Fix cors (#942)

(cherry picked from commit a012c68)

Author: vishalbollu

pkg/workloads/cortex/serve/serve.py

@@ -25,6 +25,7 @@
 
 from fastapi import Body, FastAPI
 from fastapi.exceptions import RequestValidationError
+from fastapi.middleware.cors import CORSMiddleware
 from starlette.requests import Request
 from starlette.responses import Response
 from starlette.background import BackgroundTasks
@@ -55,6 +56,15 @@
 )
 
 app = FastAPI()
+
+app.add_middleware(
+    CORSMiddleware,
+    allow_origins=["*"],
+    allow_credentials=True,
+    allow_methods=["*"],
+    allow_headers=["*"],
+)
+
 local_cache = {"api": None, "predictor_impl": None, "client": None, "class_set": set()}
 
 
@@ -90,21 +100,18 @@ def is_prediction_request(request):
 @app.exception_handler(StarletteHTTPException)
 async def http_exception_handler(request, e):
     response = Response(content=str(e.detail), status_code=e.status_code)
-    apply_cors_headers(request, response)
     return response
 
 
 @app.exception_handler(RequestValidationError)
 async def validation_exception_handler(request, e):
     response = Response(content=str(e), status_code=400)
-    apply_cors_headers(request, response)
     return response
 
 
 @app.exception_handler(Exception)
 async def uncaught_exception_handler(request, e):
     response = Response(content="internal server error", status_code=500)
-    apply_cors_headers(request, response)
     return response
 
 
@@ -132,20 +139,12 @@ async def register_request(request: Request, call_next):
             status_code = 500
             if response is not None:
                 status_code = response.status_code
-                apply_cors_headers(request, response)
             api = local_cache["api"]
             api.post_request_metrics(status_code, time.time() - request.state.start_time)
 
     return response
 
 
-def apply_cors_headers(request: Request, response: Response):
-    response.headers["Access-Control-Allow-Origin"] = "*"
-    response.headers["Access-Control-Allow-Headers"] = request.headers.get(
-        "Access-Control-Request-Headers", "*"
-    )
-
-
 @app.post("/predict")
 def predict(request: Any = Body(..., media_type="application/json"), debug=False):
     api = local_cache["api"]