Bugfix FXIOS-8105 [v121] Fix Send to Device failing intermittently

[mattreaganmozilla]

📜 Tickets

Jira ticket
Github issue

💡 Description

Fix for an intermittent bug that can cause Send to Device to fail. The issue appears to be a potential race between the UI setup code and the RustFXAccounts startup(). There are a few different solutions we can explore for addressing this; the approach here was the most straightforward solution I could find with the current info I have. This area could likely use additional discussion, particularly with UX/UI teams, to revisit how we're handling situations like this where we need to accommodate for possible delays in code that is required before the user can take certain share actions.

📝 Checklist

You have to check all boxes before merging

• Filled in the above information (tickets numbers and description of your work)
• Updated the PR name to follow our PR naming guidelines
• Wrote unit tests and/or ensured the tests suite is passing
• When working on UI, I checked and implemented accessibility (minimum Dynamic Text and VoiceOver)
• If needed I updated documentation / comments for complex code and public methods

[mobiletest-ci-bot]

	Messages
📖	Project coverage: 33.37%
📖	Edited 1 files
📖	Created 0 files

ShareTo.appex: Coverage: 34.44

File	Coverage
ShareViewController.swift	0.0%	⚠️

Generated by 🚫 Danger Swift against 4849335

[tarikeshaq]

+1 that we should review the whole FxA-in-extensions more wholisticly, but this does seem okay to me to fix the regression from the sync/FxA perspective - I defer the approval to an iOS engineer since there is ui code here

[tarikeshaq]

Do we know how this can be not nil? Is there a sequence of events where the ShareViewController is made in a context where the initialization already happened? I’m mostly curious nothing is functionally off here!

[mattreaganmozilla]

@tarikeshaq (cc @OrlaM) Just answering based on observation, there is a lot going on with this code that I still don't have full context/familiarity with. But what I could see was:

• The accountManager starts off as nil until startup() completes
• Startup is an async process and so there are potential races/timing issues
• Repeated shares in Safari will reload the UI components but RustFirefoxAccounts.shared.accountManager is non-nil if startup() has already previously completed (unless, presumably, the app extension is jetsammed or terminated by the OS etc.)

I observed that in some situations the accountManager was also seemingly non-nil when I would expect it to be nil (on an initial test of the extension etc.). However I can't say for certain if this was simply due to side effects of how I was testing.

I should also add that I still am not entirely certain what the original bug reporters were actually seeing since at the time of the fix there were no reliable repro steps or screen captures. But based on all the available info this is, AFAICT, the most likely cause of the issue and if so should hopefully correct it.

LMK if any further questions, I'm happy to investigate or dig into this further.

[tarikeshaq]

Repeated shares in Safari will reload the UI components but RustFirefoxAccounts.shared.accountManager is non-nil if startup() has already previously completed (unless, presumably, the app extension is jetsammed or terminated by the OS etc.)

Ahh that makes a ton of sense, thanks a ton @mattreaganmozilla - really appreciate you digging into this one!!

[OrlaM]

@Mergifyio backport release/v121 release/v122

[mergify]

backport release/v121 release/v122

✅ Backports have been created

• #18049 Bugfix FXIOS-8105 [v121] Fix Send to Device failing intermittently (backport #18042) has been created for branch release/v121
• #18050 Bugfix FXIOS-8105 [v121] Fix Send to Device failing intermittently (backport #18042) has been created for branch release/v122