flask-useragent

flask-useragent gives one the ability to create functions, that are only triggered by flask if the URL and the useragent matches.

Why does it exist?

This project was inspired by this twitterthread. It is just a funny sideproject, please don't use this project in any serious environment.

The task can be easily solved with the following code:

from flask import Flask
from flask import request

app = Flask(__name__)


@app.route("/")
def main_page():
    user_agent = request.headers.get("User-Agent")

    if "curl" in user_agent:
        return "you used curl"

    if "Mozilla" in user_agent:
        return "you used a firefox based browser"

    return f"{user_agent}"


if __name__ == "__main__":
    app.run(debug=True)

However, while solving this task, I wondered if it would be possible to solve it with the route()-Decorator which lead me to write flask-useragent.

With it, the above example can be written as:

from flask import request
from flask import Flask
from flask_useragent import FlaskUserAgent


app = Flask(__name__)
ua_app = FlaskUserAgent(app)


# This should match user-agents used by curl
@ua_app.ua_route("/", user_agent=r"curl\/[0-9.]+")
def curl_endpoint():
    return "you use curl"


# This should match user-agents used by Mozilla Firefox
@ua_app.ua_route("/", user_agent="Mozilla[.a-zA-Z0-9/ ();_:]+")
def firefox_endpoint():
    return "you used a firefox based browser"


# This function is used as a fallback function in case either curl nor
# Firefox is being used
@ua_app.fallback("/")
def fallback_endpoint():
    user_agent = request.headers.get("User-Agent")
    return f"{user_agent}"


if __name__ == "__main__":
    app.run(debug=True)

Usage

---

flask-useragent works just like flask, except that it provides two new Functiondecorator.

ua_route

This Decorator can be used to restrict the underlying function to a certain user-agent. It expects a keyword_argument called user_agent. The provided string can be a regex expression or a full user-agent-string.

If there are a regex-string that would match and a exact one, the exact one will be used.

The following example shows how to use the ua_route Decorator

from flask import Flask
from flask import request
from flask_useragent import FlaskUserAgent

app = Flask(__name__)
ua_app = FlaskUserAgent(app)

# This uses a specific user-agent-string 
@ua_app.ua_route("/", user_agent=r"curl/7.82.0")
def curl_endpoint_7_82_0():
    return "you use curl 7.82.0"


# This uses a regex-string as user-agent
@ua_app.ua_route("/", user_agent=r"curl\/[0-9.]+")
def curl_endpoint():
    return "you use curl"


if __name__ == "__main__":
    app.run(debug=True)

fallback

this Decorater can be used to donate, that the underlying function should be used in case the useragent does not match the user-agent-string of the other functions.

from flask import Flask
from flask import request
from flask_useragent import FlaskUserAgent

app = Flask(__name__)
ua_app = FlaskUserAgent(app)


@ua_app.ua_route("/", user_agent=r"curl\/[0-9.]+")
def curl_endpoint():
    return "you use curl"


@ua_app.fallback("/")
def fallback_endpoint():
    user_agent = request.headers.get("User-Agent")
    return f"{user_agent}"


if __name__ == "__main__":
    app.run(debug=True)

TODOs and Problems

Currently, flask-useragent does not support:

• HTTP Methodes