public static IEnumerable<HttpCookie> AsEnumerable(this HttpCookieCollection webCookies) =>
      Enumerable
        .Range(0, webCookies.Count)
        .Select(ndx => webCookies[ndx]);

    public static IEnumerable<System.Net.Cookie> ToNetCookies(this HttpCookieCollection webCookies) => 
      webCookies
        .AsEnumerable()
        .Select(x => new System.Net.Cookie(x.Name, x.Value));
  }
}

Bibbs