Add beacon_chain trait for gRPC server

beacon_node/rpc/src/beacon_chain.rs

@@ -0,0 +1,31 @@
+use beacon_chain::BeaconChain as RawBeaconChain;
+use beacon_chain::{
+    db::ClientDB,
+    fork_choice::ForkChoice,
+    parking_lot::RwLockReadGuard,
+    slot_clock::SlotClock,
+    types::{BeaconState, ChainSpec},
+    CheckPoint,
+};
+
+/// The RPC's API to the beacon chain.
+pub trait BeaconChain: Send + Sync {
+    fn get_spec(&self) -> &ChainSpec;
+
+    fn get_state(&self) -> RwLockReadGuard<BeaconState>;
+}
+
+impl<T, U, F> BeaconChain for RawBeaconChain<T, U, F>
+where
+    T: ClientDB + Sized,
+    U: SlotClock,
+    F: ForkChoice,
+{
+    fn get_spec(&self) -> &ChainSpec {
+        &self.spec
+    }
+
+    fn get_state(&self) -> RwLockReadGuard<BeaconState> {
+        self.state.read()
+    }
+}