[armedbear-devel] MAKE-IMMEDIATE-OBJECT and JOBJECT-LISP-VALUE conceptual problem

[Mark Evenson]

Today, I spent a bit of time trying to figure out a way to efficiently 
compute message digest for Quicklisp.  After confirming that 
java.security.MessageDigest implements the required digests, I noticed 
we didn't have a way to easily get at the underlying Java byte[] array 
in (SIMPLE-VECTOR (UNSIGNED-BYTE 8)).  So, I patched the underlying Java 
code as attached, and wrote the following routine:

(defun sha-256 (path)
   (let ((buffer (make-array 8192 :element-type '(unsigned-byte 8))
           (digest (jstatic "getInstance" "java.security.MessageDigest" 
"SHA-256")))
         (with-open-file (in path :element-type '(unsigned-byte 8))
           (loop :for bytes = (read-sequence buffer in)
              :while (plusp bytes)
              :do (jcall-raw "update" digest (make-immediate-object 
buffer) 0 bytes))
           (jcall "digest" digest)))))

But then I noticed that MAKE-IMMEDIATE-OBJECT calls JOBJECT-LISP-VALUE 
which makes no conceptual sense.  The doc for MAKE-IMMEDIATE-OBJECT 
reads "[a]ttempts to coerce a given Lisp object into a java-object" 
while the doc JOBJECT-LISP-VALUE reads "Attempts to coerce JAVA-OBJECT 
into a Lisp object".   This seems wrong here, but I don't understand how 
exactly.  I think we need to distinguish three types of values here: 
JAVA-OBJECT, LispObject, and the "raw" value of the Java.  How should we 
really structure our Java FFI here?

With my patch, for an underlying lisp value of type (SIMPLE-VECTOR 
(UNSIGNED-BYTE 8)), both MAKE-IMMEDIATE-OBJECT and JOBJECT-LISP-OBJECT 
return the byte[] array.  I would think that MAKE-IMMEDIATE-OBJECT 
should just do this, which JOBJECT-LISP-OBJECT should .... return an 
error if its argument isn't of type JAVA-OBJECT?  I don't know.  I am 
confused.

Can someone help me understand the right way forward here?

-- 
"A screaming comes across the sky.  It has happened before, but there
is nothing to compare to it now."
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