Support for LoadbalanceRSocketClient

Closes gh-25333

Author: rstoyanchev

spring-messaging/src/main/java/org/springframework/messaging/rsocket/DefaultRSocketRequesterBuilder.java

@@ -28,11 +28,15 @@
 import io.rsocket.core.RSocketClient;
 import io.rsocket.core.RSocketConnector;
 import io.rsocket.frame.decoder.PayloadDecoder;
+import io.rsocket.loadbalance.LoadbalanceRSocketClient;
+import io.rsocket.loadbalance.LoadbalanceStrategy;
+import io.rsocket.loadbalance.LoadbalanceTarget;
 import io.rsocket.metadata.WellKnownMimeType;
 import io.rsocket.transport.ClientTransport;
 import io.rsocket.transport.netty.client.TcpClientTransport;
 import io.rsocket.transport.netty.client.WebsocketClientTransport;
 import io.rsocket.util.DefaultPayload;
+import org.reactivestreams.Publisher;
 import reactor.core.publisher.Mono;
 
 import org.springframework.core.ReactiveAdapter;
@@ -171,6 +175,25 @@ public RSocketRequester transport(ClientTransport transport) {
 		return new DefaultRSocketRequester(client, null, dataMimeType, metaMimeType, strategies);
 	}
 
+	@Override
+	public RSocketRequester transports(
+			Publisher<List<LoadbalanceTarget>> targetPublisher, LoadbalanceStrategy loadbalanceStrategy) {
+
+		RSocketStrategies strategies = getRSocketStrategies();
+		MimeType metaMimeType = getMetadataMimeType();
+		MimeType dataMimeType = getDataMimeType(strategies);
+
+		RSocketConnector connector = initConnector(
+				this.rsocketConnectorConfigurers, metaMimeType, dataMimeType, strategies);
+
+		LoadbalanceRSocketClient client = LoadbalanceRSocketClient.builder(targetPublisher)
+				.connector(connector)
+				.loadbalanceStrategy(loadbalanceStrategy)
+				.build();
+
+		return new DefaultRSocketRequester(client, null, dataMimeType, metaMimeType, strategies);
+	}
+
 	@Override
 	@SuppressWarnings("deprecation")
 	public Mono<RSocketRequester> connectTcp(String host, int port) {

spring-messaging/src/main/java/org/springframework/messaging/rsocket/RSocketRequester.java

@@ -17,12 +17,15 @@
 package org.springframework.messaging.rsocket;
 
 import java.net.URI;
+import java.util.List;
 import java.util.function.Consumer;
 
 import io.rsocket.ConnectionSetupPayload;
 import io.rsocket.Payload;
 import io.rsocket.RSocket;
 import io.rsocket.core.RSocketClient;
+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;
@@ -116,8 +119,9 @@ static RSocketRequester.Builder builder() {
 	}
 
 	/**
-	 * Wrap an existing {@link RSocket}. Typically used in client or server
-	 * responders to wrap the {@code RSocket} for the remote side.
+	 * Wrap an existing {@link RSocket}. Typically for internal framework use,
+	 * to wrap the remote {@code RSocket} in a client or server responder, but
+	 * it can also be used to wrap any {@link RSocket}.
 	 */
 	static RSocketRequester wrap(
 			RSocket rsocket, MimeType dataMimeType, MimeType metadataMimeType,
@@ -224,36 +228,56 @@ interface Builder {
 		RSocketRequester.Builder apply(Consumer<RSocketRequester.Builder> configurer);
 
 		/**
-		 * Build an {@link RSocketRequester} instance for use with a TCP
-		 * transport. Requests are made via {@link io.rsocket.core.RSocketClient}
-		 * which establishes a shared TCP connection to given host and port.
-		 * @param host the host of the server to connect to
-		 * @param port the port of the server to connect to
+		 * Build an {@link RSocketRequester} with an
+		 * {@link io.rsocket.core.RSocketClient} that connects over TCP to the
+		 * given host and port. The requester can be used to make requests
+		 * concurrently. Requests are made over a shared connection that is also
+		 * re-established as needed when further requests are made.
+		 * @param host the host to connect to
+		 * @param port the port to connect to
 		 * @return the created {@code RSocketRequester}
 		 * @since 5.3
 		 */
 		RSocketRequester tcp(String host, int port);
 
 		/**
-		 * Build an {@link RSocketRequester} instance for use with a WebSocket
-		 * transport. Requests are made via {@link io.rsocket.core.RSocketClient}
-		 * which establishes a shared WebSocket connection to given URL.
-		 * @param uri the URL of the server to connect to
+		 * Build an {@link RSocketRequester} with an
+		 * {@link io.rsocket.core.RSocketClient} that connects over WebSocket to
+		 * the given URL. The requester can be used to make requests
+		 * concurrently. Requests are made over a shared connection that is also
+		 * re-established as needed when further requests are made.
+		 * @param uri the URL to connect to
 		 * @return the created {@code RSocketRequester}
 		 * @since 5.3
 		 */
 		RSocketRequester websocket(URI uri);
 
 		/**
-		 * Build an {@link RSocketRequester} instance for use with the given
-		 * transport. Requests are made via {@link io.rsocket.core.RSocketClient}
-		 * which establishes a shared connection through the given transport.
-		 * @param transport the transport to use for connecting to the server
+		 * Variant of {@link #tcp(String, int)} and {@link #websocket(URI)}
+		 * with an already initialized {@link ClientTransport}.
+		 * @param transport the transport to connect with
 		 * @return the created {@code RSocketRequester}
 		 * @since 5.3
 		 */
 		RSocketRequester transport(ClientTransport transport);
 
+		/**
+		 * 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 created {@code RSocketRequester}
+		 * @since 5.3
+		 */
+		RSocketRequester transports(
+				Publisher<List<LoadbalanceTarget>> targetPublisher,
+				LoadbalanceStrategy loadbalanceStrategy);
+
 		/**
 		 * Connect to the server over TCP.
 		 * @param host the server host