[Frontend] Re-enable custom roles in Chat Completions API (#4758)

tests/entrypoints/test_openai_server.py

@@ -783,6 +783,36 @@ async def test_complex_message_content(server, client: openai.AsyncOpenAI):
     assert content == "2"
 
 
+async def test_custom_role(server, client: openai.AsyncOpenAI):
+    # Not sure how the model handles custom roles so we just check that
+    # both string and complex message content are handled in the same way
+
+    resp1 = await client.chat.completions.create(
+        model=MODEL_NAME,
+        messages=[{
+            "role": "my-custom-role",
+            "content": "what is 1+1?",
+        }],  # type: ignore
+        temperature=0,
+        seed=0)
+
+    resp2 = await client.chat.completions.create(
+        model=MODEL_NAME,
+        messages=[{
+            "role": "my-custom-role",
+            "content": [{
+                "type": "text",
+                "text": "what is 1+1?"
+            }]
+        }],  # type: ignore
+        temperature=0,
+        seed=0)
+
+    content1 = resp1.choices[0].message.content
+    content2 = resp2.choices[0].message.content
+    assert content1 == content2
+
+
 async def test_guided_grammar(server, client: openai.AsyncOpenAI):
     simple_sql_grammar = """
 start: select_statement

vllm/entrypoints/openai/protocol.py

@@ -3,16 +3,50 @@
 import time
 from typing import Any, Dict, List, Literal, Optional, Union
 
+import openai.types.chat
 import torch
-from openai.types.chat import ChatCompletionMessageParam
 from pydantic import BaseModel, ConfigDict, Field, model_validator
-from typing_extensions import Annotated
+# pydantic needs the TypedDict from typing_extensions
+from typing_extensions import Annotated, Required, TypedDict
 
 from vllm.pooling_params import PoolingParams
 from vllm.sampling_params import SamplingParams
 from vllm.utils import random_uuid
 
 
+class CustomChatCompletionContentPartParam(TypedDict, total=False):
+    __pydantic_config__ = ConfigDict(extra="allow")  # type: ignore
+
+    type: Required[str]
+    """The type of the content part."""
+
+
+ChatCompletionContentPartParam = Union[
+    openai.types.chat.ChatCompletionContentPartParam,
+    CustomChatCompletionContentPartParam]
+
+
+class CustomChatCompletionMessageParam(TypedDict, total=False):
+    """Enables custom roles in the Chat Completion API."""
+    role: Required[str]
+    """The role of the message's author."""
+
+    content: Union[str, List[ChatCompletionContentPartParam]]
+    """The contents of the message."""
+
+    name: str
+    """An optional name for the participant.
+
+    Provides the model information to differentiate between participants of the
+    same role.
+    """
+
+
+ChatCompletionMessageParam = Union[
+    openai.types.chat.ChatCompletionMessageParam,
+    CustomChatCompletionMessageParam]
+
+
 class OpenAIBaseModel(BaseModel):
     # OpenAI API does not allow extra fields
     model_config = ConfigDict(extra="forbid")

vllm/entrypoints/openai/serving_chat.py

 import codecs
 import time
-from typing import (AsyncGenerator, AsyncIterator, Awaitable, Iterable, List,
-                    Optional, Tuple, TypedDict, Union, final)
+from dataclasses import dataclass
+from typing import (AsyncGenerator, AsyncIterator, Iterable, List, Optional,
+                    TypedDict, Union, cast, final)
 
 from fastapi import Request
-from openai.types.chat import (ChatCompletionContentPartParam,
-                               ChatCompletionRole)
+from openai.types.chat import ChatCompletionContentPartTextParam
 
 from vllm.config import ModelConfig
 from vllm.engine.async_llm_engine import AsyncLLMEngine
 from vllm.entrypoints.openai.protocol import (
+    ChatCompletionContentPartParam, ChatCompletionMessageParam,
     ChatCompletionRequest, ChatCompletionResponse,
     ChatCompletionResponseChoice, ChatCompletionResponseStreamChoice,
     ChatCompletionStreamResponse, ChatMessage, DeltaMessage, ErrorResponse,
@@ -31,6 +32,11 @@ class ConversationMessage(TypedDict):
     content: str
 
 
+@dataclass(frozen=True)
+class ChatMessageParseResult:
+    messages: List[ConversationMessage]
+
+
 class OpenAIServingChat(OpenAIServing):
 
     def __init__(self,
@@ -77,27 +83,40 @@ class OpenAIServingChat(OpenAIServing):
             logger.warning(
                 "No chat template provided. Chat API will not work.")
 
-    def _parse_chat_message_content(
+    def _parse_chat_message_content_parts(
         self,
-        role: ChatCompletionRole,
-        content: Optional[Union[str,
-                                Iterable[ChatCompletionContentPartParam]]],
-    ) -> Tuple[List[ConversationMessage], List[Awaitable[object]]]:
-        if content is None:
-            return [], []
-        if isinstance(content, str):
-            return [ConversationMessage(role=role, content=content)], []
-
+        role: str,
+        parts: Iterable[ChatCompletionContentPartParam],
+    ) -> ChatMessageParseResult:
         texts: List[str] = []
-        for _, part in enumerate(content):
-            if part["type"] == "text":
-                text = part["text"]
+
+        for _, part in enumerate(parts):
+            part_type = part["type"]
+            if part_type == "text":
+                text = cast(ChatCompletionContentPartTextParam, part)["text"]
 
                 texts.append(text)
             else:
-                raise NotImplementedError(f"Unknown part type: {part['type']}")
+                raise NotImplementedError(f"Unknown part type: {part_type}")
+
+        messages = [ConversationMessage(role=role, content="\n".join(texts))]
+
+        return ChatMessageParseResult(messages=messages)
+
+    def _parse_chat_message_content(
+        self,
+        message: ChatCompletionMessageParam,
+    ) -> ChatMessageParseResult:
+        role = message["role"]
+        content = message.get("content")
+
+        if content is None:
+            return ChatMessageParseResult(messages=[])
+        if isinstance(content, str):
+            messages = [ConversationMessage(role=role, content=content)]
+            return ChatMessageParseResult(messages=messages)
 
-        return [ConversationMessage(role=role, content="\n".join(texts))], []
+        return self._parse_chat_message_content_parts(role, content)
 
     async def create_chat_completion(
         self, request: ChatCompletionRequest, raw_request: Request
@@ -119,11 +138,10 @@ class OpenAIServingChat(OpenAIServing):
         try:
             conversation: List[ConversationMessage] = []
 
-            for m in request.messages:
-                messages, _ = self._parse_chat_message_content(
-                    m["role"], m["content"])
+            for msg in request.messages:
+                parsed_msg = self._parse_chat_message_content(msg)
 
-                conversation.extend(messages)
+                conversation.extend(parsed_msg.messages)
 
             prompt = self.tokenizer.apply_chat_template(
                 conversation=conversation,