sse-kafka Binding

Defines a binding with sse-kafka support, with proxy behavior.

proxy

Full config

The proxy kind sse-kafka binding adapts sse data streams into kafka data streams, so that kafka messages can be delivered to sse clients.

Filtering can be performed by kafka message key, message headers, or a combination of both message key and headers, extracting the parameter values from the inbound sse path.

Progress across kafka topic partitions is conveyed to the sse client via event id and when the stream is implicitly paused during sse client reconnect, the last-event-id header in the sse reconnect request contains the last received event id value, allowing the sse stream to resume reliable message delivery automatically.

The event id can be configured to include the message key and etag of each message, avoiding the need to duplicate the key in the message body and making it suitable for integration with http-kafka binding's use of etag for conditional if-match operations.

When a kafka tombstone (null value) message is received by the sse-kafka binding, it delivers a delete event to the sse client. This informs the client which specific message has been deleted by observing the message key from the sse delete event id.

sse_kafka_proxy:
  type: sse-kafka
  kind: proxy
  routes:
    - when:
        - path: /items
      exit: kafka_cache_client
      with:
        topic: items-snapshots
        event:
          id: '["${base64(key)}","${etag}"]'