How to share *.proto files with other repositories

[torao]

Summary

Ostracon's API request/response is defined in ProtocolBuffers *.proto files, and we need to discuss how the *.proto files should be shared when creating another application related to Ostracon.

Problem Definition

The current *.proto file is located in the same place as the regular Ostracon source files. Eath related-applications will have to copy the *.proto file when developing them, which isn't easy to maintain and may cause version differences.

Proposal

One solution is to create an independent repository that defines the schema of the inter-system interfaces, such as ProtocolBuffers, and have each project, including Ostracon, reference that repository (e.g., as a submodule).

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[torao]

Currently-known issues for sharing ProtocolBuffers definitions with other languages:

1. A lot of *.proto files contains gogoproto-specific import "gogoproto/goto.proto" and attribute such as [(gogoproto.nullable) = false] or (gogoproto.customname) = "ID"].
2. There is no way to specify a Rust mod name (values like option rust_module cannot specify). As a result, types/types.proto and privval/types.proto are output to the same file types.rs.

[torao]

There are two possible schemas for creating client projects that use ProtocolBuffers to communicate with Ostracon.

1. each project must copy and use the *.proto files from http://github.com/line/ostracon (better to copy from github at build time).
2. separate the *.proto files currently stored in the Ostracon repository into an independent repo, and each project will refer to that one. Optionally it's better to create a library for each language (e.g. libXXX.a for C, crate for Rust, etc.).

Currently, the only projects that need to share *.proto are internal attempts, so I think schema 1 is fine. If more projects connect to Ostracon in the future, we can do 2.

We will leave this issue for the future use of *.proto files by multiple projects.