I'm running into a problem with duplicated cookies. This is due to misbehaving servers sending back duplicate Set-Cookie headers in the same response, like this:

Set-Cookie: JSESSIONID=foo; Path=/; Secure
Set-Cookie: JSESSIONID=bar; Path=/; Secure

Firefox deals with this by picked the last cookie value specified. There is no logic in drakma currently to handle that, and so my cookie-jar is getting two JSESSION cookies, and further requests are sending both cookies. I do not control the servers returning me these duplicate headers.

This patch adds a unique-cookies function that iterates through cookie objects, keeping only the last one. This is then called in get-cookies to ensure no duplicate cookie objects are propagated to the rest of the system. I've got my "make it work on a friday afternoon" solution in the attached patch, but I'm not really happy with it long term, and wanted some advice. Problems I see:

I think the dolist/find combination is a recipe for performance problems with many cookies
It seems odd to build up a list of cookies, then rebuild it
The most common case of no duplicate cookies has an extra bunch of consing to rebuilding up the list
I think there should be a user choice of "ignore all but the last cookie" vs "ignore all but the first cookie" vs "leave them all in there"

Some thoughts on how to proceed:

Add a exported *redundant-cookie-strategy* variable, with values :keep-all, :keep-first, and :keep-last, defaulting to :keep-all (the current behavior).
remove the unique-cookies function and rewrite get-cookies to implement the *redundant-cookie-strategy*, making one pass through parsed-cookies.
leave get-cookies mostly as-is, but add some detection for duplicates, and run unique-cookies only if it we need to

Thanks,
Ryan

PS: I'm still kinda new to contributing on open source projects via emailed patches, sorry if this is in a bad format. I read http://weitz.de/patches.html and created this patch from my working copy using >diff -u ../drakma-1.1.0/cookies.lisp cookies.lisp