[plt-scheme] FFI - Implicit binding of _int to the correct _int32 or _int64

On Sep 26, Ray Racine wrote:
> 
> man hmac
>  #include <openssl/hmac.h>
> 
>         unsigned char *HMAC(const EVP_MD *evp_md, const void *key,
>                       int key_len, const unsigned char *d, int n,
>                       unsigned char *md, unsigned int *md_len);
> 
> Changing back to _int and using (_ptr o _int) the following is working
> for me.  Am I using (_ptr o _int) appropriately here?
> 
>   (define HMAC-SHA1/raw
>     (get-ffi-obj 'HMAC openssl-crypto
>                  (_fun [EVP_MD : _fpointer = (EVP_SHA1)]
>                        [key : _bytes]
>                        [key_len : _int = (bytes-length key)]
>                        [data : _bytes]
>                        [data_len : _int = (bytes-length data)]
>                        [md : _int = 0]
>                        [md_len : (_ptr o _int)]
>                        ->
>                        _pointer)))

This doesn't look right to me.  `md' should be a pointer, not an
integer, right?  Also, you're not using the resulting `md_len'.  (But
maybe you don't need to, if it returns the pointer too, and if it
points to a NUL-terminated string.)

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