Check if Cookie Exists

Sometimes you still need to know if Cookie exists in Response. Then you can check if cookie key exists:

HttpContext.Current.Response.Cookies.AllKeys.Contains("myCookie")

More info can be found here.

In my case I had to modify Response Cookie in Application_EndRequest method in Global.asax. If Cookie doesn't exist I don't touch it:

string name = "myCookie";HttpContext context = ((HttpApplication)sender).Context;HttpCookie cookie = null;if (context.Response.Cookies.AllKeys.Contains(name)){    cookie = context.Response.Cookies[name];}if (cookie != null){    // update response cookie}

There are a lot of right answers here depending on what you are trying to accomplish; here's my attempt at providing a comprehensive answer:

Both the Request and Response objects contain Cookies properties, which are HttpCookieCollection objects.

Request.Cookies:

• This collection contains cookies received from the client
• This collection is read-only
• If you attempt to access a non-existent cookie from this collection, you will receive a null value.

Response.Cookies:

• This collection contains only cookies that have been added by the server during the current request.
• This collection is writeable
• If you attempt to access a non-existent cookie from this collection, you will receive a new cookie object; If the cookie that you attempted to access DOES NOT exist in the Request.Cookies collection, it will be added (but if the Request.Cookies object already contains a cookie with the same key, and even if it's value is stale, it will not be updated to reflect the changes from the newly-created cookie in the Response.Cookies collection.

Solutions

If you want to check for the existence of a cookie from the client, do one of the following

• Request.Cookies["COOKIE_KEY"] != null
• Request.Cookies.Get("COOKIE_KEY") != null
• Request.Cookies.AllKeys.Contains("COOKIE_KEY")

If you want to check for the existence of a cookie that has been added by the server during the current request, do the following:

• Response.Cookies.AllKeys.Contains("COOKIE_KEY") (see here)

Attempting to check for a cookie that has been added by the server during the current request by one of these methods...

• Response.Cookies["COOKIE_KEY"] != null
• Response.Cookies.Get("COOKIE_KEY") != null (see here)

...will result in the creation of a cookie in the Response.Cookies collection and the state will evaluate to true.

Response.Cookies contains the cookies that will be sent back to the browser. If you want to know whether a cookie exists, you should probably look into Request.Cookies.

Anyway, to see if a cookie exists, you can check Cookies.Get(string). However, if you use this method on the Response object and the cookie doesn't exist, then that cookie will be created.

See MSDN Reference for HttpCookieCollection.Get Method (String)