Discover RPC NOT_FOUND result tweaks (#154)

* Discover RPC returns OK when there's an empty list

* Discover RPC returns NOT_FOUND for unimplemented categories

Author: jeffyanta

ocp/rpc/currency/discovery.go

@@ -42,21 +42,23 @@ func (s *currencyServer) Discover(req *currencypb.DiscoverRequest, stream curren
 			return time.Since(record.CreatedAt) < newDiscoveredCurrenciesAgeLimit
 		}
 	default:
-		return status.Error(codes.InvalidArgument, "invalid category")
+		return stream.Send(&currencypb.DiscoverResponse{
+			Result: currencypb.DiscoverResponse_NOT_FOUND,
+		})
 	}
 
 	metadataRecords, err := s.mintDataProvider.GetAllCachedCurrencyMetadata(ctx)
 	if err == currency.ErrNotFound {
 		return stream.Send(&currencypb.DiscoverResponse{
-			Result: currencypb.DiscoverResponse_NOT_FOUND,
+			Result: currencypb.DiscoverResponse_OK,
 		})
 	} else if err != nil {
 		log.With(zap.Error(err)).Warn("failure getting currency metadata records")
 		return status.Error(codes.Internal, "")
 	}
 	if len(metadataRecords) == 0 {
 		return stream.Send(&currencypb.DiscoverResponse{
-			Result: currencypb.DiscoverResponse_NOT_FOUND,
+			Result: currencypb.DiscoverResponse_OK,
 		})
 	}
 
@@ -106,7 +108,7 @@ func (s *currencyServer) Discover(req *currencypb.DiscoverRequest, stream curren
 
 	if len(candidates) == 0 {
 		return stream.Send(&currencypb.DiscoverResponse{
-			Result: currencypb.DiscoverResponse_NOT_FOUND,
+			Result: currencypb.DiscoverResponse_OK,
 		})
 	}
 
@@ -137,12 +139,6 @@ func (s *currencyServer) Discover(req *currencypb.DiscoverRequest, stream curren
 		protoMints = append(protoMints, protoMint)
 	}
 
-	if len(protoMints) == 0 {
-		return stream.Send(&currencypb.DiscoverResponse{
-			Result: currencypb.DiscoverResponse_NOT_FOUND,
-		})
-	}
-
 	return stream.Send(&currencypb.DiscoverResponse{
 		Result: currencypb.DiscoverResponse_OK,
 		Mints:  protoMints,