[zbhojkiuy]

I'm considering using the library for an embedded project that communicates with a Linux host and I have some questions.

- Does serialization/de-serialization require dynamic memory allocation? From what I've seen it looks like it doesn't.

- How are you handling endianness? floating point numbers?

- How complete/tested is the library? Are you aware of projects using it?

[arcticbull]

I suggest looking at nanopb to compare, that’s how I’ve solved this problem in the past. It’s just a couple kB on an AVR.

[zbhojkiuy]

I've used nanopb in the past. It's a great library. The only drawback is that it requires a type compilation step that generates the sources.

[coreytabaka]

Thanks for considering using libnop!

This library works well in an embedded context. I've personally used it on Cortex-M class micro controller firmware.

The serializer/deserializer does not require dynamic memory allocation. Whether or not dynamic allocation happens depends on how you use the library. If you avoid using data types that perform dynamic allocation (e.g. std::vector) and use (or write) Reader/Writer types that use static memory (e.g. nop::BufferReader/nop::BufferWriter) then you should be fine.

There are some nice tricks you can use to permit protocols that have convenient dynamic containers on the host and static versions on the embedded device:

https://github.com/google/libnop/blob/master/docs/getting-st... https://github.com/google/libnop/blob/master/docs/getting-st... https://github.com/google/libnop/blob/master/examples/shared...

Endianness is assumed to be little because the vast majority of hardware is little endian. There are utilities to convert here:

https://github.com/google/libnop/blob/master/include/nop/uti...

These are not currently used by the Reader and Writer types included with libnop for efficiency, but are available for you to use in your own Reader and Writer types if you really need it.

Floating point is a much stickier problem due to lack of standardization across hardware. The library does not address this automatically and just packs floating point types in machine order. However, the library provides tools to help address the issue. One approach that works well is to use a fixed point representation for the wire type -- a value wrapper type is convenient for automating this:

https://github.com/google/libnop/blob/master/docs/getting-st...

See the Fixed template in the example. This is especially handy if you have a micro controller without floating point support or you want to minimize the size of the payload at the cost of range and/or precision.

The library has a complete suite of tests and 97.9% line coverage according to GCOV, with particular attention to conditional and error paths.

We use the library for a few internal embedded prototypes. I have not tracked its usage outside of Google since its recent release.

Best, C

[kevincox]

> Endianness is assumed to be little because the vast majority of hardware is little endian ... libnop for efficiency

Do you have any evidence of this? I would be flabbergasted if a modern compiler couldn't optimize out a no-op endiannes conversion.

[coreytabaka]

For the most part the optimization works well. The more subtle issue is that the union trick used by the endian utilities is not compatible with constexpr expressions. There are some interesting use cases for constexpr serialization that fail if the conversions are interposed in the Reader/Writer types. The alternative is to use reinterpret_cast, which is also incompatible with constexpr expressions.

Moreover, endian conversion templates are unusually frustrating in the current C++ standard. I wish there were a better way, but one does not currently exist.

[zbhojkiuy]

Thanks for the detailed answer. Looks like it is a good fit for an embedded platform.

[coreytabaka]

Supporting embedded platforms is one of the objectives of the library. Feel free to open a ticket on github if you have any further questions.