chore: implement a/b test middleware

apps/web/abTest/middlewareFactory.ts

@@ -0,0 +1,45 @@
+import { getBucket } from "abTest/utils";
+import type { NextFetchEvent, NextMiddleware, NextRequest } from "next/server";
+import { NextResponse } from "next/server";
+import z from "zod";
+
+const ROUTE_MAP = new Map<string, boolean>([
+  ["/event-types", Boolean(process.env.APP_ROUTER_EVENT_TYPES_ENABLED)] as const,
+]);
+
+const FUTURE_ROUTES_OVERRIDE_COOKIE_NAME = "x-calcom-future-routes-override";
+const FUTURE_ROUTES_ENABLED_COOKIE_NAME = "x-calcom-future-routes-enabled";
+
+const bucketSchema = z.union([z.literal("legacy"), z.literal("future")]).default("legacy");
+
+export const abTestMiddlewareFactory =
+  (next: NextMiddleware): NextMiddleware =>
+  async (req: NextRequest, event: NextFetchEvent) => {
+    const { pathname } = req.nextUrl;
+
+    const override = req.cookies.has(FUTURE_ROUTES_OVERRIDE_COOKIE_NAME);
+
+    const enabled = ROUTE_MAP.has(pathname) ? (ROUTE_MAP.get(pathname) ?? false) || override : false;
+
+    if (pathname.includes("future") || !enabled) {
+      return next(req, event);
+    }
+
+    const safeParsedBucket = override
+      ? { success: true as const, data: "future" as const }
+      : bucketSchema.safeParse(req.cookies.get(FUTURE_ROUTES_ENABLED_COOKIE_NAME)?.value);
+
+    if (!safeParsedBucket.success) {
+      // cookie does not exist or it has incorrect value
+
+      const res = NextResponse.next();
+      res.cookies.set(FUTURE_ROUTES_ENABLED_COOKIE_NAME, getBucket(), { expires: 1000 * 60 * 30 }); // 30 min in ms
+      return res;
+    }
+
+    const bucketUrlPrefix = safeParsedBucket.data === "future" ? "future" : "";
+
+    const url = req.nextUrl.clone();
+    url.pathname = `${bucketUrlPrefix}${pathname}/`;
+    return NextResponse.rewrite(url);
+  };

apps/web/abTest/utils.ts

@@ -0,0 +1,9 @@
+import { AB_TEST_BUCKET_PROBABILITY } from "@calcom/lib/constants";
+
+const cryptoRandom = () => {
+  return crypto.getRandomValues(new Uint8Array(1))[0] / 0xff;
+};
+
+export const getBucket = () => {
+  return cryptoRandom() * 100 < AB_TEST_BUCKET_PROBABILITY ? "future" : "legacy";
+};

packages/lib/constants.ts

@@ -106,3 +106,4 @@ export const APP_CREDENTIAL_SHARING_ENABLED =
 
 export const DEFAULT_LIGHT_BRAND_COLOR = "#292929";
 export const DEFAULT_DARK_BRAND_COLOR = "#fafafa";
+export const AB_TEST_BUCKET_PROBABILITY = Number(process.env.AB_TEST_BUCKET_PROBABILITY) ?? 10;

turbo.json

@@ -324,6 +324,8 @@
     "ZOHOCRM_CLIENT_ID",
     "ZOHOCRM_CLIENT_SECRET",
     "ZOOM_CLIENT_ID",
-    "ZOOM_CLIENT_SECRET"
+    "ZOOM_CLIENT_SECRET",
+    "AB_TEST_BUCKET_PROBABILITY",
+    "APP_ROUTER_EVENT_TYPES_ENABLED"
   ]
 }