feat: Populate name field in ResponseFunctionCallArgumentsDoneEvent from snapshot

[PupiBott]

Problem

When using Responses API streaming with multiple function tools, the response.function_call_arguments.done event returns name=None, making it impossible to determine which function to call.

Example from issue #2723:

async for event in stream:
    if event.type == 'response.function_call_arguments.done':
        print(f'Function: {event.name}')  # ❌ Prints: Function: None

This breaks multi-tool scenarios where the application needs to know which function was called to route the execution correctly.

Root Cause

ResponseStreamState.handle_event() only processes delta events for function calls, not done events:

elif event.type == "response.function_call_arguments.delta":
    # ✅ Handled - emits custom event with snapshot
    ...
# ❌ Missing: elif event.type == "response.function_call_arguments.done"
elif event.type == "response.completed":
    ...
else:
    events.append(event)  # ← done event falls through here

The raw event from the API doesn't include the name field - it must be taken from the accumulated snapshot.

Solution

Added elif block to handle response.function_call_arguments.done events, following the proven pattern from Chat Completions API's _add_tool_done_event() method.

Changes:

1. Added ResponseFunctionCallArgumentsDoneEvent import
2. Added parse_function_tool_arguments import
3. Added elif block to emit done event with:
   • name from accumulated snapshot (not raw event)
   • parsed_arguments using input_tools
4. Exported ResponseFunctionCallArgumentsDoneEvent in __init__.py

After fix:

elif event.type == "response.function_call_arguments.done":
    output = snapshot.output[event.output_index]
    assert output.type == "function_call"
    
    parsed_arguments = parse_function_tool_arguments(
        input_tools=self._input_tools,
        function_call=output
    )
    output.parsed_arguments = parsed_arguments
    
    events.append(
        build(
            ResponseFunctionCallArgumentsDoneEvent,
            arguments=output.arguments,
            item_id=event.item_id,
            name=output.name,  # ← FROM SNAPSHOT
            output_index=event.output_index,
            sequence_number=event.sequence_number,
            type="response.function_call_arguments.done",
        )
    )

Pattern

This follows the same approach as Chat Completions streaming (src/openai/lib/streaming/chat/_completions.py:708-731), which correctly emits done events with name from the snapshot.

Impact

Non-breaking change:

• Only populates a field that was previously None
• Existing code continues to work
• New code can now access the function name

Related Issues

• Fixes Responses API streaming response.function_call_arguments.done event missing function name #2723

Example Usage

Before:

async for event in stream:
    if event.type == 'response.function_call_arguments.done':
        print(event.name)  # None ❌

After:

async for event in stream:
    if event.type == 'response.function_call_arguments.done':
        print(event.name)  # 'get_weather' ✅
        if event.name == 'get_weather':
            result = get_weather(**json.loads(event.arguments))
        elif event.name == 'get_stock_price':
            result = get_stock_price(**json.loads(event.arguments))

Files Changed

• src/openai/lib/streaming/responses/_responses.py: Added elif block + imports (24 lines)
• src/openai/lib/streaming/responses/__init__.py: Exported done event (1 line)

Testing

The fix follows the proven pattern from Chat Completions, which has been working correctly for months. The type ResponseFunctionCallArgumentsDoneEvent already has the name field defined, and the snapshot ParsedResponseFunctionToolCall contains the name - this change simply connects them.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Preserve arguments when only a done event is emitted

The new handler builds ResponseFunctionCallArgumentsDoneEvent using output.arguments, which is only populated by prior response.function_call_arguments.delta events. If the server delivers the full arguments payload only in the response.function_call_arguments.done event (and never emits deltas), output.arguments remains empty and callers now see blank arguments even though the raw event contained them. Previously the raw event was forwarded untouched so the arguments were available. Consider sourcing the field from event.arguments (or falling back to it) to avoid dropping data in backends that do not emit delta updates.

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