How to test for supported functions?

[ximon18]

I recently created a PR for the Krill project to switch from the pkcs11 crate to the cryptoki crate and in doing so I discovered a difference: the pkcs11 crate requires lots of the pointers returned by C_GetFunctionList() to be non-null when the library is loaded, while cryptoki delays validation of function pointers until they are invoked.

If I want to verify as early as possible, and without actually invoking the functions, which functions a loaded library supports, how can I do that with cryptoki?

[ionut-arm]

Hey, apologies for the late reply!

Indeed, that's not available right now. I'm thinking that an option would be to have an enum with variants for all the PKCS11 functions and to use that in a call like check_if_fn_null, which returns an error if it is indeed null. Does that sound reasonable? Could start with a non-exhaustive list of methods in that enum.

[ximon18]

Sounds fine, with one question: if the fn is named "check" I would expect it to return a boolean, not an error. If it were instead named "require" I would expect it to return an error.

[ionut-arm]

Sure, or maybe a fn is_fn_null(...) -> bool. Do you have any preferences?

[ximon18]

I have a slight preference for testing for support rather than lack of support, and for keeping the term "null" out of the Rust API, though I'm not sure I can put forward strong arguments for either.