Flask

Getting Started

pip install vpndetection-flask

Requires Python 3.11 or newer.

You need an API key. Create one in the console; the free tier's allowance is counted per source address, and a server is a single source address, so a key is what makes this usable in production rather than optional.

from flask import Flask
from vpndetection_flask import VPNDetection

app = Flask(__name__)
VPNDetection(app, api_key=os.environ["VPNDETECTION_API_KEY"])

init_app(app) is supported for the application-factory pattern.

from vpndetection_flask import lookup


@app.route("/")
def index():
    found = lookup()
    return "Hello, VPN user" if found.result.is_vpn else "Hello"

By default nothing is blocked. Every request gets an answer and your own code decides what that means — which is usually what you want, because whether a VPN visitor is a problem depends entirely on what they are doing.

Blocking

Pass a block_condition and a matching request is answered with 403 and never reaches your code.

block_condition = {"is_vpn": True}

A condition is written in the shape of a result, keyed by the same names the API uses, and only the members you name are considered. That lets it reach the evidence, not just the flags:

{"is_vpn": True, "vpn": {"provider": "nordvpn"}}  # one provider
{"is_resproxy": True, "resproxy": {"hits": {"gte": 5}}}  # a numeric threshold
{"vpn": {"confidence": ["high", "medium"]}}  # any of these
[{"is_tor": True}, {"is_resproxy": True}]  # a list is OR

Values are matched by equality, strings without regard to case. A list means any-of. A dict of gte/gt/lte/lt compares numbers, and every bound you give must hold, so two of them are a range. Members set to False or None are ignored, so a condition states the signals you act on; one that constrains nothing would match every request, and is refused when the middleware is built rather than silently blocking all your traffic.

Replace the refusal with on_blocked.

Where the client address comes from

This is the setting that decides whether any of the above works, and it is the one thing only you can get right.

By default the extension uses request.remote_addr, which is the socket peer unless you have wrapped the app in werkzeug's ProxyFix. Behind a load balancer without it, every visitor looks like the load balancer — a datacenter address, so a hosting rule would block all of them. Adding ProxyFix is Flask's own answer and everything else here follows from it.

For an edge that writes the address into its own header, name the header:

from python_flask import header_ip_selector

ip_selector = header_ip_selector("CF-Connecting-IP")  # or True-Client-IP, or your own

xff_ip_selector() reads X-Forwarded-For directly. Be aware that the left-most entry is whatever the caller sent, because proxies append to that header — it is only trustworthy when an edge you control overwrites it. If you know how many proxies sit in front, count from the right instead: xff_ip_selector(1) is the address your nearest proxy saw.

Anything else, pass your own callable. It receives the request and returns an address.

If the address resolves to a private one, the middleware says so once through the vpndetection logger. That is expected on localhost and is the signal to fix your configuration anywhere else.

When a lookup fails

The request is let through, and the reason is recorded on the answer's error. Our outage should not become yours, so a network failure, an exhausted quota or a rejected key all fail open. Pass fail_closed=True to block instead. Private addresses are answered locally and never fail, so this will not lock you out in development.

Cost and latency

Answers are cached for an hour, so a returning visitor costs nothing, and private addresses never leave the process. A cache miss is one request to our API, bounded at 2.5 seconds by default and not retried — on a request path, failing open quickly beats holding a visitor while we try again. Both are adjustable, as is the cache, through a vpndetection client you build yourself and pass as client.

Skip what you do not care about:

skip = lambda request: request.path.startswith("/static")

Beyond a few million distinct visitors a day, stop calling the API per request: download the dataset and look addresses up locally instead.

Absent is not false

Only ip and is_vpn come back on every plan. A field your plan does not include is None, which means "not in your plan" rather than "checked, and no".

lookup().result.is_hosting  # None when your plan does not include it

A block_condition naming a member your plan does not serve can never match, so the middleware warns once instead of failing silently. Pass on_missing_field="raise" to make it an error.