Observers are blocks that are notified about state changes during a request's lifetime. Keep in mind that the active state is set every ~1s, so you'll be notified every time.
You can register an observer with:
Rack::Timeout.register_state_change_observer(:a_unique_name) { |env| do_things env }There's currently no way to subscribe to changes into or out of a particular state. To check the actual state we're moving into, read env['rack-timeout.info'].state. Handling going out of a state would require some additional logic in the observer.
You can remove an observer with unregister_state_change_observer:
Rack::Timeout.unregister_state_change_observer(:a_unique_name)rack-timeout's logging is implemented using an observer; see Rack::Timeout::StateChangeLoggingObserver in logging-observer.rb for the implementation.
Custom observers might be used to do cleanup, store statistics on request length, timeouts, etc., and potentially do performance tuning on the fly.