[ExceptionHandling] Throw proper 400 errors instead of 500 for agent execute and MCP (#3988) (#4051)

* improve exception handling



* feat: add test case for jsonparseexception



---------



(cherry picked from commit 943ef8c)

Signed-off-by: Pavan Yekbote <pybot@amazon.com>
Co-authored-by: Pavan Yekbote <pybot@amazon.com>
Co-authored-by: Dhrubo Saha <dhrubo@amazon.com>

Author: 3 people

common/src/main/java/org/opensearch/ml/common/MLCommonsClassLoader.java

@@ -28,6 +28,8 @@
 import org.opensearch.ml.common.output.MLOutputType;
 import org.reflections.Reflections;
 
+import com.fasterxml.jackson.core.JsonParseException;
+
 import lombok.extern.log4j.Log4j2;
 
 @Log4j2
@@ -255,16 +257,18 @@ public static boolean canInitMLInput(FunctionName functionName) {
         return mlInputClassMap.containsKey(functionName);
     }
 
-    public static <S> S initConnector(String name, Object[] initArgs, Class<?>... constructorParameterTypes) {
+    public static <S> S initConnector(String name, Object[] initArgs, Class<?>... constructorParameterTypes) throws JsonParseException {
         return init(connectorClassMap, name, initArgs, constructorParameterTypes);
     }
 
     @SuppressWarnings("unchecked")
-    public static <T extends Enum<T>, S> S initMLInput(T type, Object[] initArgs, Class<?>... constructorParameterTypes) {
+    public static <T extends Enum<T>, S> S initMLInput(T type, Object[] initArgs, Class<?>... constructorParameterTypes)
+        throws JsonParseException {
         return init(mlInputClassMap, type, initArgs, constructorParameterTypes);
     }
 
-    private static <T, S> S init(Map<T, Class<?>> map, T type, Object[] initArgs, Class<?>... constructorParameterTypes) {
+    private static <T, S> S init(Map<T, Class<?>> map, T type, Object[] initArgs, Class<?>... constructorParameterTypes)
+        throws JsonParseException {
         Class<?> clazz = map.get(type);
         if (clazz == null) {
             throw new IllegalArgumentException("Can't find class for type " + type);
@@ -278,6 +282,8 @@ private static <T, S> S init(Map<T, Class<?>> map, T type, Object[] initArgs, Cl
                 throw (MLException) cause;
             } else if (cause instanceof IllegalArgumentException) {
                 throw (IllegalArgumentException) cause;
+            } else if (cause instanceof JsonParseException) {
+                throw (JsonParseException) cause;
             } else {
                 log.error("Failed to init instance for type " + type, e);
                 return null;

common/src/test/java/org/opensearch/ml/common/MLCommonsClassLoaderTests.java

@@ -40,6 +40,8 @@
 import org.opensearch.ml.common.output.execute.samplecalculator.LocalSampleCalculatorOutput;
 import org.opensearch.search.SearchModule;
 
+import com.fasterxml.jackson.core.JsonParseException;
+
 public class MLCommonsClassLoaderTests {
 
     private SampleAlgoParams params;
@@ -183,14 +185,30 @@ public void testClassLoader_MLInput() throws IOException {
     }
 
     @Test(expected = IllegalArgumentException.class)
-    public void testConnectorInitializationException() {
+    public void testConnectorInitializationException() throws JsonParseException {
         // Example initialization parameters for connectors
         String initParam1 = "parameter1";
 
         // Initialize the first connector type
         MLCommonsClassLoader.initConnector("Connector", new Object[] { initParam1 }, String.class);
     }
 
+    @Test(expected = JsonParseException.class)
+    public void testInitMLInput_JsonParseException() throws IOException {
+        String invalidJsonStr = "invalid-json";
+        XContentParser parser = XContentType.JSON
+            .xContent()
+            .createParser(
+                new NamedXContentRegistry(new SearchModule(Settings.EMPTY, Collections.emptyList()).getNamedXContents()),
+                null,
+                invalidJsonStr
+            );
+        parser.nextToken();
+
+        MLCommonsClassLoader
+            .initMLInput(FunctionName.AGENT, new Object[] { parser, FunctionName.AGENT }, XContentParser.class, FunctionName.class);
+    }
+
     public enum TestEnum {
         TEST
     }

plugin/src/main/java/org/opensearch/ml/action/mcpserver/TransportMcpToolsRegisterAction.java

@@ -115,7 +115,7 @@ protected void doExecute(Task task, ActionRequest request, ActionListener<MLMcpT
                         String exceptionMessage = String
                             .format(Locale.ROOT, "Unable to register tools: %s as they already exist", existingTools);
                         log.warn(exceptionMessage);
-                        restoreListener.onFailure(new OpenSearchException(exceptionMessage));
+                        restoreListener.onFailure(new IllegalArgumentException(exceptionMessage));
                     } else {
                         indexMcpTools(registerNodesRequest, restoreListener);
                     }