[responsesAPI][bugfix] serialize harmony messages (#26185)

Signed-off-by: Andrew Xia <axia@meta.com>
Co-authored-by: Ye (Charlotte) Qi <yeq@meta.com>

tests/entrypoints/openai/test_response_api_with_harmony.py

@@ -8,6 +8,9 @@ import pytest
 import pytest_asyncio
 import requests
 from openai import BadRequestError, NotFoundError, OpenAI
+from openai_harmony import (
+    Message,
+)
 
 from ...utils import RemoteOpenAIServer
 
@@ -326,6 +329,7 @@ async def test_streaming(client: OpenAI, model_name: str, background: bool):
             ],
             stream=True,
             background=background,
+            extra_body={"enable_response_messages": True},
         )
 
         current_item_id = ""
@@ -334,6 +338,7 @@ async def test_streaming(client: OpenAI, model_name: str, background: bool):
         events = []
         current_event_mode = None
         resp_id = None
+        checked_response_completed = False
         async for event in response:
             if event.type == "response.created":
                 resp_id = event.response.id
@@ -346,6 +351,16 @@ async def test_streaming(client: OpenAI, model_name: str, background: bool):
             ]:
                 assert "input_messages" in event.response.model_extra
                 assert "output_messages" in event.response.model_extra
+                if event.type == "response.completed":
+                    # make sure the serialization of content works
+                    for msg in event.response.model_extra["output_messages"]:
+                        # make sure we can convert the messages back into harmony
+                        Message.from_dict(msg)
+
+                    for msg in event.response.model_extra["input_messages"]:
+                        # make sure we can convert the messages back into harmony
+                        Message.from_dict(msg)
+                    checked_response_completed = True
 
             if current_event_mode != event.type:
                 current_event_mode = event.type
@@ -390,6 +405,7 @@ async def test_streaming(client: OpenAI, model_name: str, background: bool):
         assert len(events) > 0
         response_completed_event = events[-1]
         assert len(response_completed_event.response.output) > 0
+        assert checked_response_completed
 
         if background:
             starting_after = 5

vllm/entrypoints/openai/protocol.py

@@ -63,6 +63,7 @@ from pydantic import (
     Field,
     TypeAdapter,
     ValidationInfo,
+    field_serializer,
     field_validator,
     model_validator,
 )
@@ -2078,11 +2079,6 @@ class ResponsesResponse(OpenAIBaseModel):
     model: str
     object: Literal["response"] = "response"
     output: list[ResponseOutputItem]
-    # These are populated when enable_response_messages is set to True
-    # TODO: Currently an issue where content of harmony messages
-    # is not available when these are serialized. Metadata is available
-    input_messages: Optional[list[ChatCompletionMessageParam]] = None
-    output_messages: Optional[list[ChatCompletionMessageParam]] = None
     parallel_tool_calls: bool
     temperature: float
     tool_choice: ToolChoice
@@ -2102,6 +2098,49 @@ class ResponsesResponse(OpenAIBaseModel):
     usage: Optional[ResponseUsage] = None
     user: Optional[str] = None
 
+    # --8<-- [start:responses-extra-params]
+    # These are populated when enable_response_messages is set to True
+    # NOTE: custom serialization is needed
+    # see serialize_input_messages and serialize_output_messages
+    input_messages: Optional[list[ChatCompletionMessageParam]] = None
+    output_messages: Optional[list[ChatCompletionMessageParam]] = None
+    # --8<-- [end:responses-extra-params]
+
+    # NOTE: openAI harmony doesn't serialize TextContent properly,
+    # TODO: this fixes for TextContent, but need to verify for tools etc
+    # https://github.com/openai/harmony/issues/78
+    @field_serializer("output_messages", when_used="json")
+    def serialize_output_messages(self, msgs, _info):
+        if msgs:
+            serialized = []
+            for m in msgs:
+                if isinstance(m, dict):
+                    serialized.append(m)
+                elif hasattr(m, "__dict__"):
+                    serialized.append(m.to_dict())
+                else:
+                    # fallback to pyandic dump
+                    serialized.append(m.model_dump_json())
+            return serialized
+        return None
+
+    # NOTE: openAI harmony doesn't serialize TextContent properly, this fixes it
+    # https://github.com/openai/harmony/issues/78
+    @field_serializer("input_messages", when_used="json")
+    def serialize_input_messages(self, msgs, _info):
+        if msgs:
+            serialized = []
+            for m in msgs:
+                if isinstance(m, dict):
+                    serialized.append(m)
+                elif hasattr(m, "__dict__"):
+                    serialized.append(m.to_dict())
+                else:
+                    # fallback to pyandic dump
+                    serialized.append(m.model_dump_json())
+            return serialized
+        return None
+
     @classmethod
     def from_request(
         cls,

vllm/entrypoints/openai/serving_responses.py

@@ -1876,6 +1876,6 @@ class OpenAIServingResponses(OpenAIServing):
                 ResponseCompletedEvent(
                     type="response.completed",
                     sequence_number=-1,
-                    response=final_response.model_dump(),
+                    response=final_response,
                 )
             )