Publish RabbitMQ messages as JSON instead of Java serialization

src/inttest/java/com/faforever/api/config/RabbitMessageEncodingTest.java

@@ -0,0 +1,105 @@
+package com.faforever.api.config;
+
+import com.faforever.api.AbstractIntegrationTest;
+import com.faforever.api.data.domain.Avatar;
+import com.faforever.api.data.domain.Player;
+import com.faforever.api.data.hook.PlayerAvatarUpdateHook;
+import com.yahoo.elide.annotation.LifeCycleHookBinding.Operation;
+import com.yahoo.elide.annotation.LifeCycleHookBinding.TransactionPhase;
+import org.json.JSONException;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.Test;
+import org.skyscreamer.jsonassert.JSONAssert;
+import org.springframework.amqp.core.AmqpAdmin;
+import org.springframework.amqp.core.BindingBuilder;
+import org.springframework.amqp.core.Message;
+import org.springframework.amqp.core.MessageProperties;
+import org.springframework.amqp.core.Queue;
+import org.springframework.amqp.core.TopicExchange;
+import org.springframework.amqp.rabbit.core.RabbitTemplate;
+import org.springframework.beans.factory.annotation.Autowired;
+
+import java.nio.charset.StandardCharsets;
+import java.util.Optional;
+
+import static com.faforever.api.config.RabbitConfiguration.EXCHANGE_FAF_LOBBY;
+import static com.faforever.api.data.hook.PlayerAvatarUpdateHook.ROUTING_KEY_PLAYER_AVATAR_UPDATE;
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Verifies that messages published through the auto-configured {@link RabbitTemplate} are serialized as JSON
+ * (content type {@code application/json}) rather than the default {@code application/x-java-serialized-object},
+ * i.e. that the application-wide {@link RabbitConfiguration#jacksonJsonMessageConverter()} bean is actually
+ * applied to the publishing side.
+ */
+public class RabbitMessageEncodingTest extends AbstractIntegrationTest {
+
+  private static final String TEST_QUEUE = "inttest.player_avatar.update";
+
+  @Autowired
+  private RabbitTemplate rabbitTemplate;
+  @Autowired
+  private AmqpAdmin amqpAdmin;
+  @Autowired
+  private PlayerAvatarUpdateHook playerAvatarUpdateHook;
+
+  private void bindTestQueue() {
+    Queue queue = new Queue(TEST_QUEUE, false, false, true);
+    amqpAdmin.declareQueue(queue);
+    amqpAdmin.declareBinding(
+      BindingBuilder.bind(queue).to(new TopicExchange(EXCHANGE_FAF_LOBBY)).with(ROUTING_KEY_PLAYER_AVATAR_UPDATE));
+  }
+
+  @AfterEach
+  public void deleteTestQueue() {
+    amqpAdmin.deleteQueue(TEST_QUEUE);
+  }
+
+  @Test
+  public void avatarUpdateIsPublishedAsJson() throws JSONException {
+    bindTestQueue();
+
+    Player player = new Player();
+    player.setId(42);
+    Avatar avatar = new Avatar();
+    avatar.setId(5);
+    player.setCurrentAvatar(avatar);
+
+    playerAvatarUpdateHook.execute(Operation.UPDATE, TransactionPhase.POSTCOMMIT, player, null, Optional.empty());
+
+    Message message = rabbitTemplate.receive(TEST_QUEUE, 5000);
+
+    assertThat(message).isNotNull();
+    assertThat(message.getMessageProperties().getContentType()).isEqualTo(MessageProperties.CONTENT_TYPE_JSON);
+    JSONAssert.assertEquals("""
+      {
+        "player_id": 42,
+        "avatar_id": 5
+      }""",
+      new String(message.getBody(), StandardCharsets.UTF_8),
+      true);
+  }
+
+  @Test
+  public void clearedAvatarIsPublishedAsJsonWithNull() throws JSONException {
+    bindTestQueue();
+
+    Player player = new Player();
+    player.setId(42);
+    player.setCurrentAvatar(null);
+
+    playerAvatarUpdateHook.execute(Operation.UPDATE, TransactionPhase.POSTCOMMIT, player, null, Optional.empty());
+
+    Message message = rabbitTemplate.receive(TEST_QUEUE, 5000);
+
+    assertThat(message).isNotNull();
+    assertThat(message.getMessageProperties().getContentType()).isEqualTo(MessageProperties.CONTENT_TYPE_JSON);
+    JSONAssert.assertEquals("""
+      {
+        "player_id": 42,
+        "avatar_id": null
+      }""",
+      new String(message.getBody(), StandardCharsets.UTF_8),
+      true);
+  }
+}

src/main/java/com/faforever/api/config/RabbitConfiguration.java

@@ -55,16 +55,29 @@ public StatelessRetryOperationsInterceptor retryInterceptor() {
    * Reconfigure default Rabbit container, so it doesn't infinitely requeue.
    * Instead, we use a retry that does a limited requeueing.
    */
+  /**
+   * JSON message converter used for both publishing (applied to the auto-configured
+   * {@link org.springframework.amqp.rabbit.core.RabbitTemplate} by Spring Boot when a single
+   * {@link org.springframework.amqp.support.converter.MessageConverter} bean is present) and consuming.
+   * Without this, the default {@code SimpleMessageConverter} would Java-serialize outgoing payloads
+   * ({@code application/x-java-serialized-object}) instead of producing JSON.
+   */
+  @Bean
+  public JacksonJsonMessageConverter jacksonJsonMessageConverter() {
+    return new JacksonJsonMessageConverter();
+  }
+
   @Bean
   public SimpleRabbitListenerContainerFactory rabbitListenerContainerFactory(
     ConnectionFactory connectionFactory,
-    StatelessRetryOperationsInterceptor retryInterceptor
+    StatelessRetryOperationsInterceptor retryInterceptor,
+    JacksonJsonMessageConverter jacksonJsonMessageConverter
   ) {
     var factory = new SimpleRabbitListenerContainerFactory();
     factory.setDefaultRequeueRejected(false);
     factory.setConnectionFactory(connectionFactory);
     factory.setAdviceChain(retryInterceptor);
-    factory.setMessageConverter(new JacksonJsonMessageConverter());
+    factory.setMessageConverter(jacksonJsonMessageConverter);
 
     return factory;
   }