- Store EVP_MD_CTX in a separate struct.
- Add with_context() constructor that uses an existing context.
- Switch to EVP_Digest(Init|Final)_ex for efficient context reuse.
- Make update() borrow &mut self.
- Make finalize() consume self. Add finalize_reuse() that also returns the
context which can be passed to from_context() constructor for reuse.
These changes let the type system prevent illegal calls to update() and
finalize().
CRYPTO_free() ends up being used for a variety of types of data, not just
c_char. And it essentially takes full ownership of the type, making
*mut appropriate.
With this change it also more closely (exactly) matches the C defintion:
void CRYPTO_free(void *ptr);
Chris Cole