Caption videos from a Replit app without slowing it down

const crypto = require("node:crypto");
const express = require("express");

const app = express();
const REELSDK = "https://api.reelsdk.com";

app.post("/api/captions", express.json(), async (req, res) => {
  try {
    const response = await fetch(`${REELSDK}/v1/captions?wait=0`, {
      method: "POST",
      headers: {
        Authorization: `Bearer ${process.env.REELSDK_KEY}`,
        "Content-Type": "application/json",
      },
      body: JSON.stringify({
        video_url: req.body.video_url,
        style: "bold",
        webhook_url: `${process.env.PUBLIC_URL}/webhooks/reelsdk`,
      }),
    });

    const { job, error } = await response.json();
    if (!response.ok) return res.status(response.status).json({ error });
    res.status(202).json({ id: job.id, status: job.status });
  } catch (error) {
    console.error("reelsdk request failed", error);
    res.status(502).json({ error: "render service unreachable" });
  }
});

app.post("/webhooks/reelsdk", express.raw({ type: "*/*" }), (req, res) => {
  const body = req.body.toString("utf8");
  if (!verifyReelSignature(req.get("Reel-Signature"), body, process.env.REELSDK_WEBHOOK_SECRET)) {
    return res.status(401).send("invalid signature");
  }

  const job = JSON.parse(body);
  console.log("reelsdk job finished", job.id, job.status, job.outputs.video);
  // Save job.status and job.outputs.video for job.id in your database here
  res.send("ok");
});

function verifyReelSignature(header, body, secret) {
  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 expected = crypto.createHmac("sha256", secret).update(`${parts.t}.${body}`).digest();
  return crypto.timingSafeEqual(expected, Buffer.from(parts.v1, "hex"));
}

app.listen(3000, "0.0.0.0");