Check if Cookie Exists

Question

From a quick search on Stack Overflow I saw people suggesting the following way of checking if a cookie exists   HttpContext Current Response Cookies  cookie name      null   or  inside a Page class    this Response Cookies  cookie name      null   However  when I try to use the indexer  or the Cookies Get method  to retrieve a cookie that does not exist it seems to actually create a  default  cookie with that name and return that  thus no matter what cookie name I use it never returns null   and even worse - creates an unwanted cookie   Am I doing something wrong here  or is there a different way of simply checking for the existance of a specific cookie by name

User · Answer

You need to use HttpContext Current Request Cookies  not Response Cookies   Side note  cookies are copied to Request on Response Cookies Add  which makes check on either of them to behave the same for newly added cookies  But incoming cookies are never reflected in Response   This behavior is documented in HttpResponse Cookies property      After you add a cookie by using the HttpResponse Cookies collection  the cookie is immediately available in the HttpRequest Cookies collection  even if the response has not been sent to the client

User · Answer

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

User · Answer

public static class CookieHelper            lt summary gt          Checks whether a cookie exists           lt  summary gt           lt param name  cookieCollection  gt A CookieCollection  such as Response Cookies  lt  param gt           lt param name  name  gt The cookie name to delete  lt  param gt           lt returns gt A bool indicating whether a cookie exists  lt  returns gt      public static bool Exists this HttpCookieCollection cookieCollection  string name                if  cookieCollection    null                        throw new ArgumentNullException  cookieCollection                       return cookieCollection name     null            Usage   Request Cookies Exists  MyCookie

User · Answer

Sorry  not enough rep to add a comment  but from zmbq s answer      Anyway  to see if a cookie exists  you can check Cookies Get string   this will not modify the cookie collection    is maybe not fully correct  as Cookies Get string  will actually create a cookie with that name  if it does not already exist   However  as he said  you need to be looking at Request Cookies  not Response Cookies So  something like   bool cookieExists   HttpContext Current Request Cookies  cookie name      null

User · Answer

You can do something like this to find out the cookies s value   Request Cookies SESSION COOKIE NAME  Value

User · Answer

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

User · Answer

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

[c#] Check if Cookie Exists

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