Implement SSE background updates for Field Reports

[srabraham]

We've never actually had SSEs set up for Field Reports, as I observed here:

ranger-ims-server/src/ims/element/static/ims.js

Lines 1001 to 1007 in 1f75de5

	// TODO: this will never receive any events currently, since the server isn't configured to
	// fire events for FieldReports. See
	// https://github.com/burningmantech/ranger-ims-server/blob/954498eb125bb9a83d2b922361abef4935f228ba/src/ims/application/_eventsource.py#L113-L135
	eventSource.addEventListener("FieldReport", function(e) {
	const send = new BroadcastChannel(fieldReportChannelName);
	send.postMessage(JSON.parse(e.data));
	}, true);

and that's because this "if-else" doesn't have an "else if" case for FieldReport:

ranger-ims-server/src/ims/application/_eventsource.py

Lines 115 to 142 in 1f75de5

	if eventClass is Incident:
	incident = loggerEvent.get("incident", None)
	if incident is None:
	incidentNumber = loggerEvent.get("incidentNumber", None)
	eventName = loggerEvent.get("eventID", "")
	else:
	incidentNumber = incident.number
	eventName = incident.eventID
	if incidentNumber is None:
	self._log.critical(
	"Unable to determine incident number from store event: {event}",
	event=loggerEvent,
	)
	return None
	message = {
	"event_id": eventName,
	"incident_number": incidentNumber,
	}
	else:
	self._log.critical(
	"Unknown data store event class {eventClass} sent event: {event}",
	eventClass=eventClass,
	event=loggerEvent,
	)

[srabraham]

There are a few subtleties here that make me more nervous about implementing SSEs for Field Reports than for Incidents.

1. This would increase the number of SSE calls on playa, i.e. since anyone with writeFieldReports permission would start having an SSE too (previously it'd just be people with writeIncident or readIncident). Load problem? Probably not, but who knows for sure.
2. I made a sweet optimization today to the Incidents page, so that it only updates data on a per-Incident basis based on SSEs (rather than always updating the entire page). That optimization doesn't carry over perfectly to the Field Reports page, since Rangers with limited IMS access (i.e. most Rangers) get 403 errors when they try to access FRs to which they don't have access. Those 403s end up showing as JS errors in the web browser, and there seems to be no good way to prevent that. It's ugly seeing constant errors!

I may work on the first point above by having an IMS page automatically redirect a page to the IMS homescreen when the user is logged out. That'd end the open SSE connection.

[srabraham]

With #1523 in place, we're now updating the Field Reports and Field Report pages on any updates to a Field Report.

Here's where we are:

• Publish SSEs on updates to Field Reports add SSEs for Field Report updates, listen for them from frontend #1523
• Update Field Report page when the in-scope FR has been updated add SSEs for Field Report updates, listen for them from frontend #1523
• Update Field Reports page when any FR has been updated add SSEs for Field Report updates, listen for them from frontend #1523

Here's where I might take this next:

• Update Incident page when an FR currently attached to that incident has been updated
• Update Incident page when any FR is updated, but just update that one FR, don't fetch all (for efficiency)

And this is an option, but not one I'm considering all that strongly:

• Update the Incidents page's indexed list of FRs anytime any FR changes (this would require a fair bit of background work on any FR update, and it would be done solely to feed the text-search feature. IMO the cost might outweigh the benefits)

[srabraham]

I'm ready to call this done