class http_engine :This engine processes the requests arriving on the file descriptor using the Unix event system. Whenever a new request header arrives, the functionon_request_header:(http_request_header_notification -> unit) -> unit -> #http_engine_config -> Unix.file_descr -> Unixqueue.unix_event_system ->[unit]Uq_engines.engine
on_request_header is called back, and must handle the request.
Unless aborted using the abort method, this engine is always successful.
Errors are logged, but not returned as result.
The file descriptor is closed after processing all HTTP requests and responses. It is also closed on error and when the engine is aborted.
An aborted engine does not try to clean up resources external to the
engine, e.g. by calling the on_error functions. This is up to the user.
