The Euphona Engine, as an API

1. Create the file and get an upload target

curl -X POST https://api.euphonaai.com/v1/files \
  -H "Authorization: Bearer $EUPHONA_API_KEY" \
  -H "Idempotency-Key: $(uuidgen)" \
  -H "Content-Type: application/json" \
  -d '{"filename":"take-07.wav","bytes":58210044,"content_type":"audio/wav"}'

{
  "id": "file_8Kd2mQ...",
  "object": "file",
  "status": "awaiting_upload",
  "upload": { "protocol": "...", "url": "https://files.euphonaai.com/...", "expires_at": "..." }
}

2. Send the bytes to files., not to us

# Read upload.protocol, do not assume one. The resumable mechanism is an
# implementation choice inside the contract and can change without a major
# version bump, which is exactly why it is a field and not documentation.

3. Watch the job

curl -N https://api.euphonaai.com/v1/jobs/job_4Rb.../events \
  -H "Authorization: Bearer $EUPHONA_API_KEY"

event: job.progress
data: {"status":"analyzing","stage":"analyze","progress":{"fraction":0.4}}

event: job.completed
data: {"status":"succeeded","result":{...},"metering":{"pool":"payg","charged_minutes":3.4}}

4. Reconcile against the job itself

curl https://api.euphonaai.com/v1/jobs/job_4Rb... \
  -H "Authorization: Bearer $EUPHONA_API_KEY"

{"id":"job_4Rb...","status":"succeeded","result":{...},
 "metering":{"pool":"payg","charged_minutes":3.4}}

# The job resource is the state machine's current truth: whatever a stream
# showed or missed, read it back before you act on it. A dropped SSE
# connection reconnects with Last-Event-ID and loses nothing.

Verifying a delivery (Node.js)

import { createHmac, timingSafeEqual } from "node:crypto";

// Pass the raw body exactly as it arrived: JSON parsed and serialised again
// is not the message that was signed.
export function verifyEuphonaSignature(rawBody, header, secret, now = Date.now() / 1000) {
  const parts = header.split(",").map((part) => part.trim().split("="));
  const t = Number(parts.find(([key]) => key === "t")?.[1]);
  const signatures = parts.filter(([key]) => key === "v1").map(([, value]) => value);
  if (!Number.isFinite(t) || Math.abs(now - t) > 300) return false;
  const expected = createHmac("sha256", secret).update(`${t}.${rawBody}`).digest();
  return signatures.some((value) => {
    const given = Buffer.from(value, "hex");
    return given.length === expected.length && timingSafeEqual(given, expected);
  });
}