Flask view decorator for injecting Cache-Control headers

README.md

POC decorator for flask fiew functions to inject Cache-Control headers in a response.

Instructions to run example

Set up env, for example:

python -m venv venv
. venv/bin/activate
pip install flask

Run flask app:

export FLASK_APP=example.py
export FLASK_ENV=development 
flask run

Visit http://127.0.0.1:5000/, e.g.

$ curl -i http://127.0.0.1:5000/

HTTP/1.1 200 OK
...
Cache-Control: max-age=900, public
Expires: Wed, 01 Jun 2022 16:00:36 GMT
...
{
  "hello": "world"
}

cache_control.py

import datetime
import functools

import flask


def cache_control(
        max_age=None, no_cache=None, no_store=None,
        public=None, private=None, must_revalidate=None,
):
    """
    Parameterized decorator for Flask view functions to set `Cache-Control` headers on the response.
    """
    if isinstance(max_age, datetime.timedelta):
        max_age = int(max_age.total_seconds())

    settings = dict(
        max_age=max_age, no_cache=no_cache, no_store=no_store,
        public=public, private=private, must_revalidate=must_revalidate,
    )
    settings = {key: value for key, value in settings.items() if value is not None}

    def add_cache_control_headers(response: flask.Response) -> flask.Response:
        # TODO: option to take status code into account
        if 200 <= response.status_code < 300:
            for key, value in settings.items():
                setattr(response.cache_control, key, value)
            if max_age is not None:
                response.expires = datetime.datetime.utcnow() + datetime.timedelta(seconds=max_age)
        return response

    def decorator(func):
        @functools.wraps(func)
        def wrapped(*args, **kwargs):
            flask.after_this_request(add_cache_control_headers)
            return func(*args, **kwargs)

        return wrapped

    return decorator

example.py

from datetime import timedelta
from flask import Flask, jsonify

from cache_control import cache_control

app = Flask(__name__)

@app.route("/")
@cache_control(max_age=timedelta(minutes=15), public=True)
def index():
    return jsonify(hello="world")

also see twiebe/Flask-CacheControl#8