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Hooks into Coaches ActiveSupport notification to instrument middleware using Skylight
# Coach emits profiling notifications via ActiveSupport. SkylightMiddlewareLogger
# listens for these events and logs request data via Skylight.
class SkylightMiddlewareLogger
def self.log!
@instance ||= new.log!
end
def log!
# Tell Coach to start issuing ActiveSupport::Notifications
Coach::Notifications.subscribe!
subscribe('handler.start') { |*_, event| log_handler_start(event) }
subscribe('middleware.start') { |*_, event| log_middleware_start(event) }
subscribe('middleware.finish') { |*_, event| log_middleware_finish(event) }
subscribe('handler.finish') { |*_, event| log_handler_finish(event) }
self
end
private_class_method :new
private
def initialize
@requests = {}
end
def subscribe(event, &block)
ActiveSupport::Notifications.subscribe("coach.#{event}", &block)
end
# Fetches the current trace from Skylight gem
def skylight_trace
Skylight::Instrumenter.instance.try(:current_trace)
end
def traces_for_request(event)
@requests[event[:request].uuid]
end
def log_handler_start(event)
trace = skylight_trace
return unless trace.present?
# Skylight requires setting of the endpoint name in order to create a new request
# trace.
trace.endpoint = event[:middleware]
@requests[event[:request].uuid] = {
exec: trace.instrument('app.block', 'Exec'), # entire chain trace
chain_traces: {} # collection of traces for each middleware
}
end
def log_middleware_start(event)
trace = skylight_trace
return unless trace.present?
# Create and store a Skylight trace for this middleware under the current request.
# This allows retrieval and termination of this request on middleware.finish.
middleware_trace = trace.instrument('app.block', event[:middleware])
traces_for_request(event)[:chain_traces][event[:middleware]] = middleware_trace
end
def log_middleware_finish(event)
trace = skylight_trace
return unless trace.present?
# Terminate this middlewares trace and remove from the request chain
chain_traces = traces_for_request(event)[:chain_traces]
trace.done(chain_traces.delete(event[:middleware]))
end
def log_handler_finish(event)
trace = skylight_trace
return unless trace.present?
# Terminate the request trace and remove from the request cache
trace.done(@requests.delete(event[:request].uuid)[:exec])
end
end
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