Allow use of loadbalanced RSocketRequester

See gh-498

spring-graphql/src/main/java/org/springframework/graphql/client/DefaultRSocketGraphQlClientBuilder.java

@@ -17,11 +17,15 @@
 package org.springframework.graphql.client;
 
 import java.net.URI;
+import java.util.List;
 import java.util.function.Consumer;
 
+import io.rsocket.loadbalance.LoadbalanceStrategy;
+import io.rsocket.loadbalance.LoadbalanceTarget;
 import io.rsocket.transport.ClientTransport;
 import io.rsocket.transport.netty.client.TcpClientTransport;
 import io.rsocket.transport.netty.client.WebsocketClientTransport;
+import org.reactivestreams.Publisher;
 import reactor.core.publisher.Mono;
 
 import org.springframework.lang.Nullable;
@@ -45,6 +49,10 @@ final class DefaultRSocketGraphQlClientBuilder
 
 	private final RSocketRequester.Builder requesterBuilder;
 
+	private Publisher<List<LoadbalanceTarget>> targetPublisher;
+
+	private LoadbalanceStrategy loadbalanceStrategy;
+
 	@Nullable
 	private ClientTransport clientTransport;
 
@@ -111,6 +119,13 @@ final class DefaultRSocketGraphQlClientBuilder
 		return this;
 	}
 
+	@Override
+	public DefaultRSocketGraphQlClientBuilder transports(Publisher<List<LoadbalanceTarget>> targetPublisher, LoadbalanceStrategy loadbalanceStrategy) {
+		this.targetPublisher = targetPublisher;
+		this.loadbalanceStrategy = loadbalanceStrategy;
+		return this;
+	}
+
 	@Override
 	public RSocketGraphQlClient build() {
 
@@ -120,13 +135,20 @@ final class DefaultRSocketGraphQlClientBuilder
 			builder.encoders(encoders -> setJsonEncoder(CodecDelegate.findJsonEncoder(encoders)));
 		});
 
-		Assert.state(this.clientTransport != null, "Neither WebSocket nor TCP networking configured");
-		RSocketRequester requester = this.requesterBuilder.transport(this.clientTransport);
+		RSocketRequester requester;
+
+		if (this.targetPublisher != null && this.loadbalanceStrategy != null) {
+			requester = this.requesterBuilder.transports(this.targetPublisher, this.loadbalanceStrategy);
+		} else {
+			Assert.state(this.clientTransport != null, "Neither WebSocket nor TCP networking configured");
+			requester = this.requesterBuilder.transport(this.clientTransport);
+		}
 		RSocketGraphQlTransport graphQlTransport = new RSocketGraphQlTransport(this.route, requester, getJsonDecoder());
 
 		return new DefaultRSocketGraphQlClient(
 				super.buildGraphQlClient(graphQlTransport), requester,
-				this.requesterBuilder, this.clientTransport, this.route, getBuilderInitializer());
+				this.requesterBuilder, this.clientTransport, this.targetPublisher, this.loadbalanceStrategy,
+				this.route, getBuilderInitializer());
 	}
 
 
@@ -141,19 +163,26 @@ final class DefaultRSocketGraphQlClientBuilder
 
 		private final ClientTransport clientTransport;
 
+		private final Publisher<List<LoadbalanceTarget>> targetPublisher;
+
+		private final LoadbalanceStrategy loadbalanceStrategy;
+
 		private final String route;
 
 		private final Consumer<AbstractGraphQlClientBuilder<?>> builderInitializer;
 
 		DefaultRSocketGraphQlClient(
 				GraphQlClient graphQlClient, RSocketRequester requester, RSocketRequester.Builder requesterBuilder,
-				ClientTransport clientTransport, String route, Consumer<AbstractGraphQlClientBuilder<?>> builderInitializer) {
+				ClientTransport clientTransport, Publisher<List<LoadbalanceTarget>> targetPublisher, LoadbalanceStrategy loadbalanceStrategy,
+				String route, Consumer<AbstractGraphQlClientBuilder<?>> builderInitializer) {
 
 			super(graphQlClient);
 
 			this.requester = requester;
 			this.requesterBuilder = requesterBuilder;
 			this.clientTransport = clientTransport;
+			this.targetPublisher = targetPublisher;
+			this.loadbalanceStrategy = loadbalanceStrategy;
 			this.route = route;
 			this.builderInitializer = builderInitializer;
 		}
@@ -174,6 +203,7 @@ final class DefaultRSocketGraphQlClientBuilder
 		public RSocketGraphQlClient.Builder<?> mutate() {
 			DefaultRSocketGraphQlClientBuilder builder = new DefaultRSocketGraphQlClientBuilder(this.requesterBuilder);
 			builder.clientTransport(this.clientTransport);
+			builder.transports(this.targetPublisher, this.loadbalanceStrategy);
 			builder.route(this.route);
 			this.builderInitializer.accept(builder);
 			return builder;

spring-graphql/src/main/java/org/springframework/graphql/client/RSocketGraphQlClient.java

@@ -17,10 +17,14 @@
 package org.springframework.graphql.client;
 
 import java.net.URI;
+import java.util.List;
 import java.util.function.Consumer;
 
 import io.rsocket.core.RSocketClient;
+import io.rsocket.loadbalance.LoadbalanceStrategy;
+import io.rsocket.loadbalance.LoadbalanceTarget;
 import io.rsocket.transport.ClientTransport;
+import org.reactivestreams.Publisher;
 import reactor.core.publisher.Mono;
 
 import org.springframework.messaging.rsocket.RSocketRequester;
@@ -129,6 +133,20 @@ public interface RSocketGraphQlClient extends GraphQlClient {
 		 */
 		B rsocketRequester(Consumer<RSocketRequester.Builder> requester);
 
+		/**
+		 * Build an {@link RSocketRequester} with an
+		 * {@link io.rsocket.loadbalance.LoadbalanceRSocketClient} that will
+		 * connect to one of the given targets selected through the given
+		 * {@link io.rsocket.loadbalance.LoadbalanceRSocketClient}.
+		 * @param targetPublisher a {@code Publisher} that supplies a list of
+		 * target transports to loadbalance against; the given list may be
+		 * periodically updated by the {@code Publisher}.
+		 * @param loadbalanceStrategy the strategy to use for selecting from
+		 * the list of loadbalance targets.
+		 * @return the same builder instance
+		 */
+		B transports(Publisher<List<LoadbalanceTarget>> targetPublisher, LoadbalanceStrategy loadbalanceStrategy);
+
 		/**
 		 * Build the {@code RSocketGraphQlClient} instance.
 		 */