1. How Downlink Works

• subscription name: ng-gateway-plugin-{app_id} (Stable naming, easy for broker to maintain state)
• subscription type: Shared
• topics: Exact topic list from route table

WARNING

Downlink topic does not support template/wildcard/regex.

---

2. AckPolicy / FailurePolicy

Pulsar confirmation semantics:

• ack_policy=never: No ack
• ack_policy=always: Always ack (Bad messages will be discarded)
• ack_policy=on_success:
  • Successfully converted to event, or ignored by filter (Ok(None)) → ack
  • Failure:
    • failure_policy=drop → ack (Discard)
    • failure_policy=error → nack (Wait for retry/redelivery)

See: Downlink Overview

---

3. Payload Mode

• Recommended: EnvelopeJson (event.kind routable, suitable for mixed topic)
• Platform shape inconsistent: MappedJson + filter

Entry:

• Downlink EnvelopeJson
• Downlink MappedJson + Filter