[comprehensive] [Resource] types for gRPC serving

This crate provides [Resource] types for use in a [comprehensive] Assembly. To use it, build an Assembly and include resources from this crate in the dependency graph.

Usage

There are 2 ways to use it:

Derive resources that conjure the server and install themselves in it

A [GrpcService] is a [Resource] and depending upon it will cause the server to run with the service in question (and others) installed:

use comprehensive::{NoArgs, NoDependencies, Resource, ResourceDependencies};
use comprehensive_grpc::GrpcService;

impl Resource for Implementation {
    type Args = NoArgs;
    type Dependencies = NoDependencies;
    const NAME: &str = "TestServer";

    fn new(_: NoDependencies, _: NoArgs) -> Result<Self, Box<dyn std::error::Error>> {
        Ok(Self {})
    }
}

#[tonic::async_trait]
impl pb::test_server::Test for Implementation {
    // ...
}

#[derive(GrpcService)]
#[implementation(Implementation)]
#[service(pb::test_server::TestServer)]
#[descriptor(pb::FILE_DESCRIPTOR_SET)]
struct TestService;

#[derive(ResourceDependencies)]
struct AutoServer {
    _s: std::sync::Arc<TestService>,
}
let assembly = comprehensive::Assembly::<AutoServer>::new().unwrap();

Depend on [GrpcServer] directly

The server can bee configured to add gRPC services to it:

use comprehensive::ResourceDependencies;
use comprehensive_grpc::GrpcServer;

#[derive(ResourceDependencies)]
struct JustAServer {
    server: std::sync::Arc<GrpcServer>,
}

let assembly = comprehensive::Assembly::<JustAServer>::new().unwrap();
assembly.top.server.register_encoded_file_descriptor_set(
    pb::FILE_DESCRIPTOR_SET
);
assembly.top.server.add_service(
    pb::test_server::TestServer::new(Implementation{})
);

Command line flags for the gRPC server

On descriptors

Because gRPC server reflection is very useful for diagnostics yet it is too easy to forget to install the descriptors needed to make it happen, [comprehensive_grpc] tries to insist that descriptors are installed before services are added to the server.

To obtain file descriptors, put this in build.rs:

let fds_path =
    std::path::PathBuf::from(std::env::var("OUT_DIR").expect("$OUT_DIR")).join("fdset.bin");
tonic_build::configure()
    .file_descriptor_set_path(fds_path)

And this where you include your protos:

pub(crate) const FILE_DESCRIPTOR_SET: &[u8] = tonic::include_file_descriptor_set!("fdset");