no_std

[nickray]

Hiya, any plans for no_std compatibility? I'm looking for a DER writer in the context of FIDO2 authenticators (on microcontrollers), and this seems the most minimal implementation I've found.

There are two issues:

• lack of core::io::Writer (but there's e.g. core_io)
• lack of Vec and friends (but there's heapless)

Possibly having a default-feature std would go against the "minimal" intent of this library. My alternative plan is to fork this into derpy and do things there.

[heartsucker]

I don't have plans for that at the moment, but that is entirely because I threw this crate together to have something minimal for other work I was doing. That said, I think that should be doable, and it would also force me to clean up the API some since it's not super ergonomic. Is this something you could possible help with?

[nickray]

Maybe! 😊 Although not likely soon, it turns out all I needed is formatting a sequence of two integers: https://github.com/nickray/usbd-ctaphid/blob/main/src/insecure.rs#L105-L147.

I will revisit when I move from "make it work" to "make it right".

[heartsucker]

I'll see if I can get this done if a few hours. If so, I can close this. Otherwise, I'll have to get to it another time.

[nickray]

I did some work in https://github.com/nickray/usbd-ctaphid/blob/e1c02114d1c816d5b65770e70b84790ea677b45d/src/derpy.rs, covers my use case of sequences of integers for ASN.1 DER formatting of ECDSA signatures. I'm not sure this merits inclusion here (apart from being written a bit more understandably), mainly because there's no real i.e. agreed-upon equivalent for Write in no_std.

[heartsucker]

I think what may be reasonable is tidying up the current API and then adding a no_std features that disables all the heap things and leaves only the stack-only things. Because I agree that some of your use cases apply to others, and I think the minimal nature of this crate makes inclusion natural.