There are several, with http://www.civicuk.com/cookie-law/index and http://silktide.com/cookieconsent being the most popular afaik.

If your server sends cookies automatically, it would fall foul of this Spanish implementation of the law (supposedly). Implied consent does not cover simply giving the users information, and some of the cookies being argued over are third-party too. There's no third-party snippet you can drop in and "fix" this for Google Analytics (for example).

You actually need to avoid cookies getting stored until users give their consent to do so. Probably something like the rack-policy Ruby gem linked below will help making sure there is no cookies at all.

https://github.com/peter-murach/rack-policy#rack-policy

I ignore if there are similar libraries for other platforms.