Drakma encodes spaces in URLs as pluses instead of "%20"s. It also leaves the characters "$-_.!*'()" unencoded instead of the RFC3986 unencoded set: "-_.~".

This is okay for tolerant servers but for other applications it is a bug. For example, in OAuth it is necessary to conform to RFC3986 or the signature will be incorrect for the request.

To make Drakma more RFC3986-compliant, replace these four lines in util.lisp:

                        (find char "$-_.!*'()," :test #'char=))
                     (write-char char out))
                   ((char= char #\Space)
                     (write-char #\+ out))

with these two:
                        (find char "-_.~" :test #'char=))
                     (write-char char out))

Best regards,
Red