femtopb-build

A code generator/protobuf compiler for the femtopb library. Uses protox and prost-build under the hood, but for now only a limited subset of their full APIs are exposed.

Usage

This library is meant to be used in your build.rs script to generate Rust code at build time. First, add both femtopb and femtopb-build to your dependencies like this:

[dependencies]

[build-dependencies]

An example of a valid build.rs file is:

fn main() -> anyhow::Result<()> {
    femtopb_build::compile_protos(
        &["src/myapi/v1/myapi.proto", "src/myapi/v1/foo.proto"],
        &["src"],
    )
}

The first argument to compile_protos lists which proto schema files to compile, and the second argument lists include dirs, where imports from one proto file to another will get resolved.

You may then include the parts of the schema that you want to use in your application. The file name of the generated file will be based on the protobuf package declaration (and for sanity should probably match your directory structure, too).

pub mod myapi {
    pub mod v1 {
        include!(concat!(env!("OUT_DIR"), "/myapi.v1.rs"));
    }
}

use myapi::v1::Foo;
// ...

To view the generated code, the easiest way is probably to just run cargo doc.

Checking in generated code

If you don't want to generate the code during the build, another common approach is to generate the code once and check in the generated code in source control. A common, but hacky, way is to add an example to your crate that generates the code.

For example, create a file called examples/mycrate-generate-schema.rs containing:

fn main() -> anyhow::Result<()> {
    femtopb_build::compile_protos_into(
        &["src/myapi/v1/myapi.proto", "src/myapi/v1/foo.proto"],
        &["src"],
        "src",
    )
}

Here, we use the compile_protos_into function that lets you specify a custom output directory, and we use the src dir of the crate to have the schemas live next to the rest of the application code (you may of course decide to structure things differently).