Create a reduced REST API with Upstash and Nextjs App Router and optional catch-all segments

[[...slug]].ts

// /app/api/upstash/[[...slug]].ts
import { Redis } from "@upstash/redis";

const redis = Redis.fromEnv();

type Params = { slug: string | string[] | undefined };

function createKey(slug: Params["slug"]) {
  return slug ? [...(Array.isArray(slug) ? slug : [slug])].join(":") : "_root";
}

export async function GET(_: Request, { params }: { params: Params }) {
  const key = createKey(params.slug);
  const state = await redis.json.get(key);
  return new Response(JSON.stringify(state), {
    status: 200,
    headers: { "Content-Type": "application/json" },
  });
}

export async function POST(request: Request, { params }: { params: Params }) {
  const json = await request.json();
  const key = createKey(params.slug);
  await redis.json.set(key, "$", JSON.stringify(json));
  return new Response("Created", { status: 201 });
}

export async function PUT(request: Request, { params }: { params: Params }) {
  const { name, value } = await request.json();
  const key = createKey(params.slug);
  try {
    await redis.json.set(key, `$.${name}`, JSON.stringify(value));
  } catch {
    // UpstashError: ERR new objects must be created at the root
    await redis.json.set(key, "$", { [name]: JSON.stringify(value) });
  }
  return new Response("Updated", { status: 201 });
}

export async function DELETE(request: Request, { params }: { params: Params }) {
  const key = createKey(params.slug);
  await redis.del(key);
  return new Response("Deleted", { status: 200 });
}

How to call it:

export async function createState() {
  return await fetch("/api/v1/upstash/state", {
    method: "POST",
    headers: {
      "Content-Type": "application/json",
    },
    body: JSON.stringify({
      title: "Hello World",
      status: "Ready",
    }),
  });
};

export async function getState() {
  return await fetch("/api/v1/upstash/state");
};

export async function updateState() {
  return await fetch("/api/v1/upstash/state", {
    method: "PUT",
    headers: {
      "Content-Type": "application/json",
    },
    body: JSON.stringify({
      name: "title",
      value: "New World",
    }),
  });
};

export async function deleteState() {
  return await fetch("/api/v1/upstash/state", {
    method: "DELETE",
  });
};