Hello Everyone,

I'm creating an FFI that requires writing to and reading from a C (char *) buffer. The buffer may contain arbitrary binary data (not necessarily a character string). I wrote a few procedures (see below) to copy the data to and from a u8vector so I can operate on it using ports.

I'm hoping for comments or suggestions from you all about the code. Is there a cleaner/better/faster way to do this? Ideally there would be some way to open a byte-port directly to the buffer so it wouldn't have to be copied. Is this possible?

Thanks in advance,

-Ben

;; Typical use of this code:

(with-input-from-u8vector (c-buffer->u8vector foreign-pointer-to-pointer 0 buffer-size ) (lambda () ...))

(u8vector->c-buffer (with-output-to-u8vector '(char-encoding: ASCII) (lambda () ...)) foreign-pointer-to-buffer 0 buffer-size)

;; The code

(declare (fixnum) (not safe))

(c-declare #<<eo-declare

typedef const char * const_char_ptr;

eo-declare )

(c-define-type const-char-buffer "const_char_ptr") (c-define-type size-type unsigned-int32) ; Using -D_FILE_OFFSET_BITS=64 makes off_t 8 bytes instead of 4 (c-define-type offset-type "off_t" "S64_TO_SCMOBJ" "SCMOBJ_TO_S64" #f)

(define u8vector->c-buffer (c-lambda (scheme-object (pointer char) offset-type size-type) void #<<end-lambda

off_t i; ___U8 c; for (i = 0; i < ___arg4; i++) { ___SCMOBJ_to_U8(___U8VECTORREF(___arg1, ___FIX(i)), &c, i); ___CAST(char *,___arg2)[i + ___arg3] = c; } end-lambda ))

(define %c-buffer->u8vector (c-lambda (const-char-buffer scheme-object offset-type size-type) void #<<end-lambda

off_t i; ___SCMOBJ c; ___U8* buff = ___CAST(___U8*, ___arg1); for (i = 0; i < ___arg4; i++) { ___U8_to_SCMOBJ(buff[i + ___arg3], &c, i); ___U8VECTORSET(___arg2, ___FIX(i), c); }

end-lambda ))

(define (c-buffer->u8vector buff offset size) (let ((v (make-u8vector size))) (%c-buffer->u8vector buff v offset size) v))