1. zero-copy means bytes are always inlined in the raw message buffer, which means the app should always access bytes by a reference/pointer
2. You cannot compress the RPC message, if you want to fully leverage the advantages from zero serdes/copy
3. RC itself
To a very close approximation you can say that the official protobuf C++ library always copies and owns strings.
I have been on a similar odyssey making a 'zero copy' Java library that supports protobuf, parquet, thrift (compact) and (schema'd) json. It does allocate a long[] and break out the structure for O(1) access but doesn't create a big clump of object wrappers and strings and things; internally it just references a big pool buffer or the original byte[].
The speed demons use tail calls on rust and c++ to eat protobuf https://blog.reverberate.org/2021/04/21/musttail-efficient-i... at 2+GB/sec. In java I'm super pleased to be getting 4 cycles per touched byte and 500MB/sec.
Currently looking at how to merge a fast footer parser like this into the Apache Parquet Java project.
If this fixes that I might consider switching.
However, Google is also working in a new grpc-rust implementation and I have faith in them getting it right so holding tight a little bit longer.
I ended up building a protocol for my own use around a very strict subprocess boundary for Python (initially at least, protocol is meant to be universal). It has explicit payload shape, timeout and error semantics. I already went a little too far beyond my usecase with deterministic canonicalization for some common pitfall data types (I think pickle users would understand, though). It still needs some documentation polish, but if anyone would actually use it, I can document it properly and publish it.
Plain C structs that fit in a UDP datagram that you can reinterpret_cast from is still best. You can still provide schemas and UUIDs for that, and dynamically transcode to JSON or whatever.
For topics which are sending the state of something, a gap naturally self-recovers so long as you keep sending the state even if it doesn't change.
For message buses that need to be incremental, you need to have a separate snapshot system to recover state. That's usually pretty rare outside of things like order books (I work in low-latency trading).
For requests/response, I find it's better to tell the requester their request was not received rather than transparently re-send it, since by the time you re-send it it might be stale already. So what I do at the protocol level is just have ack logic, but no retransmit. Also it's datagram-oriented rather than byte-oriented, so overall much nicer guarantees than TCP (so long as all your messages fit in one UDP payload).
Didn't we learn this with python?
How many python http client libraries are in the dumping ground that is the python "batteries included" standard library?
And yet people always reach for the one that is outside stdlib.
It is not that everything should go into the stdlib, but having syn, procmacro and serde would be a good start imo. And like golang having a native http stack would be really awesome, every time you have to do any HTTP, you end up pulling in some c-based crypto lib, which can really mess up your day when you want to cross-compile. With golang it mostly just works.
It isn't really in the flavor of rust to do, so I don't think it is going to happen, but it is nice when building services, that you can avoid most dependencies.
Only when it falls short on my needs, I would drop the stdlib and go in dearch of a good quality, reputable, and reliable 3rd-party lib (which is easier said than done).
Has worked me well with Go and Python. I would enjoy the same with Rust. Or at a minimum, a list of libraries officialy curated and directly pointed at by the lang docs.
If anything, there should be “less than blessed” “*-awesome” libraries