fix(adk-middleware): "SecuritySchemeType is not JSON serializable" (#1332)

* fix(adk-middleware): "SecuritySchemeType is not JSON serializable"

this solves the issue of the built-in `adk_request_credentials` function call failing with

```
Traceback (most recent call last):
  File "/Users/joar.wandborg/git/myproject/.venv/lib/python3.14/site-packages/ag_ui_adk/adk_agent.py", line 2132, in _run_adk_in_background
    async for ag_ui_event in event_translator.translate_lro_function_calls(
    ...<5 lines>...
        logger.debug(f"Event queued: {type(ag_ui_event).__name__} (thread {input.thread_id}, queue size after: {event_queue.qsize()})")
  File "/Users/joar.wandborg/git/myproject/.venv/lib/python3.14/site-packages/ag_ui_adk/event_translator.py", line 763, in translate_lro_function_calls
    args_str = json.dumps(long_running_function_call.args) if isinstance(long_running_function_call.args, dict) else str(long_running_function_call.args)
               ~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/joar.wandborg/.local/share/uv/python/cpython-3.14.3-macos-aarch64-none/lib/python3.14/json/__init__.py", line 235, in dumps
    return _default_encoder.encode(obj)
           ~~~~~~~~~~~~~~~~~~~~~~~^^^^^
  File "/Users/joar.wandborg/.local/share/uv/python/cpython-3.14.3-macos-aarch64-none/lib/python3.14/json/encoder.py", line 202, in encode
    chunks = self.iterencode(o, _one_shot=True)
  File "/Users/joar.wandborg/.local/share/uv/python/cpython-3.14.3-macos-aarch64-none/lib/python3.14/json/encoder.py", line 263, in iterencode
    return _iterencode(o, 0)
  File "/Users/joar.wandborg/.local/share/uv/python/cpython-3.14.3-macos-aarch64-none/lib/python3.14/json/encoder.py", line 182, in default
    raise TypeError(f'Object of type {o.__class__.__name__} '
                    f'is not JSON serializable')
TypeError: Object of type SecuritySchemeType is not JSON serializable
```

* refactor(adk-middleware): introduce serialize_tool_args for JSON serialization

Added a new utility function `serialize_tool_args` to handle JSON serialization of tool-call arguments, addressing issues with non-standard types like Pydantic models and Enums. Updated relevant code in `client_proxy_tool`, `event_translator`, and `converters` to utilize this new function, ensuring consistent serialization across the application. Added comprehensive tests for the new serialization functionality.

---------

Co-authored-by: Mark <mark@contextable.com>

Author: joar

integrations/adk-middleware/python/src/ag_ui_adk/client_proxy_tool.py

@@ -20,6 +20,7 @@
 )
 
 from .config import PredictStateMapping
+from .serialization import serialize_tool_args
 
 logger = logging.getLogger(__name__)
 
@@ -241,7 +242,7 @@ async def _execute_proxy_tool(self, args: Dict[str, Any], tool_context: Any) ->
             logger.debug(f"Emitted TOOL_CALL_START for {tool_call_id}")
 
             # Emit TOOL_CALL_ARGS event
-            args_json = json.dumps(args)
+            args_json = serialize_tool_args(args)
             args_event = ToolCallArgsEvent(
                 type=EventType.TOOL_CALL_ARGS,
                 tool_call_id=tool_call_id,

integrations/adk-middleware/python/src/ag_ui_adk/event_translator.py

@@ -23,6 +23,7 @@
 from google.adk.events import Event as ADKEvent
 
 from .config import PredictStateMapping, normalize_predict_state
+from .serialization import serialize_tool_args
 
 import logging
 logger = logging.getLogger(__name__)
@@ -761,9 +762,7 @@ async def translate_lro_function_calls(self,adk_event: ADKEvent)-> AsyncGenerato
                             parent_message_id=None
                         )
                         if hasattr(fc, 'args') and fc.args:
-                            # Convert args to string (JSON format)
-                            import json
-                            args_str = json.dumps(fc.args) if isinstance(fc.args, dict) else str(fc.args)
+                            args_str = serialize_tool_args(fc.args)
                             yield ToolCallArgsEvent(
                                 type=EventType.TOOL_CALL_ARGS,
                                 tool_call_id=fc.id,
@@ -839,8 +838,7 @@ async def _translate_function_calls(
 
