[Transform] Call listener in order to prevent the request from hanging

docs/changelog/96221.yaml

@@ -0,0 +1,5 @@
+pr: 96221
+summary: Call listener in order to prevent the request from hanging
+area: Transform
+type: bug
+issues: []

x-pack/plugin/transform/qa/single-node-tests/src/javaRestTest/java/org/elasticsearch/xpack/transform/integration/TransformUpdateIT.java

@@ -23,6 +23,7 @@
 import java.util.concurrent.TimeUnit;
 
 import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.is;
 
 public class TransformUpdateIT extends TransformRestTestCase {
 
@@ -148,6 +149,24 @@ public void testUpdateTransferRightsSecondaryAuthHeaders() throws Exception {
         updateTransferRightsTester(true);
     }
 
+    public void testUpdateThatChangesSettingsButNotHeaders() throws Exception {
+        String transformId = "test_update_that_changes_settings";
+        String destIndex = transformId + "-dest";
+
+        // Create the transform
+        createPivotReviewsTransform(transformId, destIndex, null, null, null);
+
+        Request updateTransformRequest = createRequestWithAuth("POST", getTransformEndpoint() + transformId + "/_update", null);
+        updateTransformRequest.setJsonEntity("""
+            { "settings": { "max_page_search_size": 123 } }""");
+
+        // Update the transform's settings
+        Map<String, Object> updatedConfig = entityAsMap(client().performRequest(updateTransformRequest));
+
+        // Verify that the settings got updated
+        assertThat(updatedConfig.get("settings"), is(equalTo(Map.of("max_page_search_size", 123))));
+    }
+
     private void updateTransferRightsTester(boolean useSecondaryAuthHeaders) throws Exception {
         String transformId = "transform1";
         // Note: Due to a bug the transform does not fail to start after deleting the user and role, therefore invalidating

x-pack/plugin/transform/src/main/java/org/elasticsearch/xpack/transform/action/TransportUpdateTransformAction.java

@@ -205,6 +205,8 @@ protected void doExecute(Task task, Request request, ActionListener<Response> li
                                     authState,
                                     ActionListener.wrap(aVoid -> listener.onResponse(new Response(updatedConfig)), listener::onFailure)
                                 );
+                            } else {
+                                listener.onResponse(new Response(updatedConfig));
                             }
                         } else {
                             listener.onResponse(new Response(updatedConfig));