Idempotency

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On the way in

{ "status": "duplicate", "message": "already accepted" }

curl -X POST https://hooksnode.com/p/<source-id> \
  -H "X-Idempotency-Key: order_9311_paid" \
  -d '{"event":"order.paid","order_id":"9311"}'

• The key is stored on the project. When the event has a source, the stored key is prefixed with that source, so the same header on another source is a new event.
• A key longer than 255 characters is stored as sha256: plus the hex SHA-256 of the full key. That stored form still dedupes.
• Use an ID that your system already has, such as the provider’s event ID.
• A CloudEvents id is a second dedupe key. Repeating that id is a duplicate even when X-Idempotency-Key is new.

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On the way out

1. Find a stable ID in the event. For example, Paystack’s data.reference, the email’s message.id, or the bank event’s email.id.
2. Before you do the work, check if you already did it for that ID.
3. Store the ID in the same database transaction as the work.

INSERT INTO processed_events (event_id) VALUES ($1)
ON CONFLICT (event_id) DO NOTHING
RETURNING event_id;
-- No row back: you already handled it. Answer 200 and stop.