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Message Processing

Overview

The worker consumes events from Kafka or NATS through Watermill and durably enqueues webhook deliveries before acknowledging each broker message.

Flow

Broker
  │
  ▼
Watermill handler
  ├─ unmarshal the event
  ├─ normalize the event type
  ├─ find matching active configs
  ├─ INSERT pending deliveries in one transaction
  └─ return after commit
        │
        ├─ success → broker ACK
        └─ error   → broker NACK

The handler never performs outbound HTTP. Endpoint latency therefore does not block broker ingestion.

deliveries has a unique (event_id, config_id) index. If the broker redelivers a message after an uncertain acknowledgement, ON CONFLICT DO NOTHING makes the enqueue operation idempotent.

Event format

Events are decoded as publish.EventMessage:

  • type is the event type matched against config filters;
  • app, when present, is prepended to the type;
  • idempotency_key is propagated to outbound webhook headers.

The normalized type is lowercase and formatted as <app>.<type> when app is present.

Transaction and acknowledgement contract

All matching deliveries are inserted in a single PostgreSQL transaction. The consumer returns success only after that transaction commits.

Failure Result
Invalid broker payload NACK
Config lookup failure NACK
Delivery insert or commit failure NACK
No matching active config ACK with no delivery
Existing (event_id, config_id) ACK after idempotent no-op

Once persisted, first attempts and retries are both handled by the dispatcher described in retry-mechanism.md.