add processor chain and add support for model and tool

common/src/main/java/org/opensearch/ml/common/connector/AbstractConnector.java

@@ -111,6 +111,8 @@ public <T> void parseResponse(T response, List<ModelTensor> modelTensors, boolea
         if (response instanceof String && isJson((String) response)) {
             Map<String, Object> data = StringUtils.fromJson((String) response, ML_MAP_RESPONSE_KEY);
             modelTensors.add(ModelTensor.builder().name("response").dataAsMap(data).build());
+        } else if (response instanceof Map) {
+            modelTensors.add(ModelTensor.builder().name("response").dataAsMap((Map<String, ?>) response).build());
         } else {
             Map<String, Object> map = new HashMap<>();
             map.put("response", response);

common/src/main/java/org/opensearch/ml/common/output/model/ModelTensor.java

@@ -18,6 +18,7 @@
 import java.util.List;
 import java.util.Map;
 
+import org.opensearch.common.xcontent.json.JsonXContent;
 import org.opensearch.core.common.io.stream.StreamInput;
 import org.opensearch.core.common.io.stream.StreamOutput;
 import org.opensearch.core.common.io.stream.Writeable;
@@ -289,4 +290,14 @@ public void writeTo(StreamOutput out) throws IOException {
             out.writeBoolean(false);
         }
     }
+
+    @Override
+    public String toString() {
+        try {
+            return this.toXContent(JsonXContent.contentBuilder(), null).toString();
+        } catch (IOException e) {
+            throw new IllegalArgumentException("Can't convert ModelTensor to string", e);
+        }
+    }
+
 }

common/src/main/java/org/opensearch/ml/common/output/model/ModelTensorOutput.java

@@ -11,6 +11,7 @@
 import java.util.ArrayList;
 import java.util.List;
 
+import org.opensearch.common.xcontent.json.JsonXContent;
 import org.opensearch.core.common.io.stream.StreamInput;
 import org.opensearch.core.common.io.stream.StreamOutput;
 import org.opensearch.core.xcontent.XContentBuilder;
@@ -102,4 +103,13 @@ public static ModelTensorOutput parse(XContentParser parser) throws IOException
 
         return ModelTensorOutput.builder().mlModelOutputs(mlModelOutputs).build();
     }
+
+    @Override
+    public String toString() {
+        try {
+            return this.toXContent(JsonXContent.contentBuilder(), null).toString();
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
+    }
 }

common/src/main/java/org/opensearch/ml/common/output/model/ModelTensors.java

@@ -13,6 +13,7 @@
 import java.util.List;
 
 import org.opensearch.common.io.stream.BytesStreamOutput;
+import org.opensearch.common.xcontent.json.JsonXContent;
 import org.opensearch.core.common.bytes.BytesReference;
 import org.opensearch.core.common.io.stream.StreamInput;
 import org.opensearch.core.common.io.stream.StreamOutput;
@@ -171,4 +172,13 @@ public static ModelTensors parse(XContentParser parser) throws IOException {
         modelTensors.setStatusCode(statusCode);
         return modelTensors;
     }
+
+    @Override
+    public String toString() {
+        try {
+            return this.toXContent(JsonXContent.contentBuilder(), null).toString();
+        } catch (IOException e) {
+            throw new IllegalArgumentException("Can't convert ModelTensor to string", e);
+        }
+    }
 }

common/src/main/java/org/opensearch/ml/common/utils/StringUtils.java

@@ -35,6 +35,9 @@
 import org.json.JSONObject;
 import org.opensearch.OpenSearchParseException;
 import org.opensearch.action.ActionRequestValidationException;
+import org.opensearch.ml.common.output.model.ModelTensor;
+import org.opensearch.ml.common.output.model.ModelTensorOutput;
+import org.opensearch.ml.common.output.model.ModelTensors;
 
 import com.fasterxml.jackson.core.JsonProcessingException;
 import com.fasterxml.jackson.databind.JsonNode;
@@ -77,7 +80,6 @@ public class StringUtils {
 
     public static final String SAFE_INPUT_DESCRIPTION = "can only contain letters, numbers, spaces, and basic punctuation (.,!?():@-_'/\")";
 
