Wildcard subscription for a topic with a large number retained messages

[gg-dim]

We are running a Mosquitto 2.0.18 in docker on Ubuntu server 22.04.4 LTS.
Our scenario includes many retained messages and wildcard subscriptions and we have observed that clients don't receive all messages when subscribing.

Scenario to reproduce

• 4 topics (e.g. test.candelete1/, test.candelete2/, test.candelete3/, test.candelete4/)
• publish 10000 messages for each topic, each message in a sub-topic (e.g. test.candelete1/1234567890-1234567890-1234567890-1)
• Create and connect one client
• subscribe the client to the 4 topics with a wildcard '#'
• the client should receive 40000 messages, but in our test cases we only receive 30000 or 20000, depending on how long the topics and the messages are and how high the network latency is.

When you publish a new message to one the subscribed topic, Mosquitto starts sending the remaining missing messages.

We created a test (java, paho client) to reproduce the issue. It can also be reproduced with other clients.

/*
 * Copyright (c) 2012 - 2024 Data In Motion and others.
 * All rights reserved. 
 * 
 * This program and the accompanying materials are made available under the terms of the 
 * Eclipse Public License v1.0 which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 * 
 * Contributors:
 *     Data In Motion
 *******************************************************************************/

package org.eclipse.paho.client.mqttv3.test;

import static org.junit.Assert.assertTrue;

import java.net.URI;
import java.util.UUID;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;
import java.util.logging.Level;
import java.util.logging.Logger;

import org.eclipse.paho.client.mqttv3.IMqttClient;
import org.eclipse.paho.client.mqttv3.IMqttMessageListener;
import org.eclipse.paho.client.mqttv3.MqttException;
import org.eclipse.paho.client.mqttv3.MqttMessage;
import org.eclipse.paho.client.mqttv3.MqttPersistenceException;
import org.eclipse.paho.client.mqttv3.test.client.MqttClientFactoryPaho;
import org.eclipse.paho.client.mqttv3.test.logging.LoggingUtilities;
import org.eclipse.paho.client.mqttv3.test.properties.TestProperties;
import org.eclipse.paho.client.mqttv3.test.utilities.Utility;
import org.junit.AfterClass;
import org.junit.Assert;
import org.junit.BeforeClass;
import org.junit.Test;

/**
 * Tests shows an issue with a wildcard subscription to a topic with lots of
 * retained messages.
 */
public class RetainedTest {

	static final Class<?> cclass = RetainedTest.class;
	private static final String className = cclass.getName();
	private static final Logger log = Logger.getLogger(className);

	private static final int MESSAGE_COUNT = 40000;
	private static final int TOPIC_COUNT = 4;
	private static URI serverURI;
	private static MqttClientFactoryPaho clientFactory;
	private static String topicPrefix;

	/**
	@BeforeClass
	public static void setUpBeforeClass() throws Exception {

		try {
			String methodName = Utility.getMethodName();
			LoggingUtilities.banner(log, cclass, methodName);

			serverURI = TestProperties.getServerURI();
			clientFactory = new MqttClientFactoryPaho();
			clientFactory.open();
			topicPrefix = "RetainedTest-" + UUID.randomUUID().toString() + "-";

		} catch (Exception exception) {
			log.log(Level.SEVERE, "caught exception:", exception);
			throw exception;
		}
	}

	@AfterClass
	public static void tearDownAfterClass() throws Exception {
		String methodName = Utility.getMethodName();
		LoggingUtilities.banner(log, cclass, methodName);

		try {
			if (clientFactory != null) {
				clientFactory.close();
				clientFactory.disconnect();
			}
		} catch (Exception exception) {
			log.log(Level.SEVERE, "caught exception:", exception);
		}
	}


	@Test
	public void testSubscribeRetained() throws Exception {
		String methodName = Utility.getMethodName();
		LoggingUtilities.banner(log, cclass, methodName);

		IMqttClient client = null;
		try {
			String clientId = methodName + "-pub";
			client = clientFactory.createMqttClient(serverURI, clientId);

			log.info("Connecting...(serverURI:" + serverURI + ", ClientId:" + clientId);
			client.connect();

			for (int i = 0; i < TOPIC_COUNT; i++) {
				String topic = topicPrefix + i + "/";
				publishMessages(client, topic);
			}

			log.info("Disconnecting... Closing ...");
			client.disconnect();
			client.close();

			log.info("Creating new client ... ");
			clientId = methodName + "-sub";
			final CountDownLatch messageLatch = new CountDownLatch(TOPIC_COUNT * MESSAGE_COUNT);
			client = clientFactory.createMqttClient(serverURI, clientId);

			log.info("Connecting...(serverURI:" + serverURI + ", ClientId:" + clientId);
			client.connect();

			for (int i = 0; i < TOPIC_COUNT; i++) {
				final String t = topicPrefix + i + "/#";
				log.info("Subscribe to " + t);
				client.subscribe(t, 1, new IMqttMessageListener() {
					int messageCounter;
					@Override
					public void messageArrived(String topic, MqttMessage message) throws Exception {
						messageLatch.countDown();
						if (++messageCounter % 5000 == 0) {
							log.info(messageCounter + " messages arrived on " + t);
						}
					}
				});
			}
			log.info("wait for the " + TOPIC_COUNT * MESSAGE_COUNT + " retained messages to arrive.");
			boolean result = messageLatch.await(10, TimeUnit.SECONDS);
			assertTrue(messageLatch.getCount() + " messages didn't arrive.", result);

		} catch (MqttException exception) {
			log.log(Level.SEVERE, "caught exception:", exception);
			Assert.fail("Unexpected exception: " + exception);
		} finally {
			if (client != null) {
				log.info("Disconnecting...");
				client.disconnect();
				log.info("Close...");
				client.close();
			}
		}
	}

	private void publishMessages(IMqttClient client, String topic) throws MqttException, MqttPersistenceException {
		log.info("Publishing " + MESSAGE_COUNT + " retained messages to " + topic + ".");
		for (int i = 0; i < MESSAGE_COUNT; i++) {
			client.publish(topic + "1234567890-1234567890-1234567890-1234567890-" + i,
					("abcdefghijklmnopqrstuvw-abcdefghijklmnopqrstuvw-abcdefghijklmnopqrstuvw-abcdefghijklmnopqrstuvw-abcdefghijklmnopqrstuvw-abcdefghijklmnopqrstuvw-"
							+ i).getBytes(),
					0, true);
		}
	}

}