[Server] Add option to specify chat template for chat endpoint (#345)

requirements.txt

@@ -9,3 +9,4 @@ xformers >= 0.0.19
 fastapi
 uvicorn
 pydantic  # Required for OpenAI server.
+fschat  # Required for OpenAI ChatCompletion Endpoint.

vllm/entrypoints/openai/api_server.py

@@ -36,6 +36,7 @@ TIMEOUT_KEEP_ALIVE = 5  # seconds
 
 logger = init_logger(__name__)
 served_model = None
+chat_template = None
 app = fastapi.FastAPI()
 
 
@@ -62,7 +63,7 @@ async def check_model(request) -> Optional[JSONResponse]:
 
 
 async def get_gen_prompt(request) -> str:
-    conv = get_conv_template(request.model)
+    conv = get_conv_template(chat_template)
     conv = Conversation(
         name=conv.name,
         system=conv.system,
@@ -553,13 +554,20 @@ if __name__ == "__main__":
                         type=json.loads,
                         default=["*"],
                         help="allowed headers")
+    parser.add_argument("--served-model-name",
+                        type=str,
+                        default=None,
+                        help="The model name used in the API. If not "
+                        "specified, the model name will be the same as "
+                        "the huggingface name.")
     parser.add_argument(
-        "--served-model-name",
+        "--chat-template",
         type=str,
         default=None,
-        help="The model name used in the API. If not specified, "
-        "the model name will be the same as the "
-        "huggingface name.")
+        help="The chat template name used in the ChatCompletion endpoint. If "
+        "not specified, we use the API model name as the template name. See "
+        "https://github.com/lm-sys/FastChat/blob/main/fastchat/conversation.py "
+        "for the list of available templates.")
     parser = AsyncEngineArgs.add_cli_args(parser)
     args = parser.parse_args()
 
@@ -573,7 +581,15 @@ if __name__ == "__main__":
 
     logger.info(f"args: {args}")
 
-    served_model = args.served_model_name or args.model
+    if args.served_model_name is not None:
+        served_model = args.served_model_name
+    else:
+        served_model = args.model
+
+    if args.chat_template is not None:
+        chat_template = args.chat_template
+    else:
+        chat_template = served_model
 
     engine_args = AsyncEngineArgs.from_cli_args(args)
     engine = AsyncLLMEngine.from_engine_args(engine_args)