Messaging patterns—designing reliable conversations

Patterns

• One-off for simple RPC.
• Ports for streams, long operations, or bi-directional updates.
• Pub/Sub for fan-out via a hub in the service worker.

Contracts & errors

Use a stable envelope with type, requestId, version, payload, and error. Add timeouts, bounded retries, and idempotency keys for at-least-once delivery.

{
  "type": "CATALOG/UPDATE_PRICE",
  "requestId": "req_9t7f",
  "version": 2,
  "payload": { "sku": "A123", "price": 19.99 },
  "error": null
}

Backpressure

• Queue, drop, or coalesce—never allow unbounded buffers.
• Set concurrency caps and apply jittered delays for fairness.

Versioning

• Include a protocol version in each envelope.
• Use capability checks to deprecate safely.