private final Map<String, Supplier<Transport>> transportFactories = new HashMap<>();
    private final Map<String, Supplier<HttpServerTransport>> transportHttpFactories = new HashMap<>();
    private final List<TransportInterceptor> transportIntercetors = new ArrayList<>();

    /** Adds an http transport implementation that can be selected by setting {@link #HTTP_TYPE_KEY}. */
    // TODO: we need another name than "http transport"....so confusing with transportClient...
    private void registerHttpTransport(String key, Supplier<HttpServerTransport> factory) {
        if (transportClient) {
            throw new IllegalArgumentException("Cannot register http transport " + key + " for transport client");
        }
        if (transportHttpFactories.putIfAbsent(key, factory) != null) {
            throw new IllegalArgumentException("transport for name: " + key + " is already registered");
        }
    }
    /** Adds a transport implementation that can be selected by setting {@link #TRANSPORT_TYPE_KEY}. */
    private void registerTransport(String key, Supplier<Transport> factory) {
        if (transportFactories.putIfAbsent(key, factory) != null) {
            throw new IllegalArgumentException("transport for name: " + key + " is already registered");
        }
    }

    /**
     * Registers a new {@link TransportInterceptor}
     */
    private void registerTransportInterceptor(TransportInterceptor interceptor) {
        this.transportIntercetors.add(Objects.requireNonNull(interceptor, "interceptor must not be null"));
    }

// org.elasticsearch.plugins
/**
 * Plugin for extending network and transport related classes
 */
public interface NetworkPlugin {

    /**
     * Returns a list of {@link TransportInterceptor} instances that are used to intercept incoming and outgoing
     * transport (inter-node) requests. This must not return <code>null</code>
     *
     * @param namedWriteableRegistry registry of all named writeables registered
     * @param threadContext a {@link ThreadContext} of the current nodes or clients {@link ThreadPool} that can be used to set additional
     *                      headers in the interceptors
     */
    default List<TransportInterceptor> getTransportInterceptors(NamedWriteableRegistry namedWriteableRegistry,
                                                                ThreadContext threadContext) {
        return Collections.emptyList();
    }

    /**
     * Returns a map of {@link Transport} suppliers.
     * See {@link org.elasticsearch.common.network.NetworkModule#TRANSPORT_TYPE_KEY} to configure a specific implementation.
     */
    default Map<String, Supplier<Transport>> getTransports(Settings settings, ThreadPool threadPool, PageCacheRecycler pageCacheRecycler,
                                                           CircuitBreakerService circuitBreakerService,
                                                           NamedWriteableRegistry namedWriteableRegistry, NetworkService networkService) {
        return Collections.emptyMap();
    }

    /**
     * Returns a map of {@link HttpServerTransport} suppliers.
     * See {@link org.elasticsearch.common.network.NetworkModule#HTTP_TYPE_SETTING} to configure a specific implementation.
     */
    default Map<String, Supplier<HttpServerTransport>> getHttpTransports(Settings settings, ThreadPool threadPool, BigArrays bigArrays,
                                                                         PageCacheRecycler pageCacheRecycler,
                                                                         CircuitBreakerService circuitBreakerService,
                                                                         NamedXContentRegistry xContentRegistry,
                                                                         NetworkService networkService,
                                                                         HttpServerTransport.Dispatcher dispatcher,
                                                                         ClusterSettings clusterSettings) {
        return Collections.emptyMap();
    }
}