A/B testing with same-URL direct access

const NAME = "myExampleWorkersABTest";

export default {
	async fetch(req) {
		const url = new URL(req.url);

		// Enable Passthrough to allow direct access to control and test routes.
		if (url.pathname.startsWith("/control") || url.pathname.startsWith("/test"))
			return fetch(req);

		// Determine which group this requester is in.
		const cookie = req.headers.get("cookie");

		if (cookie && cookie.includes(`${NAME}=control`)) {
			url.pathname = "/control" + url.pathname;
		} else if (cookie && cookie.includes(`${NAME}=test`)) {
			url.pathname = "/test" + url.pathname;
		} else {
			// If there is no cookie, this is a new client. Choose a group and set the cookie.
			const group = Math.random() < 0.5 ? "test" : "control"; // 50/50 split
			if (group === "control") {
				url.pathname = "/control" + url.pathname;
			} else {
				url.pathname = "/test" + url.pathname;
			}
			// Reconstruct response to avoid immutability
			let res = await fetch(url);
			res = new Response(res.body, res);
			// Set cookie to enable persistent A/B sessions.
			res.headers.append("Set-Cookie", `${NAME}=${group}; path=/`);
			return res;
		}
		return fetch(url);
	},
};

const NAME = "myExampleWorkersABTest";

export default {
	async fetch(req): Promise<Response> {
		const url = new URL(req.url);
		// Enable Passthrough to allow direct access to control and test routes.
		if (url.pathname.startsWith("/control") || url.pathname.startsWith("/test"))
			return fetch(req);
		// Determine which group this requester is in.
		const cookie = req.headers.get("cookie");
		if (cookie && cookie.includes(`${NAME}=control`)) {
			url.pathname = "/control" + url.pathname;
		} else if (cookie && cookie.includes(`${NAME}=test`)) {
			url.pathname = "/test" + url.pathname;
		} else {
			// If there is no cookie, this is a new client. Choose a group and set the cookie.
			const group = Math.random() < 0.5 ? "test" : "control"; // 50/50 split
			if (group === "control") {
				url.pathname = "/control" + url.pathname;
			} else {
				url.pathname = "/test" + url.pathname;
			}
			// Reconstruct response to avoid immutability
			let res = await fetch(url);
			res = new Response(res.body, res);
			// Set cookie to enable persistent A/B sessions.
			res.headers.append("Set-Cookie", `${NAME}=${group}; path=/`);
			return res;
		}
		return fetch(url);
	},
} satisfies ExportedHandler;

import random
from urllib.parse import urlparse, urlunparse
from workers import Response, fetch, WorkerEntrypoint

NAME = "myExampleWorkersABTest"

class Default(WorkerEntrypoint):
	async def fetch(self, request):
		url = urlparse(request.url)
		# Uncomment below when testing locally
		# url = url._replace(netloc="example.com") if "localhost" in url.netloc else url

		# Enable Passthrough to allow direct access to control and test routes.
		if url.path.startswith("/control") or url.path.startswith("/test"):
			return fetch(urlunparse(url))

		# Determine which group this requester is in.
		cookie = request.headers.get("cookie")

		if cookie and f'{NAME}=control' in cookie:
			url = url._replace(path="/control" + url.path)
		elif cookie and f'{NAME}=test' in cookie:
			url = url._replace(path="/test" + url.path)
		else:
			# If there is no cookie, this is a new client. Choose a group and set the cookie.
			group = "test" if random.random() < 0.5 else "control"
			if group == "control":
				url = url._replace(path="/control" + url.path)
			else:
				url = url._replace(path="/test" + url.path)

			# Reconstruct response to avoid immutability
			res = await fetch(urlunparse(url))
			headers = dict(res.headers)
			headers["Set-Cookie"] = f'{NAME}={group}; path=/'
			return Response(res.body, headers=headers)

		return fetch(urlunparse(url))

import { Hono } from "hono";
import { getCookie, setCookie } from "hono/cookie";

const app = new Hono();

const NAME = "myExampleWorkersABTest";

// Enable passthrough to allow direct access to control and test routes
app.all("/control/*", (c) => fetch(c.req.raw));
app.all("/test/*", (c) => fetch(c.req.raw));

// Middleware to handle A/B testing logic
app.use("*", async (c) => {
	const url = new URL(c.req.url);

	// Determine which group this requester is in
	const abTestCookie = getCookie(c, NAME);

	if (abTestCookie === "control") {
		// User is in control group
		url.pathname = "/control" + c.req.path;
	} else if (abTestCookie === "test") {
		// User is in test group
		url.pathname = "/test" + c.req.path;
	} else {
		// If there is no cookie, this is a new client
		// Choose a group and set the cookie (50/50 split)
		const group = Math.random() < 0.5 ? "test" : "control";

		// Update URL path based on assigned group
		if (group === "control") {
			url.pathname = "/control" + c.req.path;
		} else {
			url.pathname = "/test" + c.req.path;
		}

		// Set cookie to enable persistent A/B sessions
		setCookie(c, NAME, group, {
			path: "/",
		});
	}

	const res = await fetch(url);

	return c.body(res.body, res);
});

export default app;