Release Netty resources when MQTT transport init fails

common/transport/mqtt/src/main/java/org/thingsboard/server/transport/mqtt/MqttTransportService.java

@@ -80,20 +80,33 @@ public class MqttTransportService implements TbTransportService {
         log.info("Starting MQTT transport...");
         bossGroup = new NioEventLoopGroup(bossGroupThreadCount);
         workerGroup = new NioEventLoopGroup(workerGroupThreadCount);
-        ServerBootstrap b = new ServerBootstrap();
-        b.group(bossGroup, workerGroup)
-                .channel(NioServerSocketChannel.class)
-                .childHandler(new MqttTransportServerInitializer(context, false))
-                .childOption(ChannelOption.SO_KEEPALIVE, keepAlive);
-
-        serverChannel = b.bind(host, port).sync().channel();
-        if (sslEnabled) {
-            b = new ServerBootstrap();
+        try {
+            ServerBootstrap b = new ServerBootstrap();
             b.group(bossGroup, workerGroup)
                     .channel(NioServerSocketChannel.class)
-                    .childHandler(new MqttTransportServerInitializer(context, true))
+                    .childHandler(new MqttTransportServerInitializer(context, false))
                     .childOption(ChannelOption.SO_KEEPALIVE, keepAlive);
-            sslServerChannel = b.bind(sslHost, sslPort).sync().channel();
+
+            serverChannel = b.bind(host, port).sync().channel();
+            if (sslEnabled) {
+                b = new ServerBootstrap();
+                b.group(bossGroup, workerGroup)
+                        .channel(NioServerSocketChannel.class)
+                        .childHandler(new MqttTransportServerInitializer(context, true))
+                        .childOption(ChannelOption.SO_KEEPALIVE, keepAlive);
+                sslServerChannel = b.bind(sslHost, sslPort).sync().channel();
+            }
+        } catch (Exception e) {
+            log.error("Failed to start MQTT transport, releasing resources", e);
+            if (serverChannel != null) {
+                serverChannel.close();
+            }
+            if (sslServerChannel != null) {
+                sslServerChannel.close();
+            }
+            workerGroup.shutdownGracefully();
+            bossGroup.shutdownGracefully();
+            throw e;
         }
         log.info("Mqtt transport started!");
     }

common/transport/mqtt/src/test/java/org/thingsboard/server/transport/mqtt/MqttTransportServiceTest.java

@@ -0,0 +1,121 @@
+/**
+ * Copyright © 2016-2026 The Thingsboard Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.thingsboard.server.transport.mqtt;
+
+import io.netty.channel.Channel;
+import io.netty.channel.EventLoopGroup;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+import org.springframework.test.util.ReflectionTestUtils;
+
+import java.net.BindException;
+import java.net.InetAddress;
+import java.net.ServerSocket;
+import java.util.concurrent.TimeUnit;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+import static org.awaitility.Awaitility.await;
+
+@ExtendWith(MockitoExtension.class)
+public class MqttTransportServiceTest {
+
+    private static final String HOST = "127.0.0.1";
+
+    @Mock
+    private MqttTransportContext context;
+
+    private MqttTransportService service;
+    private ServerSocket occupiedSocket;
+    private int occupiedPort;
+
+    @BeforeEach
+    public void setUp() throws Exception {
+        occupiedSocket = new ServerSocket(0, 50, InetAddress.getByName(HOST));
+        occupiedPort = occupiedSocket.getLocalPort();
+
+        service = new MqttTransportService();
+        ReflectionTestUtils.setField(service, "host", HOST);
+        ReflectionTestUtils.setField(service, "port", occupiedPort);
+        ReflectionTestUtils.setField(service, "sslEnabled", false);
+        ReflectionTestUtils.setField(service, "sslHost", HOST);
+        ReflectionTestUtils.setField(service, "sslPort", 0);
+        ReflectionTestUtils.setField(service, "leakDetectorLevel", "DISABLED");
+        ReflectionTestUtils.setField(service, "bossGroupThreadCount", 1);
+        ReflectionTestUtils.setField(service, "workerGroupThreadCount", 1);
+        ReflectionTestUtils.setField(service, "keepAlive", true);
+        ReflectionTestUtils.setField(service, "context", context);
+    }
+
+    @AfterEach
+    public void tearDown() throws Exception {
+        if (occupiedSocket != null && !occupiedSocket.isClosed()) {
+            occupiedSocket.close();
+        }
+    }
+
+    @Test
+    public void whenPlainBindFails_thenInitThrowsAndReleasesNettyResources() {
+        assertThatThrownBy(() -> service.init())
+                .isInstanceOf(BindException.class);
+
+        Channel serverChannel = (Channel) ReflectionTestUtils.getField(service, "serverChannel");
+        Channel sslServerChannel = (Channel) ReflectionTestUtils.getField(service, "sslServerChannel");
+        EventLoopGroup boss = (EventLoopGroup) ReflectionTestUtils.getField(service, "bossGroup");
+        EventLoopGroup worker = (EventLoopGroup) ReflectionTestUtils.getField(service, "workerGroup");
+
+        assertThat(serverChannel).isNull();
+        assertThat(sslServerChannel).isNull();
+        assertThat(boss).isNotNull();
+        assertThat(worker).isNotNull();
+        assertThat(boss.isShuttingDown()).isTrue();
+        assertThat(worker.isShuttingDown()).isTrue();
+
+        await().atMost(30, TimeUnit.SECONDS).until(boss::isTerminated);
+        await().atMost(30, TimeUnit.SECONDS).until(worker::isTerminated);
+    }
+
+    @Test
+    public void whenSslBindFailsAfterPlainBound_thenInitThrowsAndClosesPlainChannelAndReleasesNettyResources() {
+        ReflectionTestUtils.setField(service, "port", 0);
+        ReflectionTestUtils.setField(service, "sslEnabled", true);
+        ReflectionTestUtils.setField(service, "sslPort", occupiedPort);
+
+        assertThatThrownBy(() -> service.init())
+                .isInstanceOf(BindException.class);
+
+        Channel serverChannel = (Channel) ReflectionTestUtils.getField(service, "serverChannel");
+        Channel sslServerChannel = (Channel) ReflectionTestUtils.getField(service, "sslServerChannel");
+        EventLoopGroup boss = (EventLoopGroup) ReflectionTestUtils.getField(service, "bossGroup");
+        EventLoopGroup worker = (EventLoopGroup) ReflectionTestUtils.getField(service, "workerGroup");
+
+        assertThat(serverChannel).isNotNull();
+        assertThat(sslServerChannel).isNull();
+        assertThat(boss).isNotNull();
+        assertThat(worker).isNotNull();
+
+        await().atMost(10, TimeUnit.SECONDS).until(() -> !serverChannel.isOpen());
+
+        assertThat(boss.isShuttingDown()).isTrue();
+        assertThat(worker.isShuttingDown()).isTrue();
+        await().atMost(30, TimeUnit.SECONDS).until(boss::isTerminated);
+        await().atMost(30, TimeUnit.SECONDS).until(worker::isTerminated);
+    }
+}