Some websites stopped working today or at least some cookie-based functions ran out-of-order. Deleting all cookies helps - but is no solution. A cookie called __atrfs set by the famous AddThis! service is responsible for this.

First: The problem has been reported to and answered by the AddThis support.

The cookie violated the specifications by containing invalid chars. They tried to fix it by setting the Cookie to an empty value - which is usually ok, but results in unexpected problems with CGI::PSGI (and maybe also the plain CGI module).

The CGI module returns a list of the cookie names using the ->cookies() method. I used to build a cookie hash by using the following code snipped:

$self->{cookies} = { map { $_, $q->cookie($_); } ( $q->cookie() ) };

The fixed __atrfs cookie has no value at all (which also violates the specs, I think, because an empty cookie should be deleted) and the ->cookie($_) method returns neither undef nor am empty value for empty cookies - but an empty list (in array context). My map call returns just the cookie name __atrfs but no second argument breaking the hash, because the next cookie name would be used as the value for __atrfs.

The bugfix was very easy:

$self->{cookies} = { map { $_, scalar($q->cookie($_)); } ( $q->cookie() ) };

The scalar function always returns one item (which may be undef, but that's perfectly ok).