[gpt-oss][1][bugfix] fix streaming final output (#24466)

Signed-off-by: Andrew Xia <axia@meta.com>

tests/entrypoints/openai/test_response_api_with_harmony.py

@@ -364,6 +364,8 @@ async def test_streaming(client: OpenAI, model_name: str, background: bool):
             events.append(event)
 
         assert len(events) > 0
+        response_completed_event = events[-1]
+        assert len(response_completed_event.response.output) > 0
 
         if background:
             starting_after = 5

tests/entrypoints/test_context.py

@@ -4,7 +4,7 @@
 from unittest.mock import MagicMock, patch
 
 import pytest
-from openai_harmony import StreamState
+from openai_harmony import Author, Message, Role, StreamState, TextContent
 
 from vllm.entrypoints.context import HarmonyContext, StreamingHarmonyContext
 from vllm.outputs import CompletionOutput, RequestOutput
@@ -423,3 +423,78 @@ async def test_streaming_multi_turn_token_counting(mock_parser):
     additional_tool_tokens = 13 - 8 - 3  # = 2
     assert context.num_tool_output_tokens == expected_tool_tokens \
         + additional_tool_tokens
+
+
+@pytest.mark.asyncio
+async def test_streaming_message_synchronization(mock_parser):
+    """Test message synchronization logic from lines 413-417 in context.py.
+
+    This test verifies that when parser.messages contains more messages than
+    the context's _messages (minus initial messages), the context properly
+    extends its message list with the new parser messages.
+    """
+
+    # Create a streaming context with some initial messages
+    initial_messages = [
+        Message(
+            author=Author(role=Role.USER, name="user"),
+            content=[TextContent(text="Hello")],
+            recipient=Role.ASSISTANT,
+        )
+    ]
+    context = StreamingHarmonyContext(messages=initial_messages,
+                                      available_tools=[])
+
+    # Verify initial state
+    assert len(context._messages) == 1
+    assert context.num_init_messages == 1
+
+    # Mock parser to have more messages than context
+    # Simulate parser having processed 3 new messages
+    mock_parser.messages = [
+        Message(
+            author=Author(role=Role.ASSISTANT, name="assistant"),
+            content=[TextContent(text="Response 1")],
+            recipient=Role.USER,
+        ),
+    ]
+
+    # This should trigger the message synchronization logic
+    context.append_output(
+        create_mock_request_output(prompt_token_ids=[1, 2, 3],
+                                   output_token_ids=[101],
+                                   finished=False))
+
+    # Verify that messages were synchronized
+    assert len(context._messages) == 2
+
+    # Verify the new messages were added correctly
+    assert context._messages[1].content[0].text == "Response 1"
+
+    # Test the specific condition from line 413-414:
+    # len(self._messages) - self.num_init_messages < len(self.parser.messages)
+    messages_minus_init = len(context._messages) - context.num_init_messages
+    parser_messages_count = len(mock_parser.messages)
+
+    # After synchronization, they should be equal (no longer less than)
+    assert messages_minus_init == parser_messages_count
+
+    # Test edge case: add one more parser message
+    mock_parser.messages.append(
+        Message(
+            author=Author(role=Role.ASSISTANT, name="assistant"),
+            content=[TextContent(text="Response 4")],
+            recipient=Role.USER,
+        ))
+
+    # Create another output to trigger synchronization again
+    mock_output2 = create_mock_request_output(prompt_token_ids=[1, 2, 3],
+                                              output_token_ids=[102],
+                                              finished=True)
+
+    context.append_output(mock_output2)
+
+    # Verify the fourth message was added, num_init_messages is still 1
+    assert len(context._messages) == 3
+    assert context.num_init_messages == 1
+    assert context._messages[2].content[0].text == "Response 4"

vllm/entrypoints/context.py

@@ -151,6 +151,9 @@ class HarmonyContext(ConversationContext):
             self._update_decode_token_usage(output)
             # Move current turn to previous turn for next turn's calculations
             self.previous_turn = self.current_turn.copy()
+            # append_output is called only once before tool calling
+            # in non-streaming case
+            # so we can append all the parser messages to _messages
             output_msgs = self.parser.messages
             # The responses finish reason is set in the last message
             self.finish_reason = output.outputs[0].finish_reason
@@ -387,7 +390,7 @@ class StreamingHarmonyContext(HarmonyContext):
 
     @property
     def messages(self) -> list:
-        return self.parser.messages
+        return self._messages
 
     def append_output(self, output: Union[RequestOutput,
                                           list[Message]]) -> None:
@@ -412,6 +415,11 @@ class StreamingHarmonyContext(HarmonyContext):
             # Check if the current token is part of reasoning content
             self._update_num_reasoning_tokens()
             self.last_tok = tok
+            if len(self._messages) - self.num_init_messages < len(
+                    self.parser.messages):
+                self._messages.extend(
+                    self.parser.messages[len(self._messages) -
+                                         self.num_init_messages:])
         else:
             # Handle the case of tool output in direct message format
             assert len(output) == 1, "Tool output should be a single message"
@@ -424,6 +432,7 @@ class StreamingHarmonyContext(HarmonyContext):
             for tok in toks:
                 self.parser.process(tok)
             self.last_tok = toks[-1]
+            # TODO: add tool_output messages to self._messages
 
     def is_expecting_start(self) -> bool:
         return self.parser.state == StreamState.EXPECT_START