[comprehensive] Resource types for gRPC client and server.

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.

Client Usage

Define a struct containing a [tonic] client wrapped around a channel and derive [GrpcClient] on it. This will become a [comprehensive::v1::Resource] that can be depended upon. Call .client() to get a (cheap) clone of the gRPC client.

use comprehensive_grpc::GrpcClient;
use comprehensive_grpc::client::Channel;

#[derive(GrpcClient)]
struct MyClientResource(
    pb::test_client::TestClient<Channel>,
);

struct OtherResourceThatConsumesClient {
    the_client: std::sync::Arc<MyClientResource>,
}

impl OtherResourceThatConsumesClient {
    async fn something(&self) {
        let mut tonic_client = self.the_client.client();
        println!("{:?}", tonic_client.greet(()).await);
    }
}

Server Usage

Derive resources that conjure the server and install themselves in it:

Any Resource that implements [GrpcService] and exports itself as a trait resource for dyn GrpcService will be picked up automatically by the server and served.

The #[export_grpc] attribute argument to the [comprehensive::v1::resource] macro is a shortcut for #[export(dyn GrpcService)] and also implementing the [GrpcService] trait.

use comprehensive::{NoArgs, NoDependencies, ResourceDependencies};
use comprehensive::v1::{AssemblyRuntime, Resource, resource};
use comprehensive_grpc::GrpcService;

#[resource]
#[export_grpc(pb::test_server::TestServer)]
#[proto_descriptor(pb::FILE_DESCRIPTOR_SET)]
impl Resource for TestService {
    fn new(
        _: NoDependencies, _: NoArgs, _: &mut AssemblyRuntime<'_>
    ) -> Result<Arc<Self>, std::convert::Infallible> {
        Ok(Arc::new(Self {}))
    }
}

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

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

Command line flags for the gRPC client

Each flag is prefixed with the name of the resource that it belongs to, converted to kebab case (struct VerySpecialClient → --very-special-client-). See [warm_channels::grpc_channel] and [warm_channels::grpc::GRPCChannelConfig] for details on most parameters.

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");