Simple RSS proxy to add title elements to a Mastodon feed

app.py

# put in rss_proxy/ as app.py and run with `python -m flask run`
# requirements: flask beautifulsoup4 requests lxml
# usage: `curl localhost:5000?feed=https://instance.example.com/users/username.rss`

from bs4 import BeautifulSoup
from flask import Flask, request
import requests
from lxml.builder import E
import lxml.etree

app = Flask(__name__)

@app.route("/", methods=["GET"])
def index():
  feed = requests.get(request.args["feed"])
  feed.raise_for_status()
  feed_xml = lxml.etree.fromstring(feed.text.encode("utf-8"), parser=None)

  for tag in feed_xml.find("channel").findall("item"):
    desc = BeautifulSoup(tag.find("description").text).text # strip html tags
    truncated = desc[:100] # or desired length
    tag.append(E.title(truncated))

  return lxml.etree.tostring(feed_xml)