I am observing, on both Firefox and IE, that if I have a cookie 'x' on the domain a.b.c.com, and also have a cookie with the same name 'x' on domain a.b.com, then when I look at the value of document.cookie on the a.b.c.com domain, it shows both cookies. I would like to see just the cookie from the a.b.c.com domain, and not the one from the other domain. (I'm assuming this occurs because one domain is the same as the other one, with an additional segment on the hostname.) Is there a way to do this?
I don't have control over the contents of the cookie, and I don't see anything obvious in those contents that distinguishes one domain from the other.
You don't have access to the domain of the cookie in Javascript.
"When [the cookie] attribute is read, all
cookies are returned as a single
string, with each cookie's name-value
pair concatenated into a list of
name-value pairs, each list item being
separated by a ';' (semicolon)."
W3C
When you read a cookie, you only have access to the name/value pairs, and cannot determine any other information about it. If you require things such as when it was set, what domains it was set for, or anything else, you have to store it inside the cookie value.
Since you cannot set the cookies, you need another method to do what you're attempting.
Related
Is there a good programmatic way to automatically set a cookie on the highest possible domain?
For example:
sub1.sub2.example.com -> example.com
sub1.sub2.example.co.uk -> example.co.uk
When setting a cookie using document.cookie = ... there is no error when trying to set a cookie for a domain that is "out of scope".
I guess I could iterate through each "level" and try to set a cookie there, so:
sub1.sub2.example.com
sub2.example.com
example.com
com
But I would only want the cookie to be set on example.com and not any of the subdomains.
If there was some kind of error, I could start from the bottom and stop when no exception occurs. But as there is no error, that does not work.
Or I guess I could compare document.cookie after each level (also starting from the bottom) and check if my desired value is set. But that also seems quite bad.
Are there any other good solutions?
Say for example I had an application sending the following HTTP headers to set to cookie named "a":
Set-Cookie: a=1;Path=/;Version=1
Set-Cookie: a=2;Path=/example;Version=1
If I access /example on the server both paths are valid, so I have two cookies named "a"! Since the browser doesn't send any path information, the two cookies cannot be distinguished.
Cookie: a=2; a=1
How should this case be handled? Pick the first one? Create a list with all cookie values? Or should such a case be considered as a developer's mistake?
The answer referring to an article on SitePoint is not entirely complete. Please see RFC 6265 (to be fair, this RFC was released in 2011 after this question was posted, which supersedes previous RFC 2965 from 2000 and RFC 2109 from 1997).
Section 5.4, subsection 2 has this to say:
The user agent SHOULD sort the cookie-list in the following order:
Cookies with longer paths are listed before cookies with shorter paths.
NOTE: Not all user agents sort the cookie-list in this order, but this
order reflects common practice when this document was written, and,
historically, there have been servers that (erroneously) depended on
this order.
There is also this little gem in section 4.2.2:
... servers SHOULD NOT rely upon the serialization order. In
particular, if the Cookie header contains two cookies with the same
name (e.g., that were set with different Path or Domain attributes),
servers SHOULD NOT rely upon the order in which these cookies appear in the header.
In your example request cookie (Cookie: a=2; a=1) note that the cookie set with the path /example (a=2) has a longer path than the one with the path / (a=1) and so it is sent back to you first in line, which matches the recommendation of the spec. Thus you are more or less correct in your assumption that you could select the first value.
Unfortunately the language used in RFCs is extremely specific - the use of the words SHOULD and SHOULD NOT introduce ambiguity in RFCs. These indicate conventions that should be followed, but are not required to be conformant to the spec. While I understand the RFC for this quite well, I haven't done the research to see what real-world clients do; it's possible one or more browsers or other softwares acting as HTTP clients may not send the longest-path cookie (eg: /example) first in the Cookie: header.
If you are in a position to control the value of the cookie and you want to make your solution foolproof, you are best off either:
using a different cookie name to override in certain paths, such as:
Set-cookie: a-global=1;Path=/;Version=1
Set-cookie: a-example=2;Path=/example;Version=1
storing the path you need in the cookie value itself:
Set-cookie: a=1&path=/;Path=/;Version=1
Set-cookie: a=2&path=/example;Path=/example;Version=1
Both of these workarounds require additional logic on the server to pick the desired cookie value, by comparing the requested URL against the list of available cookies. It's not too pretty. It's unfortunate the RFC did not have the foresight to require that a longer path completely overrides a cookie with a shorter path (eg: in your example, you would receive Cookie: a=2 only).
From this article on SitePoint:
If multiple cookies of the same name match a given request URI, one is chosen by the browser.
