add example for rust-protobuf codec

[0xcaff]

Motivation

I've found the rust-protobuf crate to have some features which prost doesn't have (namely retaining unknown fields). I want to use tonic (codegen and all) with rust-protobuf as seamlessly as with prost.

Solution

This is an example of how I setup codgen and a codec to work as a drop in replacement for prost.

Looking for feedback

I'm looking for feedback about whether there's a better home for this glue to live. Should this be a first party feature in tonic instead of something in the examples folder? I considered putting it in its own crate but it didn't seem to generalize well. Should it go in rust-protobuf?

[djc]

I've found the rust-protobuf crate to have some features which prost doesn't have (namely retaining unknown fields).

Have you proposed this feature for implementation in prost? That seems like a simpler way forward.

Personally I'm not sure I'm motivated enough to review this code for inclusion in this repository (but other maintainers may have a different opinion).

[0xcaff]

I've found the rust-protobuf crate to have some features which prost doesn't have (namely retaining unknown fields).

Have you proposed this feature for implementation in prost? That seems like a simpler way forward.

Personally I'm not sure I'm motivated enough to review this code for inclusion in this repository (but other maintainers may have a different opinion).

The scope of adding unknown field support to prost is quite large. tokio-rs/prost#2 There's a big gap between proposing a feature in prost and having something which works today. Additionally I believe the design choices made by rust-protobuf vary quite a bit from prost and make sense for a lot of folks (look at the crate stats, I'm not the only user of rust-protobuf).

I understand that its not a priority. I will invest my effort elsewhere.