[GPT-OSS] Add support for arrays at tool message content (#25593)

Signed-off-by: Luis Tomas Bolivar <ltomasbo@redhat.com>

tests/entrypoints/openai/test_serving_chat.py

@@ -207,6 +207,138 @@ async def test_gpt_oss_multi_turn_chat(gptoss_client: OpenAI, with_tool_parser:
     )
 
 
+@pytest.mark.asyncio
+async def test_gpt_oss_tool_message_array_content(gptoss_client: OpenAI,
+                                                  with_tool_parser: bool):
+    """Test that tool messages support both string and array content formats."""
+    if not with_tool_parser:
+        pytest.skip("skip non-tool for array content tests")
+
+    tools = [{
+        "type": "function",
+        "function": {
+            "name": "get_weather",
+            "description": "Get the current weather in a given location",
+            "parameters": {
+                "type": "object",
+                "properties": {
+                    "city": {
+                        "type": "string"
+                    },
+                    "state": {
+                        "type": "string"
+                    },
+                },
+                "required": ["city", "state"],
+            },
+        },
+    }]
+
+    # Test 1: Tool message with string content
+    messages_string = [{
+        "role": "user",
+        "content": "What's the weather in Paris?"
+    }, {
+        "role":
+        "assistant",
+        "tool_calls": [{
+            "id": "call_123",
+            "type": "function",
+            "function": {
+                "name": "get_weather",
+                "arguments": '{"city": "Paris", "state": "TX"}'
+            }
+        }]
+    }, {
+        "role": "tool",
+        "content": "The weather in Paris, TX is sunny, 22°C"
+    }]
+
+    response_string = await gptoss_client.chat.completions.create(
+        model=GPT_OSS_MODEL_NAME,
+        messages=messages_string,
+        tools=tools,
+        temperature=0.0,
+    )
+
+    assert response_string is not None
+    assert response_string.choices[0].message is not None
+
+    # Test 2: Tool message with array content
+    messages_array = [{
+        "role": "user",
+        "content": "What's the weather in Dallas?"
+    }, {
+        "role":
+        "assistant",
+        "tool_calls": [{
+            "id": "call_456",
+            "type": "function",
+            "function": {
+                "name": "get_weather",
+                "arguments": '{"city": "Dallas", "state": "TX"}'
+            }
+        }]
+    }, {
+        "role":
+        "tool",
+        "content": [{
+            "type": "text",
+            "text": "f2e897a7-2705-4337-8193-2a8f57b81618"
+        }]
+    }]
+
+    response_array = await gptoss_client.chat.completions.create(
+        model=GPT_OSS_MODEL_NAME,
+        messages=messages_array,
+        tools=tools,
+        temperature=0.0,
+    )
+
+    assert response_array is not None
+    assert response_array.choices[0].message is not None
+
+    # Test 3: Tool message with multiple array content items
+    messages_multi_array = [{
+        "role": "user",
+        "content": "Search for information"
+    }, {
+        "role":
+        "assistant",
+        "tool_calls": [{
+            "id": "call_789",
+            "type": "function",
+            "function": {
+                "name": "get_weather",
+                "arguments": '{"city": "Austin", "state": "TX"}'
+            }
+        }]
+    }, {
+        "role":
+        "tool",
+        "content": [{
+            "type": "text",
+            "text": "Weather data: "
+        }, {
+            "type": "text",
+            "text": "Austin, TX - Partly cloudy, 25°C"
+        }, {
+            "type": "text",
+            "text": " with 60% humidity"
+        }]
+    }]
+
+    response_multi_array = await gptoss_client.chat.completions.create(
+        model=GPT_OSS_MODEL_NAME,
+        messages=messages_multi_array,
+        tools=tools,
+        temperature=0.0,
+    )
+
+    assert response_multi_array is not None
+    assert response_multi_array.choices[0].message is not None
+
+
 MODEL_NAME = "openai-community/gpt2"
 MODEL_NAME_SHORT = "gpt2"
 CHAT_TEMPLATE = "Dummy chat template for testing {}"

vllm/entrypoints/harmony_utils.py

@@ -256,6 +256,13 @@ def parse_chat_input(chat_msg) -> list[Message]:
     if role == "tool":
         name = chat_msg.get("name", "")
         content = chat_msg.get("content", "") or ""
+        if isinstance(content, list):
+            # Handle array format for tool message content
+            # by concatenating all text parts.
+            content = "".join(
+                item.get("text", "") for item in content
+                if isinstance(item, dict) and item.get("type") == "text")
+
         msg = Message.from_author_and_content(
             Author.new(Role.TOOL, f"functions.{name}"), content
         ).with_channel("commentary")