[A/B Testing] Next.js - provider-agnostic KV adapter (Vercel KV + Upstash Redis)

[kuuak]

Context

Part of # A/B Testing for Superstack.111

What to build

A provider-agnostic KV adapter for reading/writing the A/B experiment registry from edge middleware. Must support Vercel KV (Vercel deployments) and Upstash Redis (self-hosted deployments).

Interface

// next/src/lib/kv/types.ts
interface KVAdapter {
  get<T>(key: string): Promise<T | null>;
  set(key: string, value: unknown, ttl?: number): Promise<void>;
  del(key: string): Promise<void>;
}

Implementations

• src/lib/kv/adapters/vercel-kv. uses @vercel/kvts
• src/lib/kv/adapters/upstash. uses @upstash/redis (REST API, edge-compatible)ts

Factory

src/lib/kv/index.ts selects the adapter based on NEXT_PUBLIC_KV_PROVIDER=vercel|upstash env var, with auto-detection fallback.

Environment variables

Variable	Required by
NEXT_PUBLIC_KV_PROVIDER	Factory (adapter selection)
UPSTASH_REDIS_REST_URL	Upstash adapter
UPSTASH_REDIS_REST_TOKEN	Upstash adapter
Vercel KV vars	Set automatically by Vercel dashboard

Edge runtime requirement

Both adapters must be compatible with the Next.js Edge runtime (no Node.js APIs).

Files to create

next/src/lib/kv/
 types.ts
 index.ts              # Adapter factory
 adapters/
 vercel-kv.ts    
 upstash.ts