Fix Responses API streaming for multiple auto tool calls (#39626)

Signed-off-by: noobhappylife <aratar1991@hotmail.com>

tests/entrypoints/openai/responses/test_function_call.py

@@ -249,40 +249,74 @@ async def test_function_calling_with_streaming_expected_arguments(
                 "additionalProperties": False,
             },
             "strict": True,
-        }
+        },
+        {
+            "type": "function",
+            "name": "get_time",
+            "description": "Get current local time for provided location.",
+            "parameters": {
+                "type": "object",
+                "properties": {
+                    "location": {"type": "string"},
+                },
+                "required": ["location"],
+                "additionalProperties": False,
+            },
+            "strict": True,
+        },
     ]
 
     stream_response = await client.responses.create(
         model=model_name,
-        input="Can you tell me what the current weather is in Berlin?",
+        input=(
+            "Use tools only. Call get_weather for Berlin and get_time for Tokyo. "
+            "Do not answer directly."
+        ),
         tools=tools,
         stream=True,
     )
 
-    tool_call_item = None
-    completed_event = None
+    tool_call_items = {}
+    arguments_done_events = {}
+    completed_events = {}
     async for event in stream_response:
         if (
             event.type == "response.output_item.added"
             and event.item.type == "function_call"
         ):
-            tool_call_item = event.item
-        elif event.type == "response.function_call_arguments.delta" and tool_call_item:
+            tool_call_items[event.output_index] = event.item
+        elif event.type == "response.function_call_arguments.delta":
+            tool_call_item = tool_call_items[event.output_index]
             tool_call_item.arguments += event.delta
+        elif event.type == "response.function_call_arguments.done":
+            arguments_done_events[event.output_index] = event
         elif (
             event.type == "response.output_item.done"
             and event.item.type == "function_call"
         ):
-            completed_event = event
-    assert tool_call_item is not None
-    assert tool_call_item.type == "function_call"
-    assert tool_call_item.name == "get_weather"
-    assert completed_event is not None
-    assert tool_call_item.arguments == completed_event.item.arguments
-    assert tool_call_item.name == completed_event.item.name
-    args = json.loads(tool_call_item.arguments)
-    assert "location" in args
-    assert args["location"] is not None
+            completed_events[event.output_index] = event
+    assert len(tool_call_items) >= 2
+    assert len(arguments_done_events) >= 2
+    assert len(completed_events) >= 2
+
+    tool_calls_by_name = {
+        event.item.name: (
+            tool_call_items[output_index],
+            arguments_done_events[output_index],
+            event.item,
+        )
+        for output_index, event in completed_events.items()
+    }
+    assert {"get_weather", "get_time"}.issubset(tool_calls_by_name)
+    for added_item, arguments_done_event, completed_item in tool_calls_by_name.values():
+        assert added_item.type == "function_call"
+        assert added_item.arguments == arguments_done_event.arguments
+        assert added_item.arguments == completed_item.arguments
+        assert added_item.name == arguments_done_event.name
+        assert added_item.name == completed_item.name
+        args = json.loads(added_item.arguments)
+        assert "location" in args
+        assert args["location"] is not None
 
