Building an idempotent receiver

This guide walks through show the reader how to dedupe on event_id so retries don’t cause double-processing.

What you need to know

• Key on event_id from the signed payload, not delivery_id.
• Use an insert-if-not-exists pattern (e.g., Postgres ON CONFLICT DO NOTHING on a unique constraint).
• Keep the seen-events table for at least 30 days (matches Harbor’s event retention).

Example

Python (Flask)

import psycopg
# Table: CREATE TABLE seen_events (event_id text PRIMARY KEY, seen_at timestamptz DEFAULT now());

def process(event):
    event_id = event["event_id"]  # from Harbor-Event-Id header or event body
    with psycopg.connect(DB_URL) as conn, conn.cursor() as cur:
        cur.execute(
            "INSERT INTO seen_events (event_id) VALUES (%s) ON CONFLICT DO NOTHING RETURNING event_id",
            (event_id,),
        )
        inserted = cur.fetchone() is not None
    if not inserted:
        # Duplicate — Harbor retried a delivery we already handled.
        return
    do_actual_work(event)

Go (net/http)

// Assumes a unique constraint on seen_events.event_id.
func process(db *sql.DB, event Event) error {
    res, err := db.Exec(
        "INSERT INTO seen_events (event_id) VALUES ($1) ON CONFLICT DO NOTHING",
        event.EventID,
    )
    if err != nil { return err }
    n, _ := res.RowsAffected()
    if n == 0 {
        return nil  // already processed
    }
    return doActualWork(event)
}