protobuf v4 codec and codegen

[kriswuollett]

Feature Request

Add protobuf v4 server code generation and server codec support.

Motivation

A beta version of the Google-assumed protobuf library seems to have been released (4.30.0-beta1). Assuming this will eventually provide semi-official Proto Text and JSON serialization support. See docs.

Given that the protobuf library wraps the C++ implementations, I'd lean towards assuming that any new gRPC Rust implementation will also wrap the C++ server given the battle-tested C++ proto messages stated reasonings. Or maybe it would be pure Rust, but based on another runtime like Cloudflare's Pingora. In any case, developers may wish to stick with tonic/hyper/tokio, but replace prost.

Caveats

• Message generation will probably not be done under the prost project?
• Have not tried to compile the protos myself personally (Ubuntu 22.04.5 LTS, x86_64):

$ sha256sum ~/tmp/bin/protoc 
1736d7bdcf94a2d96ed355c329b603f067dc70b3b7306431cedf5a3e5f2b91d8  /home/kris/tmp/bin/protoc
$ ~/tmp/bin/protoc --version
libprotoc 30.0
$ ~/tmp/bin/protoc --rust_out=./rust_out \
    --rust_opt=experimental-codegen=enabled \
    --rust_opt=kernel=cpp \
    -Iprotos protos/google/protobuf/source_context.proto
$ tree rust_out/
rust_out/
└── google
    └── protobuf
        ├── generated.rs
        ├── source_context.c.pb.rs
        └── source_context.pb.thunks.cc

3 directories, 3 files