Hi Ben,
Ben Weaver wrote:
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?
Here's my attempt (below).
N.B. I'm going out on a limb here because I'm certainly no expert on gambit internals - this is just from looking at the mem.c and gambit.h files. Also I'm not 100% sure the technique is portable to architectures that don't provide byte-addressable memory (e.g. ARM - can somebody confirm this?).
That said, here's the code (hopefully somebody else will point out if I've gone wrong). The 'create-still-u8vector' ensures that the u8vector won't be moved by the garbage collector and reduces the refcount so that it'll be properly garbage collected. 'put-some-bytes-in-still-u8vector' shows how to convert the vector to an addressable array (e.g. for loading files into etc..).
Hope this helps!
Phil
(define create-still-u8vector (c-lambda (int) scheme-object #<<c-lambda-end ___result = ___alloc_scmobj(___sU8VECTOR, ___arg1, ___STILL); ___EXT(___release_scmobj) (___result); c-lambda-end ))
(define put-some-bytes-in-still-u8vector (c-lambda (scheme-object) void #<<c-lambda-end char *a; a = (char *)(___BODY_AS(___arg1,___tSUBTYPED)); a[0] = 'h'; a[1] = 'e'; a[2] = 'l'; a[3] = 'l'; a[4] = 'o'; c-lambda-end ))