Small improvement: Make from_c_parts only visible inside crate

[jjj-vtm]

Hi,

I made a (very) small PR to keep the from_c_parts private to the crate. The functions is very unsafe since it is possible to construct MQTTAsync_message from safe rust which will cause UB eg. set payload to point to unitialized memory.

Cheers,

Jan

[fpagliughi]

Hey! Thanks for the PR.

I'll have a look at it, but actually there is a big update that I'm about to drop in a branch to start reworking the library to totally hide the C dependencies as the first stage in moving toward a 100% Rust implementation.

The initial update will be to rework the options data structures. At the moment, they contain private FFI elements that are geared toward the C API, with internal cached data like CString values that are pinned to send to the C lib. These will be replaced by "normal" Rust data structures with public types that are String, u16, Duration, etc.

The existing data structs will remain to perform the actual FFI, but be crate-visible only.

Hopefully this will make things a little nicer.

[jjj-vtm]

That sounds great, looking forward to have a look at the branch. If the PR is so to speak included in the next release you can just close it. I was only wondering why from_c_parts was publicly exposed because it is very easy to cause UB from safe rust with this function.