[gpt-oss] Support chat completion api (#22342)

vllm/entrypoints/harmony_utils.py

@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: Apache-2.0
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 import datetime
+from collections.abc import Iterable
 from typing import Literal, Optional
 
 from openai.types.responses.tool import Tool
@@ -109,3 +110,36 @@ def get_stop_tokens_for_assistant_actions() -> list[int]:
 
 def get_streamable_parser_for_assistant() -> StreamableParser:
     return StreamableParser(get_encoding(), role=Role.ASSISTANT)
+
+
+def parse_output_into_messages(token_ids: Iterable[int]) -> StreamableParser:
+    parser = get_streamable_parser_for_assistant()
+    for token_id in token_ids:
+        parser.process(token_id)
+    return parser
+
+
+def parse_chat_output(
+        token_ids: list[int]) -> tuple[Optional[str], Optional[str], bool]:
+    parser = parse_output_into_messages(token_ids)
+    output_msgs = parser.messages
+    if len(output_msgs) == 0:
+        # The generation has stopped during reasoning.
+        is_tool_call = False
+        reasoning_content = parser.current_content
+        final_content = None
+    elif len(output_msgs) == 1:
+        # The generation has stopped during final message.
+        is_tool_call = False
+        reasoning_content = output_msgs[0].content[0].text
+        final_content = parser.current_content
+    else:
+        if len(output_msgs) != 2:
+            raise ValueError(
+                "Expected 2 output messages (reasoning and final), "
+                f"but got {len(output_msgs)}.")
+        reasoning_msg, final_msg = output_msgs
+        reasoning_content = reasoning_msg.content[0].text
+        final_content = final_msg.content[0].text
+        is_tool_call = final_msg.recipient is not None
+    return reasoning_content, final_content, is_tool_call