 
 @pytest.mark.asyncio

tests/entrypoints/openai/responses/test_serving_responses.py

@@ -27,7 +27,9 @@ from openai.types.responses.tool import (
 import vllm.envs as envs
 from vllm.entrypoints.mcp.tool_server import ToolServer
 from vllm.entrypoints.openai.engine.protocol import (
+    DeltaFunctionCall,
     DeltaMessage,
+    DeltaToolCall,
     ErrorResponse,
     RequestResponseMetadata,
 )
@@ -928,3 +930,197 @@ class TestStreamingReasoningToContentTransition:
         ]
         assert len(item_done_events) == 1
         assert isinstance(item_done_events[0].item, ResponseReasoningItem)
+
+
+class TestAutoToolStreaming:
+    @staticmethod
+    async def _collect_events(delta_sequence: list[DeltaMessage]):
+        serving = _make_serving_instance_with_reasoning()
+        _mock_parser_with_reasoning(serving, delta_sequence)
+
+        contexts = [
+            _make_simple_context_with_output("chunk", [i])
+            for i in range(len(delta_sequence))
+        ]
+
+        async def result_generator():
+            for ctx in contexts:
+                yield ctx
+
+        request = ResponsesRequest(
+            input="hi",
+            tools=[
+                {
+                    "type": "function",
+                    "name": "get_weather",
+                    "description": "Get weather.",
+                    "parameters": {
+                        "type": "object",
+                        "properties": {"location": {"type": "string"}},
+                        "required": ["location"],
+                        "additionalProperties": False,
+                    },
+                }
+            ],
+            tool_choice="auto",
+            stream=True,
+        )
+        sampling_params = SamplingParams(max_tokens=64)
+        metadata = RequestResponseMetadata(request_id="req")
+        _identity_increment._counter = 0  # type: ignore
+
+        events = []
+        async for event in serving._process_simple_streaming_events(
+            request=request,
+            sampling_params=sampling_params,
+            result_generator=result_generator(),
+            context=SimpleContext(),
+            model_name="test-model",
+            tokenizer=MagicMock(),
+            request_metadata=metadata,
+            created_time=0,
+            _increment_sequence_number_and_return=_identity_increment,
+        ):
+            events.append(event)
+        return events
+
+    @pytest.mark.skip_global_cleanup
+    @pytest.mark.asyncio
+    async def test_auto_multi_tool_streaming_opens_one_item_per_tool(self, monkeypatch):
+        monkeypatch.setattr(envs, "VLLM_USE_EXPERIMENTAL_PARSER_CONTEXT", False)
+
+        delta_sequence = [
+            DeltaMessage(
+                tool_calls=[
+                    DeltaToolCall(
+                        id="call_vienna",
+                        type="function",
+                        index=0,
+                        function=DeltaFunctionCall(
+                            name="get_weather",
+                            arguments="",
+                        ),
+                    )
+                ]
+            ),
+            DeltaMessage(
+                tool_calls=[
+                    DeltaToolCall(
+                        index=0,
+                        function=DeltaFunctionCall(
+                            arguments='{"location":"Vienna"}',
+                        ),
+                    )
+                ]
+            ),
+            DeltaMessage(
+                tool_calls=[
+                    DeltaToolCall(
+                        id="call_berlin",
+                        type="function",
+                        index=1,
+                        function=DeltaFunctionCall(
+                            name="get_weather",
+                            arguments='{"location":"Berlin"}',
+                        ),
+                    )
+                ]
+            ),
+        ]
+        events = await self._collect_events(delta_sequence)
+
+        function_items = [
+            event
+            for event in events
+            if event.type == "response.output_item.added"
+            and getattr(event.item, "type", None) == "function_call"
+        ]
+        assert len(function_items) == 2
+        assert [event.item.name for event in function_items] == [
+            "get_weather",
+            "get_weather",
+        ]
+        assert [event.output_index for event in function_items] == [0, 1]
+
+        argument_deltas = [
+            event.delta
+            for event in events
+            if event.type == "response.function_call_arguments.delta"
+        ]
+        assert argument_deltas == [
+            '{"location":"Vienna"}',
+            '{"location":"Berlin"}',
+        ]
+
+        argument_done = [
+            event
+            for event in events
+            if event.type == "response.function_call_arguments.done"
+        ]
+        assert [event.arguments for event in argument_done] == [
+            '{"location":"Vienna"}',
+            '{"location":"Berlin"}',
+        ]
+        assert [event.output_index for event in argument_done] == [0, 1]
+
+        function_done = [
+            event
+            for event in events
+            if event.type == "response.output_item.done"
+            and getattr(event.item, "type", None) == "function_call"
+        ]
+        assert [event.item.arguments for event in function_done] == [
+            '{"location":"Vienna"}',
+            '{"location":"Berlin"}',
+        ]
+        assert [event.output_index for event in function_done] == [0, 1]
+
+    @pytest.mark.skip_global_cleanup
+    @pytest.mark.asyncio
+    async def test_auto_tool_choice_first_delta_tool_call_does_not_duplicate_item(
+        self, monkeypatch
+    ):
+        monkeypatch.setattr(envs, "VLLM_USE_EXPERIMENTAL_PARSER_CONTEXT", False)
+
+        delta_sequence = [
+            DeltaMessage(
+                tool_calls=[
+                    DeltaToolCall(
+                        id="call_test",
+                        type="function",
+                        index=0,
+                        function=DeltaFunctionCall(
+                            name="get_weather",
+                            arguments="",
+                        ),
+                    )
+                ]
+            ),
+            DeltaMessage(
+                tool_calls=[
+                    DeltaToolCall(
+                        index=0,
+                        function=DeltaFunctionCall(
+                            arguments='{"location":"Berlin"}',
+                        ),
+                    )
+                ]
+            ),
+        ]
+        events = await self._collect_events(delta_sequence)
+
+        function_items = [
+            event
+            for event in events
+            if event.type == "response.output_item.added"
+            and getattr(event.item, "type", None) == "function_call"
+        ]
+        assert len(function_items) == 1
+        assert function_items[0].item.name == "get_weather"
+
+        argument_deltas = [
+            event.delta
+            for event in events
+            if event.type == "response.function_call_arguments.delta"
+        ]
+        assert "".join(argument_deltas) == '{"location":"Berlin"}'

