[Backport 2.x] Fix MLModelTool returns null if the response of LLM is a pure json object (#2675)

* Fix MLModelTool returns null if the response of LLM is a pure json object (#2655)

* Fix MLModelTool returns null if the response of LLM is a pure json object

Signed-off-by: Heng Qian <[email protected]>

* Fix UT failure

Signed-off-by: Heng Qian <[email protected]>

* Avoid NPE

Signed-off-by: Heng Qian <[email protected]>

* spotlessApply

Signed-off-by: Heng Qian <[email protected]>

---------

Signed-off-by: Heng Qian <[email protected]>
(cherry picked from commit 007b914)

* remove java21 API for backporting to 2.x

Signed-off-by: Heng Qian <[email protected]>

---------

Signed-off-by: Heng Qian <[email protected]>

Author: qianheng-aws

ml-algorithms/src/main/java/org/opensearch/ml/engine/tools/MLModelTool.java

@@ -21,6 +21,7 @@
 import org.opensearch.ml.common.spi.tools.ToolAnnotation;
 import org.opensearch.ml.common.transport.prediction.MLPredictionTaskAction;
 import org.opensearch.ml.common.transport.prediction.MLPredictionTaskRequest;
+import org.opensearch.ml.common.utils.StringUtils;
 import org.opensearch.ml.repackage.com.google.common.annotations.VisibleForTesting;
 
 import lombok.Getter;
@@ -54,6 +55,7 @@ public class MLModelTool implements Tool {
     private Parser inputParser;
     @Setter
     @Getter
+    @VisibleForTesting
     private Parser outputParser;
     @Setter
     @Getter
@@ -65,8 +67,18 @@ public MLModelTool(Client client, String modelId, String responseField) {
         this.responseField = responseField;
 
         outputParser = o -> {
-            List<ModelTensors> mlModelOutputs = (List<ModelTensors>) o;
-            return mlModelOutputs.get(0).getMlModelTensors().get(0).getDataAsMap().get(responseField);
+            try {
+                List<ModelTensors> mlModelOutputs = (List<ModelTensors>) o;
+                Map<String, ?> dataAsMap = mlModelOutputs.get(0).getMlModelTensors().get(0).getDataAsMap();
+                // Return the response field if it exists, otherwise return the whole response as json string.
+                if (dataAsMap.containsKey(responseField)) {
+                    return dataAsMap.get(responseField);
+                } else {
+                    return StringUtils.toJson(dataAsMap);
+                }
+            } catch (Exception e) {
+                throw new IllegalStateException("LLM returns wrong or empty tensors", e);
+            }
         };
     }
 

ml-algorithms/src/test/java/org/opensearch/ml/engine/tools/MLModelToolTests.java

@@ -124,7 +124,7 @@ public void testMLModelsWithDefaultOutputParserAndMalformedResponseField() throw
         tool.run(null, listener);
 
         future.join();
-        assertEquals(null, future.get());
+        assertEquals("{\"response\":\"response 1\",\"action\":\"action1\"}", future.get());
     }
 
     @Test
@@ -170,6 +170,26 @@ public void testOutputParserLambda() {
         assertEquals("testResponse", result);
     }
 
+    @Test
+    public void testOutputParserWithJsonResponse() {
+        Parser outputParser = new MLModelTool(client, "modelId", "response").getOutputParser();
+        String expectedJson = "{\"key1\":\"value1\",\"key2\":\"value2\"}";
+
+        // Create a mock ModelTensors with json object
+        ModelTensor modelTensor = ModelTensor.builder().dataAsMap(ImmutableMap.of("key1", "value1", "key2", "value2")).build();
+        ModelTensors modelTensors = ModelTensors.builder().mlModelTensors(Arrays.asList(modelTensor)).build();
+        ModelTensorOutput mlModelTensorOutput = ModelTensorOutput.builder().mlModelOutputs(Arrays.asList(modelTensors)).build();
+        Object result = outputParser.parse(mlModelTensorOutput.getMlModelOutputs());
+        assertEquals(expectedJson, result);
+
+        // Create a mock ModelTensors with response string
+        modelTensor = ModelTensor.builder().dataAsMap(ImmutableMap.of("response", "{\"key1\":\"value1\",\"key2\":\"value2\"}")).build();
+        modelTensors = ModelTensors.builder().mlModelTensors(Arrays.asList(modelTensor)).build();
+        mlModelTensorOutput = ModelTensorOutput.builder().mlModelOutputs(Arrays.asList(modelTensors)).build();
+        result = outputParser.parse(mlModelTensorOutput.getMlModelOutputs());
+        assertEquals(expectedJson, result);
+    }
+
     @Test
     public void testRunWithError() {
         // Mocking the client.execute to simulate an error