The more specific the path, the higher the precedence. However precedence based on other attributes, including the domain, is unspecified, and may vary between browsers. This means that if you have set cookies of the same name against “.example.org” and “www.example.org”, you can’t be sure which one will be sent back.
Edit: this information from 2010 appears to be outdated, it seems browsers can now send multiple cookies in return, see answer by #Nate below for details
#user2609094 clarifies the behaviour around paths, so I thought I'd add a quick answer for the behaviour around domains (which is unspecified).
If you create cookies for a domain and subdomain ("foo.example.org" and "example.org") with the same name then the browser will send both cookies, with no indication of which one is which. Additionally, the order does not appear to be based on which domain is more specific. From testing in Google Chrome, the cookies are simply sent in the order they were created - so you can't make any assumptions about which one is which.
There is nothing wrong with having multiple values for the same name... if you want them. You might even embed additional context in the value.
If you don't, then of course different names are a solution if you want both contexts.
The alternative is to send the same cookie name with the same path (and domain) even from the more specific paths. Those set cookie instructions will overwrite the value of that cookie.
Now that you know the most important part (how they work), and that you can accomplish what you need in a few different ways, my answer to your question is: this is a developer issue.
I'm certainly aware of applications which do this extensively using multiple session ids - and seem to work consistently. However I don't know - and have no intention of finding out - if they do so because the browser returns the cookies in a consistent order depending on when they were set / which path they were set for or whether the app tries to match each one to an existing session.
I would strongly recommend that this practice be avoided.
However if you really want to know how the browsers (and apps) handle this scenario, why not build a test rig and try it out.
If you use the Java/Scala framework Play: watch out! If a request contains multiple cookies with the same name, Play will only present 1 of them to your code.
If you need to distinguish them you have to give them different key values.
I recently had cookies set to a specific sub-domain (i.e. "cookie1" set to sub1.mysite.com). I then changed the code to write the same name cookie to the domain (i.e. "cookie1 set to .mysite.com). Now if I hit a page without clearing cookies, I see the two cookies with the same name but scoped differently. So my question is when on sub1.mysite.com, which cookie will be read due to two cookies existing with same name and both in scope?
Thanks,
MJ
The cookie with the most specific matching scope will be used. This allows a subdomain to override a domain-wide default cookie.
It doesn't seem that JS provide any ability off the bat to grab the value of a cookie based on the domain, but does anyone have a suggestion as to how this can be done?
For example:
There may be two cookies with the same name, but one is set globally across all pages (.example.com) and the other is set on a certain page (sub.example.com).
document.cookie
will only retrieve a string of all the cookie key:value pairs, with no association to the appropriate domain. ex:
"this_cookie=abc; that_cookie=xyz; this_cookie=123"
I would like to grab the cookie which is instantiated on the subdomain (this_cookie #2)
document.cookie does not expose the domain information as you can see for yourself.
Just an idea: Maybe you can store document.cookie temporarily, then override the cookie for the subdomain and compare again with document.cookie to see which has changed.
But to be honest: Can you not put the subdomain into the cookie name or value?
You cannot. or there will be security vulnerabilities.
When you setup the cookie on subdomain, you have to set "globally across all pages (.example.com)" so that you can retrieve it from the main domain.
I am dealing with a third party JavaScript code that sets a cookie through document.cookie= but without using the key=value format ; instead of doing document.cookie="mykey=myvalue" it does document.cookie="10254/1/19,20,/0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,//20".
This leads to issue on my server side code, as Chrome and Firefox send this to my server as a cookie without name and with value "10254/1/19,20,/0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,//20". Safari sends a series of cookies without values and with names "10254/1//0,//-1", "10254/1//0,1,//-1", "10254/1//0,1,2,//-1", etc.
Is it legal to set a cookie without the format key=value? I've read https://www.rfc-editor.org/rfc/rfc6265#section-4.1.1 and seen cookie-pair = cookie-name "=" cookie-value but it is not clear for me whether = is mandatory. I think it is, just would like a confirmation.
Answering myself: cookies without = should be ignored by the user agent. From http://trac.tools.ietf.org/wg/httpstate/trac/ticket/1
Per discussion on the mailing list and at IETF77, I've removed nameless cookies from the draft. Cookies without names (either because they lack a "=" or because "=" occurs as the first character of the set-cookie-string") are now ignored by the user agent.
But in practice browsers do send cookies whose name-value-pair does not contain =. They do not have the same behavior though: for instance if I set a cookie with document.cookie("foo"), Safari will send to the server a cookie with name "foo" and a blank value, while Chrome will send a cookie with a blank name a the value "foo".