Allows to pluck events for one or more topics and remove them from the current payload. The removed — siphoned — events are sent to a siphon module that must implement the call/1 function, that will be invoked with a list of Routemaster.Drain.Event structures as argument.

The siphons’ call/1 function is invoked in a supervised Task, so all siphons are to be considered asynchronous and independent.

This drain plug is very similar to the Routemaster.Drains.Notify module, with the difference that it modifies the event list in the current payload before passing it downstream to the next drain in the pipeline.

It’s meant to be used when some topic should not be processed with the rest of the drain pipeline, and you want to extract it from the stream before it reaches the next drains. A common use case is when you care about every single event for a topic (e.g. fast changing resources where each event carries a data payload), and these need to be processed separately before a Routemaster.Drains.Dedup or Routemaster.Drains.IgnoreStale drain can discard any of them.

Options

• :topic (or :topics, plural): either a binary or a list of binaries. This is the topic or topics that will be removed from the current payload and sent to the siphon module.
• :to: the siphon module that will receive the events.

Examples

alias Routemaster.Drains.Siphon

drain Siphon, topic: "burgers", to: BurgerSiphon
drain Siphon, topics: ~w(coke fanta), to: DrinksSiphon