FXIOS-731 ⁃ HTTP HEAD etags to cut down on data requests from Breach Alerts

[vphong]

Relates to #6960. Caches breach data using FileManager; creates a new BreachAlertsClient function fetchEtag that specifically gets the Etag from the header of a given endpoint.

When loadBreaches is called:

• If a breaches.json file exists:
  1. loads data from that file
     • if at least 3 days have passed since the file was last updated from the internet as saved in Profile.prefs
       1. refetch the data
       2. save the etag and date from the endpoint's header in user's Profile.prefs
       3. delete the old breaches.json to avoid data collisions and save the new data as breaches.json
     • else update the date and use data from local file
  2. decode the data and hand it off to a completion block
• else:
  • fetch data from the Monitor endpoint
  • save the etag and date from the endpoint's header in user'sProfile.prefs
  • save data as breaches.json

┆Issue is synchronized with this Jira Task

[mozillamobilebot]

SwiftLint found issues

Warnings

File	Line	Reason
LoginListViewModel.swift	30	Prefer empty collection over optional collection. (discouraged_optional_collection)
LoginListViewModel.swift	101	Prefer empty collection over optional collection. (discouraged_optional_collection)

Sentry check list

• I understand that only .fatal events will be reported on release

• The message param contains a string that will not create multiple events

Generated by 🚫 Danger

[garvankeeley]

Looking great, almost there. This is inherently tricky stuff, so I might be extra-pendantic, so please bear with me!
I'll ping you on slack.

[garvankeeley]

guard instead of if pls

[vphong]

This if is part of an if/else so is guard still necessary? else:

firefox-ios/Client/Frontend/Login Management/BreachAlertsManager.swift

Lines 81 to 85 in 2090439

	} else {
	// first time loading breaches, so fetch as normal and hand off
	self.fetchAndSaveBreaches(completion)
	}
	}

Not sure if guard would make it more readable but open to suggestions of course

[kaylagalway]

All good on my end. Thanks for the changes- great work here!

[kaylagalway]

Thanks! Looks good!

[garvankeeley]

remove the mocks pls