Support CORS for openai api server (#481)

* Support CORS for openai api server

* Remove unnecessary var

* Add CORS support follow the same style with vllm

lmdeploy/serve/openai/api_server.py

@@ -3,11 +3,12 @@
 import os
 import time
 from http import HTTPStatus
-from typing import AsyncGenerator, Optional
+from typing import AsyncGenerator, List, Optional
 
 import fire
 import uvicorn
 from fastapi import BackgroundTasks, FastAPI, Request
+from fastapi.middleware.cors import CORSMiddleware
 from fastapi.responses import JSONResponse, StreamingResponse
 
 from lmdeploy.serve.async_engine import AsyncEngine
@@ -321,7 +322,11 @@ def main(model_path: str,
          server_name: str = 'localhost',
          server_port: int = 23333,
          instance_num: int = 32,
-         tp: int = 1):
+         tp: int = 1,
+         allow_origins: List[str] = ['*'],
+         allow_credentials: bool = True,
+         allow_methods: List[str] = ['*'],
+         allow_headers: List[str] = ['*']):
     """An example to perform model inference through the command line
     interface.
 
@@ -331,7 +336,20 @@ def main(model_path: str,
         server_port (int): server port
         instance_num (int): number of instances of turbomind model
         tp (int): tensor parallel
+        allow_origins (List[str]): a list of allowed origins for CORS
+        allow_credentials (bool): whether to allow credentials for CORS
+        allow_methods (List[str]): a list of allowed HTTP methods for CORS
+        allow_headers (List[str]): a list of allowed HTTP headers for CORS
     """
+    if allow_origins:
+        app.add_middleware(
+            CORSMiddleware,
+            allow_origins=allow_origins,
+            allow_credentials=allow_credentials,
+            allow_methods=allow_methods,
+            allow_headers=allow_headers,
+        )
+
     VariableInterface.async_engine = AsyncEngine(model_path=model_path,
                                                  instance_num=instance_num,
                                                  tp=tp)