mod.js

// we use an interval tree to quickly query a large number of CIDR IP ranges.
// the naive approach takes ~7ms per query on my laptop, whereas this takes 0.2ms.

class IntervalNode {
	constructor(interval) {
		this.interval = interval; // interval is an object like {start: x, end: y}
		this.max = interval.end;
		this.left = null;
		this.right = null;
	}
}

class IntervalTree {
	constructor() {
		this.root = null;
	}
  
	insert(interval) {
		if (!this.root) {
			this.root = new IntervalNode(interval);
			return;
		}

		let node = this.root;
		// eslint-disable-next-line no-constant-condition
		while (true) {
			node.max = Math.max(node.max, interval.end);

			if (interval.start < node.interval.start) {
				if (!node.left) {
					node.left = new IntervalNode(interval);
					break;
				}
				node = node.left;
			} else {
				if (!node.right) {
					node.right = new IntervalNode(interval);
					break;
				}
				node = node.right;
			}
		}
	}

	query(point) {
		let node = this.root;
		while (node) {
			if (point >= node.interval.start && point <= node.interval.end) {
				return true;
			}

			if (node.left && point <= node.left.max) {
				node = node.left;
			} else {
				node = node.right;
			}
		}
		return false;
	}
}

let itree;

async function updateList() {
	let timeoutMs = 20000;
	const ipv4CidrRanges = await fetch('https://raw.githubusercontent.com/josephrocca/is-vpn/main/vpn-or-datacenter-ipv4-ranges.txt', {signal:AbortSignal.timeout(timeoutMs)}).then(r => r.text()).then(t => t.trim().split('\n'));
	itree = new IntervalTree();
	ipv4CidrRanges.map(ipv4CidrToRange).forEach(range => itree.insert(range));
}

await updateList();
setInterval(updateList, 1000*60*60*12); // fetch updated ip range list every 12 hours

function ipToBinary(ip) {
	return ip.split('.').reduce((acc, octet) => (acc << 8) + parseInt(octet, 10), 0);
}

function ipv4CidrToRange(cidr) {
	const [baseIp, subnetMask] = cidr.split('/');
	const ipBinary = ipToBinary(baseIp);
	const rangeStart = ipBinary;
	const rangeEnd = ipBinary | ((1 << (32 - subnetMask)) - 1);
	return {start:rangeStart, end:rangeEnd};
}

export function isVpn(ip) {
	const ipBinary = ipToBinary(ip);
	return itree.query(ipBinary);
}