Message broker skips messages with user destination

When a broker message handler is not configured with any prefixes, it will
process all messages by default, but user destination messages should be
pre-processed by the userDestinationMessageHandler first. This change
protects against that.

Closes gh-26474

spring-messaging/src/main/java/org/springframework/messaging/simp/broker/AbstractBrokerMessageHandler.java

@@ -19,6 +19,7 @@ package org.springframework.messaging.simp.broker;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.function.Predicate;
 
 import org.apache.commons.logging.Log;
 
@@ -58,6 +59,9 @@ public abstract class AbstractBrokerMessageHandler
 
 	private final Collection<String> destinationPrefixes;
 
+	@Nullable
+	private Predicate<String> userDestinationPredicate;
+
 	private boolean preservePublishOrder = false;
 
 	@Nullable
@@ -135,6 +139,21 @@ public abstract class AbstractBrokerMessageHandler
 		return this.destinationPrefixes;
 	}
 
+	/**
+	 * Configure a Predicate to identify messages with a user destination. When
+	 * no {@link #getDestinationPrefixes() destination prefixes} are configured,
+	 * this helps to recognize and skip user destination messages that need to
+	 * be pre-processed by the
+	 * {@link org.springframework.messaging.simp.user.UserDestinationMessageHandler}
+	 * before they reach the broker.
+	 * @param predicate the predicate to identify user messages with a non-null
+	 * destination as messages with a user destinations.
+	 * @since 5.3.4
+	 */
+	public void setUserDestinationPredicate(@Nullable Predicate<String> predicate) {
+		this.userDestinationPredicate = predicate;
+	}
+
 	/**
 	 * Whether the client must receive messages in the order of publication.
 	 * <p>By default messages sent to the {@code "clientOutboundChannel"} may
@@ -265,10 +284,27 @@ public abstract class AbstractBrokerMessageHandler
 	protected abstract void handleMessageInternal(Message<?> message);
 
 
+	/**
+	 * Whether a message with the given destination should be processed. This is
+	 * the case if one of the following conditions is true:
+	 * <ol>
+	 * <li>The destination starts with one of the configured
+	 * {@link #getDestinationPrefixes() destination prefixes}.
+	 * <li>No prefixes are configured and the destination isn't matched
+	 * by the {@link #setUserDestinationPredicate(Predicate)
+	 * userDestinationPredicate}.
+	 * <li>The message has no destination.
+	 * </ol>
+	 * @param destination the destination to check
+	 * @return whether to process (true) or skip (false) the destination
+	 */
 	protected boolean checkDestinationPrefix(@Nullable String destination) {
-		if (destination == null || CollectionUtils.isEmpty(this.destinationPrefixes)) {
+		if (destination == null) {
 			return true;
 		}
+		if (CollectionUtils.isEmpty(this.destinationPrefixes)) {
+			return !isUserDestination(destination);
+		}
 		for (String prefix : this.destinationPrefixes) {
 			if (destination.startsWith(prefix)) {
 				return true;
@@ -277,6 +313,10 @@ public abstract class AbstractBrokerMessageHandler
 		return false;
 	}
 
+	private boolean isUserDestination(String destination) {
+		return (this.userDestinationPredicate != null && this.userDestinationPredicate.test(destination));
+	}
+
 	protected void publishBrokerAvailableEvent() {
 		boolean shouldPublish = this.brokerAvailable.compareAndSet(false, true);
 		if (this.eventPublisher != null && shouldPublish) {

spring-messaging/src/main/java/org/springframework/messaging/simp/config/AbstractMessageBrokerConfiguration.java

@@ -64,6 +64,7 @@ import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
 import org.springframework.util.MimeTypeUtils;
 import org.springframework.util.PathMatcher;
+import org.springframework.util.StringUtils;
 import org.springframework.validation.Errors;
 import org.springframework.validation.Validator;
 
@@ -346,15 +347,21 @@ public abstract class AbstractMessageBrokerConfiguration implements ApplicationC
 		if (handler == null) {
 			return null;
 		}
-		updateUserDestinationResolver(handler, userDestinationResolver);
+		updateUserDestinationResolver(handler, userDestinationResolver, registry.getUserDestinationPrefix());
 		return handler;
 	}
 
-	private void updateUserDestinationResolver(AbstractBrokerMessageHandler handler, UserDestinationResolver userDestinationResolver) {
+	private void updateUserDestinationResolver(
+			AbstractBrokerMessageHandler handler, UserDestinationResolver userDestinationResolver,
+			@Nullable String userDestinationPrefix) {
+
 		Collection<String> prefixes = handler.getDestinationPrefixes();
 		if (!prefixes.isEmpty() && !prefixes.iterator().next().startsWith("/")) {
 			((DefaultUserDestinationResolver) userDestinationResolver).setRemoveLeadingSlash(true);
 		}
+		if (StringUtils.hasText(userDestinationPrefix)) {
+			handler.setUserDestinationPredicate(destination -> destination.startsWith(userDestinationPrefix));
+		}
 	}
 
 	@Bean
@@ -379,7 +386,7 @@ public abstract class AbstractMessageBrokerConfiguration implements ApplicationC
 			subscriptions.put(destination, userRegistryMessageHandler);
 		}
 		handler.setSystemSubscriptions(subscriptions);
-		updateUserDestinationResolver(handler, userDestinationResolver);
+		updateUserDestinationResolver(handler, userDestinationResolver, registry.getUserDestinationPrefix());
 		return handler;
 	}