I just posted this on the curl-library list, but I feel it suits to be mentioned here separately.

As I’ve mentioned before, I’m involved in the IETF http-state working group which is working to document how cookies are used in the wild today. The idea is to create a spec that new implementations can follow and that existing implementations can use to become more interoperable.

(If you’re interested in these matters, I can only urge you to join the http-state mailing list and participate in the discussions.)

The subject of how to order cookies in outgoing HTTP Cookie: headers have been much debated over the recent months and I’ve also blogged about it. Now, the issue has been closed and the decision went quite opposite to my standpoint and now the spec will say that while the servers SHOULD not rely on the order (yeah right, some obviously already do and with this specified like this even more will soon do the same) it will recommend clients to sort the cookies in a given way that is close to the way current Firefox does it[*].

This has the unfortunate side-effect that to become fully compatible with how the browsers do cookies, we will need to sort our cookies a bit more than what we just recently introduced. That in itself really isn’t very hard since once we introduced qsort() it is easy to sort on more/other keys.

The biggest problem we get with this, is that the sorting uses creation time of the cookies. libcurl and curl and others mostly use the Netscape cookie files to store cookies and keep state between invokes, and that file format doesn’t include creation time info! It is a simple text-based file format with TAB-separated columns and the last (7th) column is the cookie’s content.

In order to support the correct sorting between sessions, we need to invent a way to pass on the creation time. My thinking is that we do this in a way that allows older libcurls still understand the file but just not see/understand the creation time, while newer versions will be able to get it. This would be possible by extending the expires field (the 6th) as it is a numerical value that the existing code will parse as a number and it will stop at the first non-digit character. We could easily add a character separation and store the
creation time after. Like:

Old expire time:

2345678

New expire+creation time:

2345678/1234567

This format might even work with other readers of this file format if they do similar assumptions on the data, but the truth is that while we picked the format in the first place to be able to exchange cookies with a well known and well used browser, no current browser uses that format anymore. I assume there are still a bunch of other tools that do, like wget and friends.

Update: as my friend Micah Cowan explains: we can in fact use the order of the cookie file as “creation time” hint and use that as basis for sorting. Then we don’t need to modify the file format. We just need to make sure to store them in time-order… Internally we will need to keep a line number or something per cookie so that we can use that for sorting.

[*] – I believe it sorts on path length, domain length and time of creation, but as soon as the -06 draft goes online it will be easy to read the exact phrasing. The existing -05 draft exists at: http://tools.ietf.org/html/draft-ietf-httpstate-cookie-05