fix: duplicate message - WPB-11435

[netbe]

WPB-11435 [iOS] All messages in a 1:1 conversation duplicated in iOS

Issue

On the legacy code, it happens message get processed multiple times.
It could be that in the following recursive method, because of a suspension point, the fetchNextEventsBatch fetch the same event before we actually delete it from the database and so reprocess it.

  private func process(
        with privateKeys: EARPrivateKeys?,
        _ consumeBlock: ConsumeBlock,
        firstCall: Bool,
        callEventsOnly: Bool

• Make EventDecoder an actor so it's always executed on the same queue.
• Safe guard the method with isProcessing so we don't process twice the same event.

Testing

1. on a conversation, run web spam messages
2. on the receiver side, send messages

Actual:
You'll see duplicate messages

Fix:
You'll get no duplicate messages

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Checklist

• Title contains a reference JIRA issue number like [WPB-XXX].
• Description is filled and free of optional paragraphs.
• Adds/updates automated tests.

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UI accessibility checklist

If your PR includes UI changes, please utilize this checklist:

• Make sure you use the API for UI elements that support large fonts.
• All colors are taken from WireDesign.ColorTheme or constructed using WireDesign.BaseColorPalette.
• New UI elements have Accessibility strings for VoiceOver.

[github-actions]

Test Results

    1 files      1 suites   1m 34s ⏱️
1 207 tests 1 206 ✅ 0 💤 1 ❌
1 207 runs  1 207 ✅ 0 💤 0 ❌

For more details on these failures, see this check.

Results for commit afaa539.

♻️ This comment has been updated with latest results.

[datadog-wireapp]

Datadog Report

Branch report: fix/duplicate-message
Commit report: 5584811
Test service: wire-ios-mono

✅ 0 Failed, 1108 Passed, 0 Skipped, 1m 34.68s Total Time

[jullianm]

LGTM, just one non blocking comment about events batch processing logic

[jullianm]

question(non-blocking): so if a second events batch wants to be processed while the first one is not finished yet, we discard it (early return). And I guess it will be processed again once the first is finished otherwise we'll lose that events batch, right ?

[jullianm]

Or maybe this logic only concerns the duplicated events since the function is recursive. Just checking that we don't lose any events along the way.

[netbe]

to be honest I am not sure, this might be not completely correct