You are adding more problems that don't exist to the specification.
As for strings, just shove a char[4096] in there. Use a bit of memory to save a lot of parsing.
D-Bus does in fact already have support for remoting, and like I said, you can tunnel it today. I'm only suggesting it because I have in fact tunneled D-Bus over the network to call into systemd specifically, already!
> As for strings, just shove a char[4096] in there. Use a bit of memory to save a lot of parsing.
OK. So... waste an entire page of memory for each string. And then we avoid all of that parsing, but the resulting code is horribly error-prone. And then it still doesn't work if you actually want really large strings, and it also doesn't do much to answer arrays of other things like structures.
Can you maybe see why this is compelling to virtually nobody?
For the love of God, use a proper slice/fat pointer, please.
Switching over to slices eliminates 90%+ of the issues with using C. Carrying around the base and the length eliminates a huge number of the overrun issues (especially if you don't store them consecutively).
Splitting the base and the offset gives a huge amount of semantic information and makes serialization vastly easier.
Correct as you may be though the argument here is that you should just write raw structs into Unix sockets. In this case you can't really use pointers. So, realistically, no slices either. In this context a fixed-size buffer is quite literally the only sensible thing you can do, but also, I think it's a great demonstration of why you absolutely shouldn't do this.
That said, if we're willing to get rid of the constraint of using only one plain C struct, you could use offsets instead of pointers. Allocate some contiguous chunk of memory for your entire request, place struct/strings/etc. in it, and use relative offsets. Then on the receiver side you just need some fairly basic validation checks to ensure none of the offsets go out of bounds. But at that point, you've basically invented part of Cap'n'proto, which begs the question... Why not just use something like that instead. It's pretty much the entire reason they were invented.
Oh well. Unfortunately the unforced errors of D-Bus seem like they will lead to an overcorrection in the other direction, turning the core of our operating system into something that I suspect nobody will love in the long term.
The only problem I have with Cap'n Proto is that the description is external to the serialization. Ideally I'd like the binary format to have a small description of what it is at the message head so that people can process messages from future versions.
ie. Something like: "Hmm, I recognize your MSG1 hash/UUID/descriptor so I can do a fast path and just map you directly into memory and grab field FD. Erm, I don't recognize MSG2, so I need to read the description and figure out if it even has field FD and then where FD is in the message."
It's better to design APIs to be extensible in ways that doesn't require dynamic introspection. It's always possible to have a "generic" header message that contains a more specific message inside of it, so that some consumers of an API can operate on messages even when they contain some data that they don't understand, but I think this still warrants some care to make sure it's definitely the right API design. Maybe in the future you'll come to the conclusion it would actually be better if consumers don't even try to process things they're not aware of as the semantics they implement may some day be wrong for a new type of message.
Versioning, at the least, is extremely difficult without this.
Look at the Vulkan API for an example of what they have to do in C to manage this. They have both an sType tag and a pNext extension pointer in order for past APIs to be able to consume future versions.
In general there's very little you can really do with a dynamic schema. Perhaps you can convert the message to JSON or something. But if your code doesn't understand the schema it received, then it can't possibly understand what the fields mean...