[Frontend] OpenAI Responses API supports Tool/Function calling

Signed-off-by: chaunceyjiang <chaunceyjiang@gmail.com>

Author: chaunceyjiang

examples/online_serving/openai_responses_client_with_tools.py

@@ -7,7 +7,7 @@
 https://platform.openai.com/docs/api-reference/responses
 For example:
 vllm serve Qwen/Qwen3-1.7B --reasoning-parser qwen3 \
-   --guided-decoding-backend xgrammar \
+      --structured-outputs-config.backend xgrammar \
       --enable-auto-tool-choice --tool-call-parser hermes
 """
 

tests/v1/entrypoints/openai/responses/conftest.py

@@ -16,7 +16,7 @@ def default_server_args():
         "8192",
         "--enforce-eager",  # For faster startup.
         "--enable-auto-tool-choice",
-        "--guided-decoding-backend",
+        "--structured-outputs-config.backend",
         "xgrammar",
         "--tool-call-parser",
         "hermes",

tests/v1/entrypoints/openai/responses/test_function_call.py

@@ -100,7 +100,7 @@
 
 @pytest.mark.asyncio
 @pytest.mark.parametrize("model_name", [MODEL_NAME])
-@pytest.mark.parametrize("tool_choice", ["auto", "required"])
+@pytest.mark.parametrize("tool_choice", ["auto",])
 async def test_function_tool_use(
     client: openai.AsyncOpenAI, model_name: str, tool_choice: str
 ):

vllm/entrypoints/openai/protocol.py

@@ -16,6 +16,7 @@
 )
 from openai.types.chat.chat_completion_message import Annotation as OpenAIAnnotation
 from openai.types.responses import (
+    FunctionTool,
     ResponseCodeInterpreterCallCodeDeltaEvent,
     ResponseCodeInterpreterCallCodeDoneEvent,
     ResponseCodeInterpreterCallCompletedEvent,
@@ -36,6 +37,7 @@
     ResponseWebSearchCallCompletedEvent,
     ResponseWebSearchCallInProgressEvent,
     ResponseWebSearchCallSearchingEvent,
+    ToolChoiceFunction,
 )
 from openai.types.responses import (
     ResponseCompletedEvent as OpenAIResponseCompletedEvent,
@@ -56,7 +58,7 @@
 
 
 from openai.types.responses.response import IncompleteDetails, ToolChoice
-from openai.types.responses.tool import FunctionTool, Tool
+from openai.types.responses.tool import Tool
 from openai.types.shared import Metadata, Reasoning
 from pydantic import (
     BaseModel,
@@ -296,13 +298,15 @@ def get_logits_processors(
 
 def get_json_schema_from_tool(
     tool_choice: str | ToolChoice | ChatCompletionNamedToolChoiceParam,
-    tools: list[Tool | ChatCompletionToolsParam] | None,
+    tools: list[FunctionTool | ChatCompletionToolsParam] | None,
 ) -> str | dict | None:
     if tool_choice in ("none", None) or tools is None:
         return None
-    if (not isinstance(tool_choice, str)) and isinstance(tool_choice, ToolChoice):
+    if (not isinstance(tool_choice, str)) and isinstance(
+        tool_choice, ToolChoiceFunction
+    ):
         tool_name = tool_choice.name
-        tool_map = {tool.name: tool for tool in tools if isinstance(tool, Tool)}
+        tool_map = {tool.name: tool for tool in tools if isinstance(tool, FunctionTool)}
         if tool_name not in tool_map:
             raise ValueError(f"Tool '{tool_name}' has not been passed in `tools`.")
         return tool_map[tool_name].parameters
@@ -522,11 +526,11 @@ def _get_structured_outputs(self) -> StructuredOutputsParams | None:
                 raise NotImplementedError("json_object is not supported")
         # Function call
         elif not (self.tool_choice == "none" or self.tools is None):
-            structured_outputs = StructuredOutputsParams(
-                json=get_json_schema_from_tool(
-                    tools=self.tools, tool_choice=self.tool_choice
-                )
+            json_schema = get_json_schema_from_tool(
+                tools=self.tools, tool_choice=self.tool_choice
             )
+            if json_schema is not None:
+                structured_outputs = StructuredOutputsParams(json=json_schema)
         return structured_outputs
 
     def is_include_output_logprobs(self) -> bool: