Handling RPC requests

Let's connect dchatd up to JSON-RPC using DarkFi's rpc module.

We'll need to implement a trait called RequestHandler for our Dchat struct. RequestHandler is an async trait implementing a handler for incoming JSON-RPC requests. It exposes us to several methods automatically (including a pong response) but it also requires that we implement two methods: handle_request and connections_mut.

Let's start with handle_request. handle_request is simply a handle for processing incoming JSON-RPC requests that takes a JsonRequest and returns a JsonResult. JsonRequest is a JSON-RPC request object, and JsonResult is an enum that wraps around a given JSON-RPC object type. These types are defined inside jsonrpc.rs.

We'll use handle_request to run a match statement on JsonRequest.method.

Running a match on method will allow us to branch out to functions that respond to methods received over JSON-RPC. We haven't implemented any methods yet, so for now let's just return a JsonError.

impl RequestHandler for Dchat {
    async fn handle_request(&self, req: JsonRequest) -> JsonResult {
        if req.params.as_array().is_none() {
            return JsonError::new(ErrorCode::InvalidRequest, None, req.id).into()

        debug!(target: "RPC", "--> {}", serde_json::to_string(&req).unwrap());

        match req.method.as_str() {
            Some(_) | None => JsonError::new(ErrorCode::MethodNotFound, None, req.id).into(),