OCPP, OCPP201: interface subscriptions happen too late

[barsnick]

Describe the bug

The OCPP201 module subscribes many (most) of the interface variables in its ready() function, probably due to dependencies on the Charger state machine.

This leads to the module potentially missing published variables from other modules, especially "early" infos such as EvseManager state changes and FirmwareUpdateNotifications.

This has been observed in real-life scenarios.

This also affects the OCPP module's system interface, while evse_manager and error seem to be handled properly there.

EVerest Domain

OCPP1.6, OCPP2.0.1

Affected EVerest Module

OCPP201 OCPP

To Reproduce

From a module providing the system interface, publish a firmware_update_status = Installed variable immediately in its ready().

Note how the OCPP201 (and probably OCPP) module never handles this variable, as it isn't subscribing yet, and therefore does not send the corresponding message to the CSMS.

Anything else?

This affects OCPP 2.0.1 requirement L01.FR.28.

This is a follow-up to EVerest/libocpp#758

The OCPP module (implementing OCPP 1.6) correctly (mostly) subscribes in init(), but queues all requests while the Charger is not yet running:

everest-core/modules/OCPP/OCPP.cpp

Lines 261 to 269 in e3eb4d9

	if (!this->started) {
	EVLOG_info << "OCPP not fully initialized, but received a session event on evse_id: " << evse_id
	<< " that will be queued up: " << session_event.event;
	std::scoped_lock lock(this->session_event_mutex);
	this->event_queue[evse_id].push(session_event);
	return;
	}
	this->process_session_event(evse_id, session_event);

Note that the OCPP module does not yet do this for the system interface:

everest-core/modules/OCPP/OCPP.cpp

Lines 607 to 618 in e3eb4d9

	// FIXME(kai): subscriptions should be as early as possible
	this->r_system->subscribe_log_status([this](types::system::LogStatus log_status) {
	this->charge_point->on_log_status_notification(log_status.request_id,
	types::system::log_status_enum_to_string(log_status.log_status));
	});
	this->r_system->subscribe_firmware_update_status(
	[this](types::system::FirmwareUpdateStatus firmware_update_status) {
	this->charge_point->on_firmware_update_status_notification(
	firmware_update_status.request_id,
	conversions::to_ocpp_firmware_status_notification(firmware_update_status.firmware_update_status));
	});