Certainly, but for instance, take one of your examples: Kaitai Struct. It doesn't have support for C (at least it's not listed among the languages on its homepa

Certainly, but for instance, take one of your examples: Kaitai Struct. It doesn't have support for C (at least it's not listed among the languages on its homepage). OTOH, for more complex payloads I've often seen Protocol Buffers used (yes, I know they don't have native C support either but there's lots of good libraries for using `protobuf`s with C). The thing with FFIs is that above all we want them to be fast and simple. C rules for laying out structs generally means no parsing necessary, with direct access to fixed offsets for everything you want. If you're ever having problems figuring out the layout of a struct, it's relatively straightforward to just dump some simple load/store code into a compiler and have a look at what it does (assuming you can understand assembly at a basic level): https://godbolt.org/g/khGPWA https://godbolt.org/g/khGPWA