Register annotated handlers in RSocketRequester

Prior to this commit, there would be no easy way to register client
RSocket handlers against an `RSocketRequester` instance. The only
solution was to gather all handlers and wrap them in a
`RSocketMessageHandler` and configure it as an acceptor on the client
RSocket.

This commit adds a convenience method on the `RSocketRequester` builder
to tkae care of this part of the infrastructure.

Closes gh-23170

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

@@ -18,17 +18,20 @@ package org.springframework.messaging.rsocket;
 
 import java.net.URI;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.List;
 import java.util.function.Consumer;
 import java.util.stream.Stream;
 
 import io.rsocket.RSocketFactory;
+import io.rsocket.frame.decoder.PayloadDecoder;
 import io.rsocket.transport.ClientTransport;
 import io.rsocket.transport.netty.client.TcpClientTransport;
 import io.rsocket.transport.netty.client.WebsocketClientTransport;
 import reactor.core.publisher.Mono;
 
 import org.springframework.lang.Nullable;
+import org.springframework.messaging.rsocket.annotation.support.RSocketMessageHandler;
 import org.springframework.util.Assert;
 import org.springframework.util.MimeType;
 
@@ -53,6 +56,7 @@ final class DefaultRSocketRequesterBuilder implements RSocketRequester.Builder {
 
 	private List<Consumer<RSocketStrategies.Builder>> strategiesConfigurers = new ArrayList<>();
 
+	private List<Object> handlers = new ArrayList<>();
 
 	@Override
 	public RSocketRequester.Builder dataMimeType(@Nullable MimeType mimeType) {
@@ -79,6 +83,12 @@ final class DefaultRSocketRequesterBuilder implements RSocketRequester.Builder {
 		return this;
 	}
 
+	@Override
+	public RSocketRequester.Builder annotatedHandlers(Object... handlers) {
+		this.handlers.addAll(Arrays.asList(handlers));
+		return this;
+	}
+
 	@Override
 	public RSocketRequester.Builder rsocketStrategies(Consumer<RSocketStrategies.Builder> configurer) {
 		this.strategiesConfigurers.add(configurer);
@@ -101,7 +111,6 @@ final class DefaultRSocketRequesterBuilder implements RSocketRequester.Builder {
 	}
 
 	private Mono<RSocketRequester> doConnect(ClientTransport transport) {
-
 		RSocketStrategies rsocketStrategies = getRSocketStrategies();
 		Assert.isTrue(!rsocketStrategies.encoders().isEmpty(), "No encoders");
 		Assert.isTrue(!rsocketStrategies.decoders().isEmpty(), "No decoders");
@@ -110,6 +119,15 @@ final class DefaultRSocketRequesterBuilder implements RSocketRequester.Builder {
 		MimeType dataMimeType = getDataMimeType(rsocketStrategies);
 		rsocketFactory.dataMimeType(dataMimeType.toString());
 		rsocketFactory.metadataMimeType(this.metadataMimeType.toString());
+
+		if (!this.handlers.isEmpty()) {
+			RSocketMessageHandler messageHandler = new RSocketMessageHandler();
+			messageHandler.setHandlers(this.handlers);
+			messageHandler.setRSocketStrategies(rsocketStrategies);
+			messageHandler.afterPropertiesSet();
+			rsocketFactory.acceptor(messageHandler.clientAcceptor());
+		}
+		rsocketFactory.frameDecoder(PayloadDecoder.ZERO_COPY);
 		this.factoryConfigurers.forEach(consumer -> consumer.accept(rsocketFactory));
 
 		return rsocketFactory.transport(transport)

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

@@ -30,6 +30,7 @@ import reactor.core.publisher.Mono;
 import org.springframework.core.ParameterizedTypeReference;
 import org.springframework.core.ReactiveAdapterRegistry;
 import org.springframework.lang.Nullable;
+import org.springframework.messaging.rsocket.annotation.support.RSocketMessageHandler;
 import org.springframework.util.MimeType;
 
 /**
@@ -158,6 +159,17 @@ public interface RSocketRequester {
 		 */
 		RSocketRequester.Builder rsocketStrategies(Consumer<RSocketStrategies.Builder> configurer);
 
+		/**
+		 * Add handlers for processing requests sent by the server.
+		 * <p>This is a shortcut for registering client handlers (i.e. annotated controllers)
+		 * to a {@link RSocketMessageHandler} and configuring it as an acceptor.
+		 * You can take full control by manually registering an acceptor on the
+		 * {@link RSocketFactory.ClientRSocketFactory} using {@link #rsocketFactory(Consumer)}
+		 * instead.
+		 * @param handlers the client handlers to configure on the requester
+		 */
+		RSocketRequester.Builder annotatedHandlers(Object... handlers);
+
 		/**
 		 * Connect to the RSocket server over TCP.
 		 * @param host the server host