A controller with the stream it controls.
This controller allows sending data, error and done events on its stream. This class can be used to create a simple stream that others can listen on, and to push events to that stream.
It's possible to check whether the stream is paused or not, and whether it has subscribers or not, as well as getting a callback when either of these change.
event
. [...]
source
and puts them into this controller's stream. [...]