[EXTERNAL] fix(events): catch FileNotFoundException in openBufferedReader to prevent TOCTOU crash (#3704) contributed by @tsushanth

[tonidero]

Problem

Fixes #3696.

EventsFileHelper.readFile guards with fileIsEmpty() before opening the event store file, but FileHelper.openBufferedReader then calls FileInputStream(file) without re-checking existence. A concurrent flush/rotate that deletes ad_event_store.jsonl between fileIsEmpty() returning false and FileInputStream(file) throws an uncaught FileNotFoundException on the SDK background thread (PurchasesFactory$LowPriorityThreadFactory), crashing the app.

From the reporter: this is the #1 fatal crash on production builds using AdMob/AppLovin ad trackers, with ~53 crashes / ~52 affected users over 30 days, reproduced on Android 14–16.

Crash stack:

Fatal Exception: java.io.FileNotFoundException: .../event_store/ad_event_store.jsonl: open failed: ENOENT
    at FileHelper.openBufferedReader(FileHelper.kt:80)
    at FileHelper.readFilePerLines(FileHelper.kt:39)
    at EventsFileHelper.readFile(EventsFileHelper.kt:61)
    at EventsManager.getStoredEvents(EventsManager.kt:422)
    at EventsManager.flushNextBatch(EventsManager.kt:277)

Fix

Catch FileNotFoundException in openBufferedReader and treat a missing file as empty — the same semantics fileIsEmpty() uses — logging at DEBUG level. The same pattern is already used in removeFirstLinesFromFile (line 58).

} catch (e: FileNotFoundException) {
    debugLog { "FileHelper: file not found when trying to read: $filePath. Treating as empty." }
}

Also adds a regression test that calls readFilePerLines on a nonexistent path and asserts no exception propagates and the block receives an empty sequence.

Testing

• New unit test in FileHelperTest covers the missing-file path.
• Existing tests all still pass.

Contributed by @tsushanth in #3704

---

Note

Low Risk
Narrow I/O hardening with empty-read semantics; affects event/diagnostics file reads but reduces crash risk rather than changing happy-path behavior.

Overview
Fixes a production crash when the ad/event store file disappears between an existence check and opening it for read (e.g. concurrent flush/rotate on the SDK background thread).

FileHelper.openBufferedReader now wraps the FileInputStream open in a try/catch for FileNotFoundException, logs at debug, and does not invoke the read callback—same “missing file = empty” semantics as fileIsEmpty(), aligned with how removeFirstLinesFromFile already handled missing files at a higher layer.

Adds a FileHelperTest regression that reads a nonexistent path and asserts no exception and no lines. Removes an EventsFileHelperTest that expected a REMOVE_LINES_EXCEPTION debug event when clearing a missing file, since that path no longer surfaces FileNotFoundException from the reader.

^{Reviewed by Cursor Bugbot for commit 9419fba. Bugbot is set up for automated code reviews on this repo. Configure here.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.50%. Comparing base (ae737e8) to head (9419fba).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3719      +/-   ##
==========================================
- Coverage   80.54%   80.50%   -0.04%     
==========================================
  Files         400      400              
  Lines       16595    16598       +3     
  Branches     2370     2370              
==========================================
- Hits        13367    13363       -4     
- Misses       2291     2302      +11     
+ Partials      937      933       -4     

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