`object
method environment : Nethttpd_engine.extended_async_environment
method req_state : Nethttpd_engine.engine_req_state
method schedule_accept_body :
on_request:(Nethttpd_engine.http_request_notification -> unit) ->
?on_error:(unit -> unit) -> unit -> unit
method schedule_finish : unit -> unit
method schedule_reject_body :
on_request:(Nethttpd_engine.http_request_notification -> unit) ->
?on_error:(unit -> unit) -> unit -> unit
end`