Idempotence

curl -X POST "https://attendbeacon.com/api/v1/events/b3ac0000-0000-4000-8000-000000000001/registrations" \
  -H "Authorization: Bearer $ATTENDBEACON_KEY" \
  -H "Idempotency-Key: 6f1c2a9e-4b7d-4c0f-8e3a-5b9d1c7e0f42" \
  -H "Content-Type: application/json" \
  -d '{ "ticketTypeId": "b3ac0006-0000-4000-8000-000000000001", "firstName": "Anna", "lastName": "de Vries", "email": "anna.devries@example.com" }'

const idempotencyKey = crypto.randomUUID();      // once per registration, kept for its retries

async function register(person) {
  for (let attempt = 1; ; attempt++) {
    try {
      const response = await fetch(`${base}/events/${eventId}/registrations`, {
        method: "POST",
        headers: { Authorization: `Bearer ${key}`, "Idempotency-Key": idempotencyKey, "Content-Type": "application/json" },
        body: JSON.stringify(person)
      });
      if (response.status < 500) return response;  // an answer: the first, or the first again
    } catch { /* the connection dropped: try again with the same key */ }
    if (attempt === 4) throw new Error("AttendBeacon did not answer.");
    await new Promise((resolve) => setTimeout(resolve, 2 ** attempt * 1000));
  }
}

var idempotencyKey = Guid.NewGuid().ToString();  // once per registration, kept for its retries

for (var attempt = 1; ; attempt++)
{
    using var request = new HttpRequestMessage(HttpMethod.Post, $"events/{eventId}/registrations") { Content = JsonContent.Create(person) };
    request.Headers.Add("Idempotency-Key", idempotencyKey);
    try
    {
        using var response = await client.SendAsync(request);
        if ((int)response.StatusCode < 500) return await response.Content.ReadFromJsonAsync<JsonElement>();
    }
    catch (HttpRequestException) { /* try again with the same key */ }
    if (attempt == 4) throw new InvalidOperationException("AttendBeacon did not answer.");
    await Task.Delay(TimeSpan.FromSeconds(Math.Pow(2, attempt)));
}

idempotency_key = str(uuid.uuid4())              # once per registration, kept for its retries

for attempt in range(1, 5):
    try:
        response = requests.post(
            f"{base}/events/{event_id}/registrations",
            headers={"Authorization": f"Bearer {key}", "Idempotency-Key": idempotency_key},
            json=person,
            timeout=30,
        )
        if response.status_code < 500:
            break                                 # an answer: the first, or the first again
    except requests.ConnectionError:
        pass                                      # try again with the same key
    time.sleep(2 ** attempt)

$idempotencyKey = [guid]::NewGuid().ToString()   # once per registration, kept for its retries
$headers["Idempotency-Key"] = $idempotencyKey
$body = $person | ConvertTo-Json

foreach ($attempt in 1..4) {
    try {
        $attendee = Invoke-RestMethod -Method Post -Uri "$base/events/$eventId/registrations" -Headers $headers -ContentType "application/json" -Body $body
        break
    } catch {
        if ($_.Exception.Response -and [int]$_.Exception.Response.StatusCode -lt 500) { throw }
        Start-Sleep -Seconds ([math]::Pow(2, $attempt))
    }
}