code: def test_uvicorn_duplicate_headers(serve_instance):
      # https://github.com/ray-project/ray/issues/21876
      app = FastAPI()
  
      @serve.deployment
      @serve.ingress(app)
      class A:
          @app.get("/")
          def func(self):
              return JSONResponse({"a": "b"})
  
      serve.run(A.bind())
      resp = requests.get("http://127.0.0.1:8000")
      # If the header duplicated, it will be "9, 9"
      assert resp.headers["content-length"] == "9"
  
imports: import asyncio
  import gc
  import sys
  import numpy
  import pytest
  import requests
  from fastapi import FastAPI
  from fastapi.responses import JSONResponse
  import ray
  from ray import serve
  from ray._private.test_utils import SignalActor
  from ray.serve.context import _get_global_client
  from ray.serve.handle import DeploymentHandle
label_desc: Use image node_id 9 for calling a global function with example usage: test_uvicorn_duplicate_headers(serve_instance) and returns: JSONResponse