sb-impl:read-from-c-string/* report undecodable octets incorrectly

[3b]

(cffi:with-foreign-string (a (string (code-char #xff)) :encoding :iso-8859-1)
  (sb-impl::read-from-c-string/ascii a 'character))

gives the error:

c-string decoding error (:external-format :ASCII):
  the octet sequence 1 cannot be decoded.
   [Condition of type SB-INT:C-STRING-DECODING-ERROR]

expected something describing the octets that could not be decoded (#xff in this case) rather than always 1

(cffi:with-foreign-string (a (string (code-char #xff)) :encoding :iso-8859-1)
  (sb-impl::read-from-c-string/utf-8 a 'character))

produces
c-string decoding error (:external-format :UTF-8):
  the octet sequence 4 cannot be decoded.
   [Condition of type SB-INT:C-STRING-DECODING-ERROR]

the '4' in the error message varies from 1 to 4 depending on the octet sequence, but still doesn't not show the actual octets

tested on "1.0.45.13", x8664 linux

[Nikodemus Siivola (nikodemus)]

Looks like there's confusion re. meaning of DECODE-BREAK-REASON in the source.

[Douglas Katzman (dougk)]

This was fixed sufficiently long ago that I don't know when.
It now prints:

#<THREAD "main thread" RUNNING {D8E6F0C9}>:
  :ASCII c-string decoding error: the octet sequence #(255) cannot be decoded.