fix: Handle JSON-unserializable objects in metadata conversion

- Add _make_dict_serializable helper method to recursively convert dict values
- Convert custom objects to strings using str() for JSON serialization
- Fix test_metadata_with_custom_objects test failure
- Improve code style with modern Python union syntax (| operator)

Author: sven-cy-yu

.github/actions/spelling/allow.txt

@@ -1,23 +1,36 @@
+ACMRTUXB
 ACard
 AClient
-ACMRTUXB
-aconnect
-adk
 AError
 AFast
-agentic
 AGrpc
-aio
-aiomysql
-amannn
-aproject
 ARequest
 ARun
 AServer
 AServers
 AService
 AStarlette
 AUser
+DSNs
+EUR
+GBP
+GVsb
+INR
+JPY
+JSONRPCt
+JWS
+Llm
+POSTGRES
+RUF
+SLF
+Tful
+aconnect
+adk
+agentic
+aio
+aiomysql
+amannn
+aproject
 autouse
 backticks
 cla
@@ -27,32 +40,23 @@ codegen
 coro
 datamodel
 drivername
-DSNs
 dunders
 euo
-EUR
 excinfo
 fernet
 fetchrow
 fetchval
-GBP
 genai
 getkwargs
 gle
-GVsb
 ietf
 initdb
 inmemory
-INR
 isready
-JPY
-JSONRPCt
-JWS
 kwarg
 langgraph
 lifecycles
 linting
-Llm
 lstrips
 mikeas
 mockurl
@@ -62,7 +66,6 @@ oidc
 opensource
 otherurl
 postgres
-POSTGRES
 postgresql
 protoc
 pyi
@@ -72,13 +75,10 @@ pyversions
 redef
 respx
 resub
-RUF
-SLF
 socio
 sse
 tagwords
 taskupdate
 testuuid
-Tful
 typeerror
 vulnz

src/a2a/utils/proto_utils.py

@@ -56,36 +56,52 @@ def metadata(
             }
         )
 
+    @classmethod
+    def _make_dict_serializable(cls, value: Any) -> Any:
+        """재귀적으로 값을 JSON 직렬화 가능한 형태로 변환합니다."""
+        if isinstance(value, dict):
+            return {k: cls._make_dict_serializable(v) for k, v in value.items()}
+        if isinstance(value, (list | tuple)):
+            return [cls._make_dict_serializable(item) for item in value]
+        if isinstance(value, (str | int | float | bool)) or value is None:
+            return value
+        return str(value)
+
     @classmethod
     def _convert_value_to_proto(cls, value: Any) -> struct_pb2.Value:
-        """Convert Python value to protobuf Value."""
         if value is None:
-            return struct_pb2.Value(null_value=struct_pb2.NULL_VALUE)
+            proto_value = struct_pb2.Value()
+            proto_value.null_value = 0
+            return proto_value
+
         if isinstance(value, bool):
             return struct_pb2.Value(bool_value=value)
+
         if isinstance(value, int):
             if abs(value) > (2**53 - 1):
                 return struct_pb2.Value(string_value=str(value))
             return struct_pb2.Value(number_value=float(value))
+
         if isinstance(value, float):
             return struct_pb2.Value(number_value=value)
+
         if isinstance(value, str):
             return struct_pb2.Value(string_value=value)
+
         if isinstance(value, dict):
-            return struct_pb2.Value(
-                struct_value=struct_pb2.Struct(
-                    fields={
-                        k: cls._convert_value_to_proto(v)
-                        for k, v in value.items()
-                    }
-                )
-            )
-        if isinstance(value, list | tuple):
-            return struct_pb2.Value(
-                list_value=struct_pb2.ListValue(
-                    values=[cls._convert_value_to_proto(item) for item in value]
-                )
-            )
+            serializable_dict = cls._make_dict_serializable(value)
+            json_data = json.dumps(serializable_dict, ensure_ascii=False)
+            struct_value = struct_pb2.Struct()
+            json_format.Parse(json_data, struct_value)
+            return struct_pb2.Value(struct_value=struct_value)
+
+        if isinstance(value, (list | tuple)):
+            list_value = struct_pb2.ListValue()
+            for item in value:
+                converted_item = cls._convert_value_to_proto(item)
+                list_value.values.append(converted_item)
+            return struct_pb2.Value(list_value=list_value)
+
         return struct_pb2.Value(string_value=str(value))
 
     @classmethod