             # Emit TOOL_CALL_ARGS if we have arguments
             if hasattr(func_call, 'args') and func_call.args:
-                # Convert args to string (JSON format)
-                args_str = json.dumps(func_call.args) if isinstance(func_call.args, dict) else str(func_call.args)
+                args_str = serialize_tool_args(func_call.args)
 
                 yield ToolCallArgsEvent(
                     type=EventType.TOOL_CALL_ARGS,
@@ -1198,7 +1196,7 @@ def _translate_function_calls_to_tool_calls(function_calls: List[Any]) -> List[T
             type="function",
             function=FunctionCall(
                 name=fc.name,
-                arguments=json.dumps(fc.args) if hasattr(fc, 'args') and fc.args else "{}"
+                arguments=serialize_tool_args(fc.args) if hasattr(fc, 'args') and fc.args else "{}"
             )
         )
         tool_calls.append(tool_call)

integrations/adk-middleware/python/src/ag_ui_adk/serialization.py

@@ -0,0 +1,30 @@
+"""Shared JSON serialization helpers for tool-call arguments.
+
+Standard ``json.dumps`` fails when args dicts contain Pydantic models or
+Python ``Enum`` values (e.g. ``SecuritySchemeType``).  The helper here uses
+Pydantic's ``TypeAdapter`` which knows how to serialize those types.
+"""
+
+from __future__ import annotations
+
+from typing import Any
+
+from pydantic import TypeAdapter
+
+_dict_adapter: TypeAdapter[dict[str, Any]] = TypeAdapter(dict[str, Any])
+
+
+def serialize_tool_args(args: Any) -> str:
+    """Serialize tool-call *args* to a JSON string.
+
+    Handles dicts that may contain Pydantic models, Enums, or other
+    non-stdlib-serializable values by delegating to Pydantic's
+    ``TypeAdapter.dump_json``.
+
+    Returns:
+        A JSON-encoded string.  For non-dict values the result is
+        ``str(args)``.
+    """
+    if isinstance(args, dict):
+        return _dict_adapter.dump_json(args).decode()
+    return str(args)

integrations/adk-middleware/python/src/ag_ui_adk/utils/converters.py

@@ -15,6 +15,8 @@
 from google.adk.events import Event as ADKEvent
 from google.genai import types
 
+from ..serialization import serialize_tool_args
+
 logger = logging.getLogger(__name__)
 
 def _get_text_value(item: Union[dict, TextInputContent]) -> Optional[str]:
@@ -234,7 +236,7 @@ def convert_adk_event_to_ag_ui_message(event: ADKEvent) -> Optional[Message]:
                         type="function",
                         function=FunctionCall(
                             name=part.function_call.name,
-                            arguments=json.dumps(part.function_call.args) if hasattr(part.function_call, 'args') else "{}"
+                            arguments=serialize_tool_args(part.function_call.args) if hasattr(part.function_call, 'args') else "{}"
                         )
                     ))
 

integrations/adk-middleware/python/tests/test_event_translator_comprehensive.py

@@ -766,7 +766,7 @@ async def test_translate_function_calls_basic(self, translator, mock_adk_event):
         assert events[0].tool_call_id == "call_123"
         assert events[0].tool_call_name == "test_function"
         assert events[1].tool_call_id == "call_123"
-        assert events[1].delta == '{"param1": "value1"}'
+        assert json.loads(events[1].delta) == {"param1": "value1"}
         assert events[2].tool_call_id == "call_123"
 
     @pytest.mark.asyncio

integrations/adk-middleware/python/tests/test_lro_sse_id_remap.py

@@ -17,6 +17,7 @@
 """
 
 import asyncio
+import json
 import os
 import uuid
 import warnings
@@ -276,6 +277,85 @@ async def test_lro_emitted_ids_cleared_on_reset(self, translator):
         translator.reset()
         assert translator.lro_emitted_ids_by_name == {}
 