-    public static final Gson gson = new Gson();
     public static final Gson PLAIN_NUMBER_GSON = new GsonBuilder()
         .serializeNulls()
         .registerTypeAdapter(Float.class, new PlainFloatAdapter())
@@ -86,6 +88,15 @@ public class StringUtils {
         .registerTypeAdapter(double.class, new PlainDoubleAdapter())
         .create();
 
+    public static final Gson gson;
+    static {
+        gson = new GsonBuilder()
+            .disableHtmlEscaping()
+            .registerTypeAdapter(ModelTensor.class, new ToStringTypeAdapter<>(ModelTensor.class))
+            .registerTypeAdapter(ModelTensorOutput.class, new ToStringTypeAdapter<>(ModelTensorOutput.class))
+            .registerTypeAdapter(ModelTensors.class, new ToStringTypeAdapter<>(ModelTensors.class))
+            .create();
+    }
     public static final String TO_STRING_FUNCTION_NAME = ".toString()";
 
     public static final ObjectMapper MAPPER = new ObjectMapper();

common/src/main/java/org/opensearch/ml/common/utils/ToStringTypeAdapter.java

@@ -0,0 +1,36 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package org.opensearch.ml.common.utils;
+
+import java.io.IOException;
+
+import com.google.gson.TypeAdapter;
+import com.google.gson.stream.JsonReader;
+import com.google.gson.stream.JsonWriter;
+
+public class ToStringTypeAdapter<T> extends TypeAdapter<T> {
+
+    private final Class<T> clazz;
+
+    public ToStringTypeAdapter(Class<T> clazz) {
+        this.clazz = clazz;
+    }
+
+    @Override
+    public void write(JsonWriter out, T value) throws IOException {
+        if (value == null) {
+            out.nullValue();
+            return;
+        }
+        String json = value.toString();
+        out.jsonValue(json);
+    }
+
+    @Override
+    public T read(JsonReader in) throws IOException {
+        throw new UnsupportedOperationException("Deserialization not supported");
+    }
+}

common/src/main/java/org/opensearch/ml/common/utils/ToolUtils.java

@@ -215,4 +215,38 @@ public static String getToolName(MLToolSpec toolSpec) {
         return toolSpec.getName() != null ? toolSpec.getName() : toolSpec.getType();
     }
 
+    /**
+     * Converts various types of tool output into a standardized ModelTensor format.
+     * The conversion logic depends on the type of input:
+     * <ul>
+     *     <li>For Map inputs: directly uses the map as data</li>
+     *     <li>For List inputs: wraps the list in a map with "output" as the key</li>
+     *     <li>For other types: converts to JSON string and attempts to parse as map,
+     *         if parsing fails, wraps the original output in a map with "output" as the key</li>
+     * </ul>
+     *
+     * @param output    The output object to be converted. Can be a Map, List, or any other object
+     * @param outputKey The key/name to be assigned to the resulting ModelTensor
+     * @return A ModelTensor containing the formatted output data
+     */
+    public static ModelTensor convertOutputToModelTensor(Object output, String outputKey) {
+        ModelTensor modelTensor;
+        if (output instanceof Map) {
+            modelTensor = ModelTensor.builder().name(outputKey).dataAsMap((Map) output).build();
+        } else if (output instanceof List) {
+            Map<String, Object> resultMap = new HashMap<>();
+            resultMap.put("output", output);
+            modelTensor = ModelTensor.builder().name(outputKey).dataAsMap(resultMap).build();
+        } else {
+            String outputJson = StringUtils.toJson(output);
+            Map<String, Object> resultMap;
+            if (StringUtils.isJson(outputJson)) {
+                resultMap = StringUtils.fromJson(outputJson, "output");
+            } else {
+                resultMap = Map.of("output", output);
+            }
+            modelTensor = ModelTensor.builder().name(outputKey).dataAsMap(resultMap).build();
+        }
+        return modelTensor;
+    }
 }

common/src/test/java/org/opensearch/ml/common/connector/HttpConnectorTest.java

@@ -304,6 +304,20 @@ public void parseResponse_NonJsonString() throws IOException {
         Assert.assertEquals("test output", modelTensors.get(0).getDataAsMap().get("response"));
     }
 
