fastify-floc-off/src/index.js

Fastify plugin to opt out of Google's Topics advertising-surveillance API

"use strict";

const fp = require("fastify-plugin");

/**
 * @author Frazer Smith
 * @description Simple plugin that adds an `onRequest` hook to opt out of Google's FLoC
 * advertising-surveillance network by setting/adding the "interest-cohort=()" directive
 * to the Permissions-Policy response header.
 * @param {import("fastify").FastifyInstance} server - Fastify instance.
 */
async function fastifyFlocOff(server) {
	server.addHook("onRequest", async (_req, res) => {
		const header = res.getHeader("Permissions-Policy");

		/**
		 * Headers can be returned as an array.
		 * @see {@link https://nodejs.org/docs/latest/api/http.html#requestsetheadername-value | Node.js HTTP API}
		 */
		if (Array.isArray(header)) {
			header.push("interest-cohort=()");
			res.header("Permissions-Policy", header);
			return;
		}

		if (header) {
			res.header("Permissions-Policy", `${header}, interest-cohort=()`);
		} else {
			res.header("Permissions-Policy", "interest-cohort=()");
		}
	});
}

module.exports = fp(fastifyFlocOff, {
	fastify: "5.x",
	name: "fastify-floc-off",
}); // CommonJS export
module.exports.default = fastifyFlocOff; // ESM default export
module.exports.fastifyFlocOff = fastifyFlocOff; // TypeScript and named export