+    @pytest.mark.asyncio
+    async def test_lro_adk_request_credential_oauth2(self, translator):
+        """Regression (#1331): adk_request_credential with OAuth2 AuthConfig must serialize.
+
+        ADK emits a long-running function call named ``adk_request_credential``
+        whose args dict contains an ``AuthConfig`` Pydantic model.  The model
+        in turn nests ``OAuth2`` which has a ``type_: SecuritySchemeType`` enum
+        field.  Before the fix, ``json.dumps`` raised:
+
+            TypeError: Object of type SecuritySchemeType is not JSON serializable
+        """
+        from fastapi.openapi.models import OAuthFlowAuthorizationCode
+        from google.adk.auth.auth_schemes import OAuth2, OAuthFlows, SecuritySchemeType
+        from google.adk.auth import AuthConfig
+        from google.adk.auth.auth_credential import (
+            AuthCredential,
+            AuthCredentialTypes,
+            OAuth2Auth,
+        )
+
+        auth_scheme = OAuth2(
+            flows=OAuthFlows(
+                authorizationCode=OAuthFlowAuthorizationCode(
+                    authorizationUrl="https://accounts.google.com/o/oauth2/auth",
+                    tokenUrl="https://oauth2.googleapis.com/token",
+                    scopes={
+                        "https://www.googleapis.com/auth/calendar": "Calendar access",
+                    },
+                ),
+            ),
+        )
+        raw_credential = AuthCredential(
+            auth_type=AuthCredentialTypes.OAUTH2,
+            oauth2=OAuth2Auth(
+                client_id="123456.apps.googleusercontent.com",
+                client_secret="GOCSPX-secret",
+            ),
+        )
+        auth_config = AuthConfig(
+            auth_scheme=auth_scheme,
+            raw_auth_credential=raw_credential,
+        )
+
+        fc = MagicMock()
+        fc.id = "adk-cred-123"
+        fc.name = "adk_request_credential"
+        fc.args = {
+            "function_call_id": "adk-cred-123",
+            "auth_config": auth_config,
+        }
+        part = MagicMock()
+        part.function_call = fc
+        part.text = None
+        evt = MagicMock()
+        evt.content = MagicMock()
+        evt.content.parts = [part]
+        evt.long_running_tool_ids = ["adk-cred-123"]
+
+        events = []
+        async for e in translator.translate_lro_function_calls(evt):
+            events.append(e)
+
+        assert len(events) == 3
+        assert events[0].type == EventType.TOOL_CALL_START
+        assert events[0].tool_call_name == "adk_request_credential"
+
+        args_event = events[1]
+        assert args_event.type == EventType.TOOL_CALL_ARGS
+        parsed = json.loads(args_event.delta)
+        assert parsed["function_call_id"] == "adk-cred-123"
+
+        ac = parsed["auth_config"]
+        assert ac["auth_scheme"]["type_"] == "oauth2"
+        assert ac["raw_auth_credential"]["auth_type"] == "oauth2"
+        assert ac["raw_auth_credential"]["oauth2"]["client_id"] == "123456.apps.googleusercontent.com"
+        auth_code_flow = ac["auth_scheme"]["flows"]["authorizationCode"]
+        assert auth_code_flow["authorizationUrl"] == "https://accounts.google.com/o/oauth2/auth"
+        assert auth_code_flow["tokenUrl"] == "https://oauth2.googleapis.com/token"
+
     @pytest.mark.asyncio
     async def test_parallel_same_name_lro_calls_all_emitted(self, translator):
         """Multiple parallel LRO calls to the same tool should all be emitted (issue #1334)."""
@@ -1169,4 +1249,4 @@ def no_streaming_config(inp):
     else:
         print("No Google authentication — running unit tests only")
         print("Set GOOGLE_API_KEY or configure Vertex AI to run integration tests")
-        pytest.main([__file__, "-v", "-s", "-k", "not Integration"])
+        pytest.main([__file__, "-v", "-s", "-k", "not Integration"])

integrations/adk-middleware/python/tests/test_serialization.py

@@ -0,0 +1,73 @@
+"""Tests for the shared serialize_tool_args helper.
+
+Covers plain dicts, dicts containing Python Enums (the SecuritySchemeType
+scenario), dicts containing Pydantic models, non-dict values, and edge cases.
+"""
+
+import enum
+import json
+
+from pydantic import BaseModel
+
+from ag_ui_adk.serialization import serialize_tool_args
+
+
+class FakeSecuritySchemeType(enum.Enum):
+    oauth2 = "oauth2"
+    apiKey = "apiKey"
+
+
+class NestedModel(BaseModel):
+    url: str
+    scheme_type: FakeSecuritySchemeType
+
+
+class TestSerializeToolArgs:
+
+    def test_plain_dict(self):
+        args = {"city": "Seattle", "units": "metric"}
+        result = serialize_tool_args(args)
+        assert json.loads(result) == args
+
+    def test_dict_with_enum_value(self):
+        """Regression (#1331): SecuritySchemeType-like enums must not raise TypeError."""
+        args = {
+            "auth_type": FakeSecuritySchemeType.oauth2,
+            "scopes": ["read", "write"],
+        }
+        result = serialize_tool_args(args)
+        parsed = json.loads(result)
+        assert parsed["auth_type"] == "oauth2"
+        assert parsed["scopes"] == ["read", "write"]
+
+    def test_dict_with_pydantic_model_value(self):
+        args = {
+            "endpoint": NestedModel(
+                url="https://example.com",
+                scheme_type=FakeSecuritySchemeType.apiKey,
+            )
+        }
+        result = serialize_tool_args(args)
+        parsed = json.loads(result)
+        assert parsed["endpoint"]["url"] == "https://example.com"
+        assert parsed["endpoint"]["scheme_type"] == "apiKey"
+
+    def test_dict_with_nested_enum(self):
+        args = {
+            "config": {
+                "type": FakeSecuritySchemeType.oauth2,
+                "enabled": True,
+            }
+        }
+        result = serialize_tool_args(args)
+        parsed = json.loads(result)
+        assert parsed["config"]["type"] == "oauth2"
+
+    def test_string_args_passthrough(self):
+        assert serialize_tool_args("raw_string") == "raw_string"
+
+    def test_non_dict_non_string(self):
+        assert serialize_tool_args(42) == "42"
+
+    def test_empty_dict(self):
+        assert serialize_tool_args({}) == "{}"

integrations/adk-middleware/python/tests/test_utils_converters.py

@@ -399,7 +399,7 @@ def test_convert_assistant_event_with_function_call(self):
         assert tool_call.id == "call_123"
         assert tool_call.type == "function"
         assert tool_call.function.name == "get_weather"
-        assert tool_call.function.arguments == '{"location": "Boston"}'
+        assert json.loads(tool_call.function.arguments) == {"location": "Boston"}
 
     def test_convert_assistant_event_with_text_and_function_call(self):
         """Test converting assistant event with both text and function call."""