+    @Test
+    public void parseResponse_MapResponse() throws IOException {
+        HttpConnector connector = createHttpConnector();
+        Map<String, Object> responseMap = new HashMap<>();
+        responseMap.put("key1", "value1");
+        responseMap.put("key2", "value2");
+        List<ModelTensor> modelTensors = new ArrayList<>();
+
+        connector.parseResponse(responseMap, modelTensors, false);
+        Assert.assertEquals(1, modelTensors.size());
+        Assert.assertEquals("response", modelTensors.get(0).getName());
+        Assert.assertEquals(responseMap, modelTensors.get(0).getDataAsMap());
+    }
+
     @Test
     public void fillNullParameters() {
         HttpConnector connector = createHttpConnector();
@@ -442,4 +456,33 @@ public void parse_WithTenantId() throws IOException {
         Assert.assertEquals("test_tenant", connector.getTenantId());
     }
 
+    @Test
+    public void testParseResponse_MapResponse() throws IOException {
+        HttpConnector connector = createHttpConnector();
+
+        Map<String, Object> responseMap = new HashMap<>();
+        responseMap.put("result", "success");
+        responseMap.put("data", Arrays.asList("item1", "item2"));
+
+        List<ModelTensor> modelTensors = new ArrayList<>();
+        connector.parseResponse(responseMap, modelTensors, false);
+
+        Assert.assertEquals(1, modelTensors.size());
+        Assert.assertEquals("response", modelTensors.get(0).getName());
+        Assert.assertEquals(responseMap, modelTensors.get(0).getDataAsMap());
+    }
+
+    @Test
+    public void testParseResponse_NonStringNonMapResponse() throws IOException {
+        HttpConnector connector = createHttpConnector();
+
+        Integer numericResponse = 42;
+        List<ModelTensor> modelTensors = new ArrayList<>();
+        connector.parseResponse(numericResponse, modelTensors, false);
+
+        Assert.assertEquals(1, modelTensors.size());
+        Assert.assertEquals("response", modelTensors.get(0).getName());
+        Assert.assertEquals(42, modelTensors.get(0).getDataAsMap().get("response"));
+    }
+
 }

common/src/test/java/org/opensearch/ml/common/output/model/ModelTensorOutputTest.java

@@ -170,6 +170,14 @@ public void parse_SkipIrrelevantFields() throws IOException {
         assertArrayEquals(new long[] { 1, 3 }, modelTensor.getShape());
     }
 
+    @Test
+    public void test_ToString() {
+        String result = modelTensorOutput.toString();
+        String expected =
+            "{\"inference_results\":[{\"output\":[{\"name\":\"test\",\"data_type\":\"FLOAT32\",\"shape\":[1,3],\"data\":[1.0,2.0,3.0],\"byte_buffer\":{\"array\":\"AAEAAQ==\",\"order\":\"BIG_ENDIAN\"}}]}]}";
+        assertEquals(expected, result);
+    }
+
     private void readInputStream(ModelTensorOutput input, Consumer<ModelTensorOutput> verify) throws IOException {
         BytesStreamOutput bytesStreamOutput = new BytesStreamOutput();
         input.writeTo(bytesStreamOutput);

common/src/test/java/org/opensearch/ml/common/output/model/ModelTensorTest.java

@@ -6,6 +6,9 @@
 package org.opensearch.ml.common.output.model;
 
 import static org.junit.Assert.assertEquals;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.doThrow;
+import static org.mockito.Mockito.spy;
 import static org.opensearch.core.xcontent.ToXContent.EMPTY_PARAMS;
 
 import java.io.IOException;
@@ -122,4 +125,23 @@ public void test_NullDataType() {
             .byteBuffer(ByteBuffer.wrap(new byte[] { 0, 1, 0, 1 }))
             .build();
     }
+
+    @Test
+    public void test_ToString() {
+        String result = modelTensor.toString();
+        String expected =
+            "{\"name\":\"model_tensor\",\"data_type\":\"INT32\",\"shape\":[1,2,3],\"data\":[1,2,3],\"byte_buffer\":{\"array\":\"AAEAAQ==\",\"order\":\"BIG_ENDIAN\"},\"result\":\"test result\",\"dataAsMap\":{\"key1\":\"test value1\",\"key2\":\"test value2\"}}";
+        assertEquals(expected, result);
+    }
+
+    @Test
+    public void test_ToString_ThrowsException() throws IOException {
+        ModelTensor spyTensor = spy(modelTensor);
+        doThrow(new IOException("Mock IOException")).when(spyTensor).toXContent(any(XContentBuilder.class), any());
+
+        exceptionRule.expect(IllegalArgumentException.class);
+        exceptionRule.expectMessage("Can't convert ModelTensor to string");
+
+        spyTensor.toString();
+    }
 }