vllm/entrypoints/openai/responses/serving.py

@@ -1341,6 +1341,7 @@ class OpenAIServingResponses(OpenAIServing):
         current_content_index = 0
         current_output_index = 0
         current_item_id = ""
+        current_tool_call_index: int | None = None
         parser = self.parser(tokenizer, request.tools) if self.parser else None
         first_delta_sent = False
         previous_delta_messages: list[DeltaMessage] = []
@@ -1368,6 +1369,7 @@ class OpenAIServingResponses(OpenAIServing):
                     )
                 if not delta_message:
                     continue
+                tool_call_item_started = False
                 if not first_delta_sent:
                     current_item_id = random_uuid()
                     if delta_message.tool_calls:
@@ -1384,6 +1386,7 @@ class OpenAIServingResponses(OpenAIServing):
                         current_tool_call_name = delta_message.tool_calls[
                             0
                         ].function.name
+                        current_tool_call_index = delta_message.tool_calls[0].index
                         yield _increment_sequence_number_and_return(
                             ResponseOutputItemAddedEvent(
                                 type="response.output_item.added",
@@ -1394,13 +1397,12 @@ class OpenAIServingResponses(OpenAIServing):
                                     id=current_item_id,
                                     call_id=current_tool_call_id,
                                     name=current_tool_call_name,
-                                    arguments=delta_message.tool_calls[
-                                        0
-                                    ].function.arguments,
+                                    arguments="",
                                     status="in_progress",
                                 ),
                             )
                         )
+                        tool_call_item_started = True
                     elif delta_message.reasoning:
                         yield _increment_sequence_number_and_return(
                             ResponseOutputItemAddedEvent(
@@ -1572,6 +1574,79 @@ class OpenAIServingResponses(OpenAIServing):
                     # reset previous delta messages
                     previous_delta_messages = []
                 if delta_message.tool_calls and delta_message.tool_calls[0].function:
+                    tool_call = delta_message.tool_calls[0]
+                    tool_call_function = tool_call.function
+                    if (
+                        current_tool_call_index is not None
+                        and tool_call.index is not None
+                        and tool_call.index != current_tool_call_index
+                        and tool_call_function is not None
+                        and tool_call_function.name is not None
+                    ):
+                        # From one tool call to another, finalize the previous
+                        # function-call item before opening the next one.
+                        parts = []
+                        for pm in previous_delta_messages:
+                            if pm.tool_calls:
+                                previous_tool_call = pm.tool_calls[0]
+                                if previous_tool_call.function is not None:
+                                    parts.append(
+                                        previous_tool_call.function.arguments or ""
+                                    )
+
+                        tool_call_arguments = "".join(parts)
+                        yield _increment_sequence_number_and_return(
+                            ResponseFunctionCallArgumentsDoneEvent(
+                                type="response.function_call_arguments.done",
+                                sequence_number=-1,
+                                output_index=current_output_index,
+                                item_id=current_item_id,
+                                arguments=tool_call_arguments,
+                                name=current_tool_call_name,
+                            )
+                        )
+                        function_call_item = ResponseFunctionToolCall(
+                            type="function_call",
+                            name=current_tool_call_name,
+                            arguments=tool_call_arguments,
+                            status="completed",
+                            id=current_item_id,
+                            call_id=current_tool_call_id,
+                        )
+                        yield _increment_sequence_number_and_return(
+                            ResponseOutputItemDoneEvent(
+                                type="response.output_item.done",
+                                sequence_number=-1,
+                                output_index=current_output_index,
+                                item=function_call_item,
+                            )
+                        )
+                        # Reset previous delta messages so the next tool call
+                        # does not reuse arguments from the completed item.
+                        previous_delta_messages = []
+                        current_output_index += 1
+                        current_item_id = random_uuid()
+                        current_tool_call_name = tool_call_function.name
+                        current_tool_call_id = f"call_{random_uuid()}"
+                        current_tool_call_index = tool_call.index
+                        yield _increment_sequence_number_and_return(
+                            ResponseOutputItemAddedEvent(
+                                type="response.output_item.added",
+                                sequence_number=-1,
+                                output_index=current_output_index,
+                                item=ResponseFunctionToolCallItem(
+                                    type="function_call",
+                                    id=current_item_id,
+                                    call_id=current_tool_call_id,
+                                    name=current_tool_call_name,
+                                    arguments="",
+                                    status="in_progress",
+                                ),
+                            )
+                        )
+                        current_content_index = 0
+                        tool_call_item_started = True
+
                     if delta_message.tool_calls[0].function.arguments:
                         yield _increment_sequence_number_and_return(
                             ResponseFunctionCallArgumentsDeltaEvent(
@@ -1583,7 +1658,10 @@ class OpenAIServingResponses(OpenAIServing):
                             )
                         )
                     # tool call initiated with no arguments
-                    elif delta_message.tool_calls[0].function.name:
+                    elif (
+                        delta_message.tool_calls[0].function.name
+                        and not tool_call_item_started
+                    ):
                         # send done with current content part
                         # and add new function call item
                         yield _increment_sequence_number_and_return(
@@ -1628,11 +1706,11 @@ class OpenAIServingResponses(OpenAIServing):
                         )
                         current_output_index += 1
                         current_item_id = random_uuid()
-                        assert delta_message.tool_calls[0].function is not None
                         current_tool_call_name = delta_message.tool_calls[
                             0
                         ].function.name
                         current_tool_call_id = f"call_{random_uuid()}"
+                        current_tool_call_index = delta_message.tool_calls[0].index
                         yield _increment_sequence_number_and_return(
                             ResponseOutputItemAddedEvent(
                                 type="response.output_item.added",