[cffi-devel] Foreign string arguments

[Michael Raskin]

		Hello.
	I use callback feature of CFFI. I want to use an encoding as a default
and if I get an invalid string (non-UTF-8 in my case), I'd just reject
it by returning an error. Unfortunately, if I declare string arguments
with encoding, attempts by CFFI to decode the string raise an error
which prevents me from returning protocol-compliant error to the caller.

	The context: I currently work on FUSE bindings for Common Lisp (or at
least SBCL for now). In case of error occurring in my code, I return
EIO. Of course, for invalid file names I want to return either EIO or
ENOENT. Currently, request just hangs.

	This can be mitigated by patching CFFI. If I just wrap the conversion
in ignore-errors, I lose the distinction between an invalid string and
null pointer, but I get a chance to process the request (both cases are
wrong in my case). Specifying a designated "wrong string object" and
letting user change it seems to be the nicest way: the user gets an
error on trying to use the object as a string, but user code can handle
it nicely.

	I changed the following in string conversion code:

(defmethod translate-from-foreign (ptr (type foreign-string-type))
  (unwind-protect
       (block nil
           (handler-case
                (values (foreign-string-to-lisp ptr :encoding
(fst-encoding type)))
                (error (x) (return t))
                ))
    (when (fst-free-from-foreign-p type)
      (foreign-free ptr))))

	That allowed me to handle invalid requests to the FS by returning
ENOENT (just as originally intended).

	Would you please consider adding some similar modification in official
CFFI repository?

	Michael Raskin