common/src/test/java/org/opensearch/ml/common/output/model/ModelTensorsTest.java

@@ -8,6 +8,9 @@
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.doThrow;
+import static org.mockito.Mockito.spy;
 import static org.opensearch.core.xcontent.ToXContent.EMPTY_PARAMS;
 
 import java.io.IOException;
@@ -274,4 +277,23 @@ public void parse_SkipIrrelevantFields() throws IOException {
         ModelTensor modelTensor = parsedTensors.getMlModelTensors().get(0);
         assertEquals("test_tensor", modelTensor.getName());
     }
+
+    @Test
+    public void test_ToString() {
+        String result = modelTensors.toString();
+        String expected =
+            "{\"output\":[{\"name\":\"model_tensor\",\"data_type\":\"INT32\",\"shape\":[1,2,3],\"data\":[1,2,3],\"byte_buffer\":{\"array\":\"AAEAAQ==\",\"order\":\"BIG_ENDIAN\"}}]}";
+        assertEquals(expected, result);
+    }
+
+    @Test
+    public void test_ToString_ThrowsException() throws IOException {
+        ModelTensors spyTensors = spy(modelTensors);
+        doThrow(new IOException("Mock IOException")).when(spyTensors).toXContent(any(XContentBuilder.class), any());
+
+        exceptionRule.expect(IllegalArgumentException.class);
+        exceptionRule.expectMessage("Can't convert ModelTensor to string");
+
+        spyTensors.toString();
+    }
 }

common/src/test/java/org/opensearch/ml/common/utils/StringUtilsTest.java

@@ -31,6 +31,10 @@
 import org.junit.Test;
 import org.opensearch.OpenSearchParseException;
 import org.opensearch.action.ActionRequestValidationException;
+import org.opensearch.ml.common.output.model.MLResultDataType;
+import org.opensearch.ml.common.output.model.ModelTensor;
+import org.opensearch.ml.common.output.model.ModelTensorOutput;
+import org.opensearch.ml.common.output.model.ModelTensors;
 
 import com.google.gson.JsonElement;
 import com.google.gson.TypeAdapter;
@@ -244,6 +248,48 @@ public void testGetErrorMessageWhenHiddenNull() {
      * in the values. Verifies that the method correctly extracts the prefixes of the toString()
      * method calls.
      */
+    @Test
+    public void testCollectToStringPrefixes() {
+        Map<String, String> map = new HashMap<>();
+        map.put("key1", "${parameters.tensor.toString()}");
+        map.put("key2", "${parameters.output.toString()}");
+        map.put("key3", "normal value");
+
+        List<String> prefixes = StringUtils.collectToStringPrefixes(map);
+
+        assertEquals(2, prefixes.size());
+        assertTrue(prefixes.contains("tensor"));
+        assertTrue(prefixes.contains("output"));
+    }
+
+    @Test
+    public void test_GsonTypeAdapters() {
+        // Test ModelTensor serialization
+        ModelTensor tensor = ModelTensor
+            .builder()
+            .name("test_tensor")
+            .data(new Number[] { 1, 2, 3 })
+            .dataType(MLResultDataType.INT32)
+            .build();
+
+        String tensorJson = StringUtils.gson.toJson(tensor);
+        assertEquals(tensor.toString(), tensorJson);
+
+        // Test ModelTensorOutput serialization
+        List<ModelTensors> outputs = new ArrayList<>();
+        outputs.add(ModelTensors.builder().mlModelTensors(Arrays.asList(tensor)).build());
+        ModelTensorOutput output = ModelTensorOutput.builder().mlModelOutputs(outputs).build();
+
+        String outputJson = StringUtils.gson.toJson(output);
+        assertEquals(output.toString(), outputJson);
+
+        // Test ModelTensors serialization
+        ModelTensors tensors = ModelTensors.builder().mlModelTensors(Arrays.asList(tensor)).build();
+
+        String tensorsJson = StringUtils.gson.toJson(tensors);
+        assertEquals(tensors.toString(), tensorsJson);
+    }
+
     @Test
     public void testGetToStringPrefix() {
         Map<String, String> parameters = new HashMap<>();