Render faceless shorts from a Worker and keep them in R2

{
  "name": "shorts",
  "main": "src/index.ts",
  "compatibility_date": "2026-10-01",
  "r2_buckets": [{ "binding": "VIDEOS", "bucket_name": "shorts" }]
}

npx wrangler r2 bucket create shorts

npx wrangler secret put REELSDK_KEY
npx wrangler secret put REELSDK_WEBHOOK_SECRET

npx wrangler deploy

interface Env {
  REELSDK_KEY: string;
  REELSDK_WEBHOOK_SECRET: string;
  VIDEOS: R2Bucket;
}

const REELSDK = "https://api.reelsdk.com";

export default {
  async fetch(request, env): Promise<Response> {
    const url = new URL(request.url);
    if (request.method !== "POST") return new Response("method not allowed", { status: 405 });

    if (url.pathname === "/shorts") {
      const { topic } = await request.json<{ topic: string }>();

      const res = await fetch(`${REELSDK}/v1/shorts?wait=0`, {
        method: "POST",
        headers: {
          Authorization: `Bearer ${env.REELSDK_KEY}`,
          "Content-Type": "application/json",
        },
        body: JSON.stringify({
          topic,
          duration_s: 45,
          style: "cinematic",
          webhook_url: `${url.origin}/reelsdk-webhook`,
        }),
      });

      return new Response(res.body, {
        status: res.status,
        headers: { "Content-Type": "application/json" },
      });
    }

    if (url.pathname === "/reelsdk-webhook") {
      const body = await request.text();
      const signature = request.headers.get("reel-signature");

      if (!(await verifyReelSignature(signature, body, env.REELSDK_WEBHOOK_SECRET))) {
        return new Response("invalid signature", { status: 401 });
      }

      const job = JSON.parse(body);
      if (job.status !== "succeeded") return new Response("ok");

      // We stream the mp4 straight into R2, the Worker never holds it in memory
      const video = await fetch(job.outputs.video);
      if (!video.ok) return new Response("download failed", { status: 502 });

      await env.VIDEOS.put(`shorts/${job.id}.mp4`, video.body, {
        httpMetadata: { contentType: "video/mp4" },
        customMetadata: { title: job.result?.title ?? "" },
      });
      return new Response("ok");
    }

    return new Response("not found", { status: 404 });
  },
} satisfies ExportedHandler<Env>;

async function verifyReelSignature(header: string | null, body: string, secret: string) {
  const parts = Object.fromEntries((header ?? "").split(",").map((part) => part.split("=")));
  const age = Math.abs(Date.now() / 1000 - Number(parts.t));
  if (!/^[0-9a-f]{64}$/i.test(parts.v1 ?? "") || !(age <= 300)) return false;

  const encoder = new TextEncoder();
  const key = await crypto.subtle.importKey(
    "raw",
    encoder.encode(secret),
    { name: "HMAC", hash: "SHA-256" },
    false,
    ["verify"],
  );
  const signature = Uint8Array.from(parts.v1.match(/../g), (pair: string) => parseInt(pair, 16));
  return crypto.subtle.verify("HMAC", key, signature, encoder.encode(`${parts.t}.${body}`));
}