Run the server and make following reqeust to test forward function. Remember to set forward=ok in the header so the middleware can tell which one is for forward and which one is for reverse. The demo can be adapted to puer forward proxy.

import requests
def test_forward():
  res=requests.get("http://www.baidu.com",headers={"forward":"ok"},proxies={"http":"http://127.0.0.1:8888"})
  print (res.text)
test_forward()