Provide access to underlying RSocketClient

The recently introduced support for RSocketClient in commit
7c98251142 did not expose the underlying
client in order to avoid a hard dependency on RSocket 1.1 for the time
being. However such access appears to be necessary, e.g. for Spring
Integration, where the connection needs to be established (warmed up)
ahead of actual requests.

See gh-25332

spring-messaging/src/test/java/org/springframework/messaging/rsocket/DefaultRSocketRequesterBuilderTests.java

@@ -206,8 +206,8 @@ public class DefaultRSocketRequesterBuilderTests {
 	}
 
 	private ConnectionSetupPayload getConnectionSetupPayload(RSocketRequester requester) {
-		// Trigger connection and sending of SETUP frame
-		requester.route("any-route").data("any-data").send().block();
+		// Trigger connection establishment
+		requester.rsocketClient().source().block();
 		return new DefaultConnectionSetupPayload(this.connection.setupFrame());
 	}
 

spring-messaging/src/test/java/org/springframework/messaging/rsocket/RSocketBufferLeakTests.java

@@ -94,7 +94,7 @@ class RSocketBufferLeakTests {
 
 	@AfterAll
 	void tearDownOnce() {
-		requester.dispose();
+		requester.rsocketClient().dispose();
 		server.dispose();
 		context.close();
 	}

spring-messaging/src/test/java/org/springframework/messaging/rsocket/RSocketClientToServerIntegrationTests.java

@@ -96,7 +96,7 @@ public class RSocketClientToServerIntegrationTests {
 
 	@AfterAll
 	public static void tearDownOnce() {
-		requester.dispose();
+		requester.rsocketClient().dispose();
 		server.dispose();
 	}
 

spring-messaging/src/test/java/org/springframework/messaging/rsocket/RSocketServerToClientIntegrationTests.java

@@ -110,14 +110,14 @@ public class RSocketServerToClientIntegrationTests {
 					.rsocketConnector(connector -> connector.acceptor(responder))
 					.tcp("localhost", server.address().getPort());
 
-			// Make a request to cause a connection to be established.
-			requester.route("fnf").send().block();
+			// Trigger connection establishment.
+			requester.rsocketClient().source().block();
 
 			context.getBean(ServerController.class).await(Duration.ofSeconds(5));
 		}
 		finally {
 			if (requester != null) {
-				requester.dispose();
+				requester.rsocketClient().dispose();
 			}
 		}
 	}

spring-messaging/src/test/kotlin/org/springframework/messaging/rsocket/RSocketClientToServerCoroutinesIntegrationTests.kt

@@ -271,7 +271,7 @@ class RSocketClientToServerCoroutinesIntegrationTests {
 		@AfterAll
 		@JvmStatic
 		fun tearDownOnce() {
-			requester.dispose()
+			requester.rsocketClient().dispose()
 			server.dispose()
 		}
 	}