[Frontend] Support complex message content for chat completions endpoint (#3467)

Co-authored-by: Lily Liu <lilyliupku@gmail.com>
Co-authored-by: Cyrus Leung <tlleungac@connect.ust.hk>

tests/entrypoints/test_openai_server.py

@@ -786,6 +786,25 @@ async def test_extra_fields(server, client: openai.AsyncOpenAI):
     assert "extra_forbidden" in exc_info.value.message
 
 
+async def test_complex_message_content(server, client: openai.AsyncOpenAI):
+    resp = await client.chat.completions.create(
+        model=MODEL_NAME,
+        messages=[{
+            "role":
+            "user",
+            "content": [{
+                "type":
+                "text",
+                "text":
+                "what is 1+1? please provide the result without any other text."
+            }]
+        }],
+        temperature=0,
+        seed=0)
+    content = resp.choices[0].message.content
+    assert content == "2"
+
+
 async def test_guided_grammar(server, client: openai.AsyncOpenAI):
     simple_sql_grammar = """
 start: select_statement

vllm/entrypoints/openai/serving_chat.py

@@ -55,9 +55,16 @@ class OpenAIServingChat(OpenAIServing):
         if isinstance(content, str):
             return [ConversationMessage(role=role, content=content)], []
 
-        # To be implemented: https://github.com/vllm-project/vllm/pull/3467
-        # To be implemented: https://github.com/vllm-project/vllm/pull/4200
-        raise NotImplementedError("Complex input not supported yet")
+        texts: List[str] = []
+        for _, part in enumerate(content):
+            if part["type"] == "text":
+                text = part["text"]
+
+                texts.append(text)
+            else:
+                raise NotImplementedError(f"Unknown part type: {part['type']}")
+
+        return [ConversationMessage(role=role, content="\n".join(texts))], []
 
     async def create_chat_completion(
         self, request: ChatCompletionRequest, raw_request: Request
@@ -122,11 +129,12 @@ class OpenAIServingChat(OpenAIServing):
         # Streaming response
         if request.stream:
             return self.chat_completion_stream_generator(
-                request, result_generator, request_id)
+                request, result_generator, request_id, conversation)
         else:
             try:
                 return await self.chat_completion_full_generator(
-                    request, raw_request, result_generator, request_id)
+                    request, raw_request, result_generator, request_id,
+                    conversation)
             except ValueError as e:
                 # TODO: Use a vllm-specific Validation Error
                 return self.create_error_response(str(e))
@@ -139,8 +147,9 @@ class OpenAIServingChat(OpenAIServing):
 
     async def chat_completion_stream_generator(
             self, request: ChatCompletionRequest,
-            result_generator: AsyncIterator[RequestOutput],
-            request_id: str) -> AsyncGenerator[str, None]:
+            result_generator: AsyncIterator[RequestOutput], request_id: str,
+            conversation: List[ConversationMessage]
+    ) -> AsyncGenerator[str, None]:
         model_name = self.served_model_names[0]
         created_time = int(time.time())
         chunk_object_type = "chat.completion.chunk"
@@ -179,12 +188,10 @@ class OpenAIServingChat(OpenAIServing):
                     # last message
                     if request.echo:
                         last_msg_content = ""
-                        if request.messages and isinstance(
-                                request.messages,
-                                list) and request.messages[-1].get(
-                                    "content") and request.messages[-1].get(
+                        if conversation and conversation[-1].get(
+                                "content") and conversation[-1].get(
                                     "role") == role:
-                            last_msg_content = request.messages[-1]["content"]
+                            last_msg_content = conversation[-1]["content"]
 
                         if last_msg_content:
                             for i in range(request.n):
@@ -280,8 +287,9 @@ class OpenAIServingChat(OpenAIServing):
 
     async def chat_completion_full_generator(
         self, request: ChatCompletionRequest, raw_request: Request,
-            result_generator: AsyncIterator[RequestOutput],
-            request_id: str) -> Union[ErrorResponse, ChatCompletionResponse]:
+        result_generator: AsyncIterator[RequestOutput], request_id: str,
+        conversation: List[ConversationMessage]
+    ) -> Union[ErrorResponse, ChatCompletionResponse]:
 
         model_name = self.served_model_names[0]
         created_time = int(time.time())
@@ -322,11 +330,9 @@ class OpenAIServingChat(OpenAIServing):
 
         if request.echo:
             last_msg_content = ""
-            if request.messages and isinstance(
-                    request.messages, list) and request.messages[-1].get(
-                        "content") and request.messages[-1].get(
-                            "role") == role:
-                last_msg_content = request.messages[-1]["content"]
+            if conversation and conversation[-1].get(
+                    "content") and conversation[-1].get("role") == role:
+                last_msg_content = conversation[-1]["content"]
 
             for choice in choices:
                 full_message = last_msg_content + choice.message.content