Construct Pkcs11 from cryptoki_sys::Pkcs11

[robin-nitrokey]

Hi! I’d like to use cryptoki to test a PKCS11 module that is written in Rust. As far as I see, I currently have to compile the module to a binary and then load it with cryptoki::context::Pkcs11::new. Internally, this function constructs a cryptoki_sys::Pkcs11 instance from the loaded library and passes it to cryptoki::context::Pkcs11::_new. I think I should be able to construct the cryptoki_sys::Pkcs11 directly using function pointers to the Rust implementation, avoiding the additional compilation step. Would you accept a PR to make Pkcs11::_new part of the public API, maybe as Pkcs11::new_from_sys or Pkcs11::new_from_raw?

[hug-dev]

Hello! Interesting use-case! This sounds like it would facilitate testing.

I guess even if we make Pkcs11::_new public, you would need another constructor for cryptoki_sys::Pkcs11 since the libloading field is not public? I guess if we make all those new methods unsafe that could work!

Will this be useful outside of testing scenarios though? It's always a bit delicate to add public APIs that are only used for testing 😁
I was thinking of two other ideas to explore as well:

1. Could the new_from_self method help you simplifying the testing process in any way? By baking in your PKCS11 module into the executable somehow to avoid double compilation
2. Could that be generalized to support static linking to a PKCS11 implementation? Maybe as a new (non-default) feature. That was an idea to solve this too

[robin-nitrokey]

Oh, you are right, I missed that cryptoki_sys::Pkcs11 has this private field. I’ll try to use new_from_self and report back.

[Jakuje]

This could also be helpful for us in kryoptic as we had to write some hacks to make the testing through rust-cryptoki working as we needed to emit the .so pkcs11 module first before running the tests which is not straight-forward. Though if we take this shortcut, we are testing the internals, of the pkcs11 module and not the pkcs11 module interface and the API that will be visible and used by the end users. So both of the ways have some downsides.