Fix new Sonar smells

* Use `tryEmitNext` on Reactor `Sink` since `emitNext` is deprecated
* Add `MessageDeliveryException` emission when `send()` returns `false`
in the `FluxMessageChannel` for `subscribeTo` provided `Publisher`

spring-integration-core/src/main/java/org/springframework/integration/channel/FluxMessageChannel.java

@@ -23,6 +23,7 @@
 import org.reactivestreams.Subscriber;
 
 import org.springframework.messaging.Message;
+import org.springframework.messaging.MessageDeliveryException;
 import org.springframework.util.Assert;
 
 import reactor.core.Disposable;
@@ -71,7 +72,8 @@ protected boolean doSend(Message<?> message, long timeout) {
 		long parkTimeout = 10; // NOSONAR
 		long parkTimeoutNs = TimeUnit.MILLISECONDS.toNanos(parkTimeout);
 		while (this.active && !tryEmitMessage(message)) {
-			if (timeout >= 0 && (remainingTime -= parkTimeout) <= 0) {
+			remainingTime -= parkTimeout;
+			if (timeout >= 0 && remainingTime <= 0) {
 				return false;
 			}
 			LockSupport.parkNanos(parkTimeoutNs);
@@ -95,9 +97,9 @@ private boolean tryEmitMessage(Message<?> message) {
 	@Override
 	public void subscribe(Subscriber<? super Message<?>> subscriber) {
 		this.processor
-				.doFinally((s) -> this.subscribedSignal.emitNext(this.processor.hasDownstreams()))
+				.doFinally((s) -> this.subscribedSignal.tryEmitNext(this.processor.hasDownstreams()))
 				.subscribe(subscriber);
-		this.subscribedSignal.emitNext(this.processor.hasDownstreams());
+		this.subscribedSignal.tryEmitNext(this.processor.hasDownstreams());
 	}
 
 	@Override
@@ -108,7 +110,10 @@ public void subscribeTo(Publisher<? extends Message<?>> publisher) {
 						.publishOn(Schedulers.boundedElastic())
 						.doOnNext((message) -> {
 							try {
-								send(message);
+								if (!send(message)) {
+									throw new MessageDeliveryException(message,
+											"Failed to send message to channel '" + this);
+								}
 							}
 							catch (Exception ex) {
 								logger.warn("Error during processing event: " + message, ex);
@@ -120,7 +125,7 @@ public void subscribeTo(Publisher<? extends Message<?>> publisher) {
 	@Override
 	public void destroy() {
 		this.active = false;
-		this.subscribedSignal.emitNext(false);
+		this.subscribedSignal.tryEmitNext(false);
 		this.upstreamSubscriptions.dispose();
 		this.processor.onComplete();
 		super.destroy();

spring-integration-core/src/main/java/org/springframework/integration/util/IntegrationReactiveUtils.java

@@ -100,7 +100,7 @@ public static <T> Flux<Message<T>> messageSourceToFlux(MessageSource<T> messageS
 	 * - a {@link org.springframework.integration.channel.FluxMessageChannel}
 	 * is returned as is because it is already a {@link Publisher};
 	 * - a {@link SubscribableChannel} is subscribed with a {@link MessageHandler}
-	 * for the {@link Sinks.Many#emitNext(Object)} which is returned from this method;
+	 * for the {@link Sinks.Many#tryEmitNext(Object)} which is returned from this method;
 	 * - a {@link PollableChannel} is wrapped into a {@link MessageSource} lambda and reuses
 	 * {@link #messageSourceToFlux(MessageSource)}.
 	 * @param messageChannel the {@link MessageChannel} to adapt.

spring-integration-core/src/test/java/org/springframework/integration/channel/reactive/ReactiveStreamsConsumerTests.java

@@ -301,7 +301,7 @@ public void testReactiveStreamsConsumerFluxMessageChannelReactiveMessageHandler(
 
 		ReactiveMessageHandler messageHandler =
 				m -> {
-					sink.emitNext(m);
+					sink.tryEmitNext(m);
 					return Mono.empty();
 				};
 

spring-integration-rsocket/src/test/java/org/springframework/integration/rsocket/outbound/RSocketOutboundGatewayIntegrationTests.java

@@ -544,7 +544,7 @@ static class TestController {
 
 		@MessageMapping("receive")
 		void receive(String payload) {
-			this.fireForgetPayloads.emitNext(payload);
+			this.fireForgetPayloads.tryEmitNext(payload);
 		}
 
 		@MessageMapping("echo")