forgot to set the acquire puback to 0 for qos 0 publishes

Author: sbSteveK

src/main/java/software/amazon/awssdk/crt/mqtt5/PublishReturn.java

@@ -18,6 +18,7 @@ public class PublishReturn {
      * Single-element long array holding the native manual PUBACK control context pointer.
      * Element [0] is the pointer value, valid only during the
      * {@link Mqtt5ClientOptions.PublishEvents#onMessageReceived} callback.
+     * QoS 0 results in this being set to 0.
      * Native code sets [0] to 0 after the callback returns (via SetLongArrayRegion,
      * requiring no extra JNI method ID).
      */

src/native/mqtt5_client.c

@@ -605,7 +605,11 @@ static void s_aws_mqtt5_client_java_publish_received(
     context_ptr_holder = (*env)->NewLongArray(env, 1);
     /* If allocation failed, Java will throw IllegalStateException on acquirePubackControl(). */
     if (context_ptr_holder != NULL) {
-        jlong context_ptr_value = (jlong)(uintptr_t)control_context;
+        /*
+         * Only expose the context pointer for QoS 1 publishes. For QoS 0, there is no PUBACK
+         * to send, so acquirePubackControl() should throw IllegalStateException. We pass 0 (null).
+         */
+        jlong context_ptr_value = (publish->qos == AWS_MQTT5_QOS_AT_MOST_ONCE) ? 0 : (jlong)(uintptr_t)control_context;
         /* Assigning the pointer to the allocated manual_puback_control_context to the single-element of the array */
         (*env)->SetLongArrayRegion(env, context_ptr_holder, 0, 1, &context_ptr_value);
     }

src/test/java/software/amazon/awssdk/crt/test/Mqtt5ClientTest.java

@@ -2884,7 +2884,7 @@ private void doManualPuback_Qos0AcquireThrowsTest() {
                 @Override
                 public void onMessageReceived(Mqtt5Client client, PublishReturn publishReturn) {
                     // For QoS 0, acquirePubackControl() should throw IllegalStateException
-                    // because there is no PUBACK context (nativeContextPtrHolder is null or 0)
+                    // because the native layer passes a null context pointer for QoS 0 publishes.
                     try {
                         publishReturn.acquirePubackControl();
                         resultFuture.complete("no_error"); // Should not reach here
@@ -2904,7 +2904,7 @@ public void onMessageReceived(Mqtt5Client client, PublishReturn publishReturn) {
                 SubscribePacketBuilder subscribeBuilder = new SubscribePacketBuilder(testTopic, QOS.AT_LEAST_ONCE);
                 client.subscribe(subscribeBuilder.build()).get(OPERATION_TIMEOUT_TIME, TimeUnit.SECONDS);
 
-                // Publish at QoS 0, no PUBACK involved
+                // Publish at QoS 0, there is no PUBACK involved
                 PublishPacketBuilder publishBuilder = new PublishPacketBuilder(testTopic, QOS.AT_MOST_ONCE, payload);
                 client.publish(publishBuilder.build()).get(OPERATION_TIMEOUT_TIME, TimeUnit.SECONDS);