added protos specification for Attester and created first draft for attestation_grpc_client (lighthouse-255)

validator_client/src/attester_service/attestation_grpc_client.rs

@@ -0,0 +1,32 @@
+use protos::services_grpc::AttestationServiceClient;
+use std::sync::Arc;
+
+use attester::{BeaconNode, BeaconNodeError, PublishOutcome};
+use types::{AttestationData, FreeAttestation, Slot};
+
+pub struct AttestationGrpcClient {
+    client: Arc<AttestationServiceClient>,
+}
+
+impl AttestationGrpcClient {
+    pub fn new(client: Arc<AttestationServiceClient>) -> Self {
+        Self { client }
+    }
+}
+
+impl BeaconNode for AttestationGrpcClient {
+    fn produce_attestation_data(
+        &self,
+        slot: Slot,
+        shard: u64,
+    ) -> Result<Option<AttestationData>, BeaconNodeError> {
+        Err(BeaconNodeError::DecodeFailure)
+    }
+
+    fn publish_attestation_data(
+        &self,
+        free_attestation: FreeAttestation,
+    ) -> Result<PublishOutcome, BeaconNodeError> {
+        Err(BeaconNodeError::DecodeFailure)
+    }
+}