Overview

This template contains a reference implementation of how to implement a rust binary that can be consumed by HashiCorp's go-plugin.

Current limitations

This project template was extracted from the nomad-driver-wasm project and refactored to conform with the KV example used in the go-plugin repository. It currently, only implements the server side of the plugin, since Nomad itself runs the client process in the project this derived from. Work is currently under way to implement a client process written in Rust, and when finished, will be submitted for consideration as an official example in the go-plugin repository.

Usage

Review the references implementation contained in main.rs to get an understanding of what you will be doing in your own repository. Ultimately, you will replace this code, but it is there to help you get your bearings.
Create a new repository from this template.
Locate the .proto files you intend to use
Optionally, copy the .proto files to the proto directory
Remove the kv.proto file
Review and modify the build.rs file

fn main() -> Result<()> {
  tonic_build::configure()
  .build_server(true)
  .out_dir("src/proto")
  .compile_well_known_types(true)
  .include_file("mod.rs")
  .type_attribute(".", "#[derive(serde::Deserialize)]")
  .type_attribute(".", "#[derive(serde::Serialize)]")
  .compile(&["proto/kv.proto"], &["proto"])
  .unwrap();

  Ok(())
}

Build Settings of interest

out_dir - This is the directory where tonic_build and prost will output generated code. You can rename this directory if you like. Be mindful that if you do, you will need to update all example Rust code to reflect the new module structure.
include_file - This instructs prost to sort out include paths for any .proto files you add that reference each other. This is highly recommended, though you can do this manually.
compile_well_known_types - tells prost to generate output for well-known google protobuf types. This is optional, but I've found it helpful.
type_attribute - This adds the specified derive directive to structs generated by prost.
.compile - Takes two arguments.
- The first is the set of .proto files to generate code for. If you do not want to replicate your files to the proto folder, you can delete it, and use relative paths here.
- The second is the set of directories to use as search roots when trying to resolve .proto dependencies referenced within the targeted .proto files. These can also be relative paths.

Generating code

Update the Cargo.toml file to match your desired package/bin names
Run cargo build --bin <your-package-name>
This will fail, because the reference implementation is still in place.
Once it fails, look in the out_dir and you should see two or more files
- mod.rs - This is the module file that contains all necessary includes. You should reference this file to understand the namespace hierarch of your generated code.
- *.proto.rs - These file will contain your generated code. You should have one per proto.rs file you included as a compile argument. You may also have a google.protobuf.rs file if you kept the compile_well_known_types settings from the example.

Implementing Services

Review the generated proto/*.proto.rs files you generated, and look for any structs named <TypeName>Server. For example, the reference implementation includes the following code.

pub trait Kv: Send + Sync + 'static {
    async fn get(
        &self,
        request: tonic::Request<super::GetRequest>,
    ) -> Result<tonic::Response<super::GetResponse>, tonic::Status>;
    async fn put(
        &self,
        request: tonic::Request<super::PutRequest>,
    ) -> Result<tonic::Response<super::Empty>, tonic::Status>;
}
#[derive(Debug)]
pub struct KvServer<T: Kv> {
    inner: _Inner<T>,
    accept_compression_encodings: (),
    send_compression_encodings: (),
}

Each service you have defined in your .proto files should have a corresponding server entry like this. Notice also, that there is a trait associated with the KvServer struct. Tonic will generate a great deal of the GRPC plumbing code for you, but you will need to implement the trait functions that contain your service logic.

Here is the Kv trait implementation from the current main.rs for example.

#[tonic::async_trait]
impl Kv for PluginServer {
    async fn get(&self, request: Request<GetRequest>) -> Result<Response<GetResponse>, Status> {
        let key = request.get_ref().clone().key;
        if key.is_empty() {
            return Err(Status::invalid_argument("key not specified"));
        }

        let store_clone = Arc::clone(&self.store);
        let store = store_clone.lock().unwrap();

        match store.get(&key) {
            Some(value) => Ok(Response::new(GetResponse {
                value: value.clone().to_vec(),
            })),
            None => Err(Status::invalid_argument("key not found")),
        }
    }

    async fn put(&self, request: Request<PutRequest>) -> Result<Response<Empty>, Status> {
        let request_ref = request.get_ref().clone();
        if request_ref.key.is_empty() {
            return Err(Status::invalid_argument("key not specified"));
        }

        let store_clone = Arc::clone(&self.store);
        let mut store = store_clone.lock().unwrap();

        store.insert(request_ref.key, request_ref.value);

        Ok(Response::new(Empty {}))
    }
}

Testing

To test the reference implementation, open two terminals at the root of this directory.

In one run:

RUST_LOG=debug cargo run --bin go-plugin-rs
   Compiling go-plugin-rs v0.1.0 (/Users/derekstrickland/goland/go-plugin-rs)
    Finished dev [unoptimized + debuginfo] target(s) in 4.61s
     Running `target/debug/go-plugin-rs`
1|2|tcp|127.0.0.1:5001|grpc

Notice the 1|2|tcp|... line. go-plugin requires this to be written to satisfy its handshake protocol.

In the other run:

$ RUST_LOG=debug cargo run --bin test-client
   Compiling go-plugin-rs v0.1.0 (/Users/derekstrickland/goland/go-plugin-rs)
    Finished dev [unoptimized + debuginfo] target(s) in 3.57s
     Running `target/debug/test-client`
[2021-10-19T11:03:00Z DEBUG hyper::client::connect::http] connecting to 0.0.0.0:5001 
......
[2021-10-19T11:03:00Z INFO  test_client] get response: bar

Further examples

Review the rest of the main.rs file, as well as the tonic examples to see how to configure a basic server.

When you are ready, start implementing your own services! The example in this repository is very simple. For additional examples, including how to work with streaming endpoints, see the nomad-driver-wasm repository.

DerekStrickland/go-plugin-rs