class type http_request_notification =object..end
This object notifies the user that the request has fully arrived (including
 the body if accepted), and can now be responded. The environment is the
 same as in the request header notification, but the channels are now
 unlocked.
method req_state : engine_req_stateReturns the request processing state which is `Received_request at the
 moment when this notification is delivered.
method environment : extended_async_environmentThe request environment. See above.
method schedule_finish : unit -> unitSchedules that the request is finished. See above.