moleculer-event-callback

As Moleculer events are fire-and-forget, this project works around this by providing event subscribers a way to send their answers back to the event emitter.

This project is necessary until Moleculer channels are production ready. Contrary to Moleculer events, channels provides a way to send reliable messages. Here "reliable" means that the message emitter knows how its message was handled by the subscribers. Two helpers are provided in order to implement this feature:

• On the emitter side, the callEventMixin mixin adds a callback action and a $$callEvent method to the service. $$callEvent emits a Moleculer event with an $$eventReturnHandler parameter. This parameter keeps information about the emitter callback action.

• On the subscriber side, the callEventReturnDecorator function decorates a Moleculer event schema specification. The decorator ensures that the subscriber's event handler returned value or raised error is sent back through the emitter callback action.

For a code example, see the following unit test.