merfolk

merfolk is a minimal extensible remote procedure call framework.

The architecture is split into three modular parts: the Backend, the Frontend and optional Middlewares.

merfolk is a collection of parts. The main part is Mer the orchestrator type and a collection of Backends, the Frontends and Middlewares (the Folk).

Mer can act as a server or a client or both depending on the configuration.

Backend

The Backend is responsible for sending and receiving RPCs. Depending on the Backend this can happen over different channels (e.g. http, serial port, etc.). The Backend serializes and deserializes the RPCs using the [serde] framework.

Frontend

The Frontend is providing an API to make RPCs and to receive them. The way RPCs are made by the client and and handled the server depend on the frontend Frontend

Middleware

A Middleware can modify sent and received RPCs and replies. Or perform custom actions on a sent or received RPC and reply.

Use Mer

Mer needs a Backend and a Frontend to operate. The following examples uses the Http Backend and the Register and Derive Frontend (see their documentation on how to use them).

How to use Mer (how to setup the server and client) depends strongly on the used Frontend.

Server

// remote procedure definitions
fn add(a: i32, b: i32) -> i32 {
  a + b
}
fn subtract(a: i32, b: i32) -> i32 {
  a - b
}

// build the backend
let backend = Http::builder()
  // configure backend as server
  .listen(SocketAddr::new(IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1)), 8080))
  .build()
  .unwrap();

// build the frontend
let frontend = Register::builder()
  .procedures(
    vec![
      ("add", Register::<Http>::make_procedure(|(a, b)| add(a, b))),
      ("subtract", Register::<Http>::make_procedure(|(a, b)| subtract(a, b))),
    ]
    .into_iter()
    .collect(),
  )
  .build()
  .unwrap();

// register the procedures in the frontend
frontend.register("add", |(a, b)| add(a, b)).unwrap();
frontend.register("subtract", |(a, b)| subtract(a, b)).unwrap();

// build merfolk instance acting as server
let _merfolk = Mer::builder().backend(backend).frontend(frontend).build().unwrap();

Client

// build the backend
let backend = Http::builder()
  // configure backend as client
  .speak("http://localhost:8080".parse::<hyper::Uri>().unwrap())
  .build()
  .unwrap();

// build the frontend
let frontend = Register::builder().build().unwrap();

// build merfolk instance acting as client
let merfolk = Mer::builder().backend(backend).frontend(frontend).build().unwrap();

// call remote procedures via the frontend
let result_add: Result<i32> = merfolk.frontend(|f| f.call("add", &(1, 2))).unwrap();
let result_subtract: Result<i32> = merfolk.frontend(|f| f.call("subtract", &(1, 2))).unwrap();

Advanced

// remote procedure definitions for server
#[frontend()]
struct Receiver {}

#[frontend(target = "Receiver")]
trait Definition {
  fn some_function(arg: String) {}
}

// build the backend
let backend = Http::builder()
  // configure backend as client
  .speak("http://localhost:8080".parse::<hyper::Uri>().unwrap())
  // configure backend as server
  .listen(SocketAddr::new(IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1)), 8081))
  .build()
  .unwrap();

// build the client frontend
let caller_frontend = Register::builder().build().unwrap();

// build the server frontend
let receiver_frontend = Receiver::builder().build().unwrap();

// combine the frontends using the [`Duplex`](/merfolk_frontend_derive) frontend
let frontend = Duplex::builder().caller(caller_frontend).receiver(receiver_frontend).build().unwrap();

// build router middleware
let middleware = Router::builder().routes(vec![("prefix_(.*)".to_string(), "$1".to_string())]).build_boxed().unwrap();

// build merfolk instance acting as client and server
let merfolk = Mer::builder().backend(backend).frontend(frontend).middlewares(vec![middleware]).build().unwrap();

// call remote procedures via the caller frontend
let result: String = merfolk.frontend(|f| f.caller.call("some_remote_function", &()).unwrap()).unwrap();

Provided Modules

Develop a Module for Mer (called a Folk)

If communication over a specific channel or a different frontend etc. is needed a module can be created by implementing the Backend, Frontend or Middleware trait.

For examples please see the provided modules