Add validator_node, restructure binaries, gRPC.

This is a massive commit which restructures the workspace, adds a very
basic, untested, validator client and some very basic, non-functioning
gRPC endpoints to the beacon-node.

beacon_node/src/rpc/mod.rs

@@ -0,0 +1,79 @@
+use std::sync::Arc;
+
+use futures::Future;
+use grpcio::{Environment, RpcContext, Server, ServerBuilder, UnarySink};
+
+use protos::services::{
+    BeaconBlock as BeaconBlockProto, ProduceBeaconBlockRequest, ProduceBeaconBlockResponse,
+    PublishBeaconBlockRequest, PublishBeaconBlockResponse,
+};
+use protos::services_grpc::{create_beacon_block_service, BeaconBlockService};
+
+use slog::{info, Logger};
+
+#[derive(Clone)]
+struct BeaconBlockServiceInstance {
+    log: Logger,
+}
+
+impl BeaconBlockService for BeaconBlockServiceInstance {
+    /// Produce a `BeaconBlock` for signing by a validator.
+    fn produce_beacon_block(
+        &mut self,
+        ctx: RpcContext,
+        req: ProduceBeaconBlockRequest,
+        sink: UnarySink<ProduceBeaconBlockResponse>,
+    ) {
+        println!("producing at slot {}", req.get_slot());
+
+        // TODO: build a legit block.
+        let mut block = BeaconBlockProto::new();
+        block.set_slot(req.get_slot());
+        block.set_block_root("cats".as_bytes().to_vec());
+
+        let mut resp = ProduceBeaconBlockResponse::new();
+        resp.set_block(block);
+
+        let f = sink
+            .success(resp)
+            .map_err(move |e| println!("failed to reply {:?}: {:?}", req, e));
+        ctx.spawn(f)
+    }
+
+    /// Accept some fully-formed `BeaconBlock`, process and publish it.
+    fn publish_beacon_block(
+        &mut self,
+        ctx: RpcContext,
+        req: PublishBeaconBlockRequest,
+        sink: UnarySink<PublishBeaconBlockResponse>,
+    ) {
+        println!("publishing {:?}", req.get_block());
+
+        // TODO: actually process the block.
+        let mut resp = PublishBeaconBlockResponse::new();
+        resp.set_success(true);
+
+        let f = sink
+            .success(resp)
+            .map_err(move |e| println!("failed to reply {:?}: {:?}", req, e));
+        ctx.spawn(f)
+    }
+}
+
+pub fn start_server(log: Logger) -> Server {
+    let log_clone = log.clone();
+
+    let env = Arc::new(Environment::new(1));
+    let instance = BeaconBlockServiceInstance { log };
+    let service = create_beacon_block_service(instance);
+    let mut server = ServerBuilder::new(env)
+        .register_service(service)
+        .bind("127.0.0.1", 50_051)
+        .build()
+        .unwrap();
+    server.start();
+    for &(ref host, port) in server.bind_addrs() {
+        info!(log_clone, "gRPC listening on {}:{}", host, port);
+    }
+    server
+}