no_std support?

[vitiral]

I didn't see no_std support in the documentation / cargo.toml / issues so I thought I would open one. This library seems perfect for no_std serialization in microcontrollers. What are the biggest barriers to supporting no_std? Would you welcome a PR that did so?

Thanks!

[dtolnay]

Yes! I don't know what the biggest barriers are but we would love a PR to support no_std.

[vitiral]

A rough design could be:

• have std feature for current functionality, and default-features = false mean no_std
• when not feature=std:
  • don't use anything from the io or collections/vecmodules (std only), instead use array references like the byteorder crate
  • errors/expect/etc shouldn't use strings (or use very short ones) to stay as memory efficient as possible.
• use default-features = false on serde along with the conditional cargo feature (rust-lang/cargo#633)

Theoretically I hope that's it! Not a small amount of work, but hopefully doable

[vitiral]

I'm going to try and give this a shot this week

[vitiral]

It looks like we depend on rust-num/num#296, which is an open PR that will hopefully be done soonish!

[vks]

rust-num/num#296 has been merged, num-traits 0.1.38 can be build without std.

[vitiral]

I took an initial stab at this and it is way more difficult than I first anticipated.

Also, ssmarshall does pretty much everything I needed

https://crates.io/crates/ssmarshal

Not sure where this issue should go, but I won't be working on it!

[vitiral]

Thus crate could be no_std, but it would basically be ssmarshall with u32 enum variants and configurable byte ordering

[TyOverby]

Yeah... bincode is pretty dependent on std::io::Write and std::io::Read which isn't no_std compatible.

[astraw]

core_io's documentation says that it provides the Read and Write traits for use with core and does not require std. I have not tried it myself.

[vlad9486]

Take a look on my crate tirse. I just committed, the work still in progress.

[noonien]

Any update on this?

[vks]

I think no_std support is not intended for bincode. Such support would likely require significant limitations, see the ssmarshall crate, which is essentially a reimagination of bincode for no_std applications.

[noonien]

The no_std story has really changed since 2 years ago. It's a lot easier to provide no_std support nowadays.

[vitiral]

some context: there IS a protobuf implementation (in C) for micro-controllers:
https://github.com/nanopb/nanopb