Prevent duplicate Storage requests on resume

[dajiaohuang]

Summary

• Prevent duplicate upload/download setup from immediate resume or pause/resume by rejecting obsolete enqueue generations before preparation and fetcher installation.
• Cover public putData/getData followed by immediate resume without pause, and download resume from its progress callback while completion is held.
• Correct the upload object-path fixture, bound XCTest waits, release test gates on teardown, and synchronize discard observation at all setup stages.
• Update Unreleased changelog with Prevent duplicate Storage requests on resume #16771.

Validation

• Four changed Swift files pass pinned SwiftFormat 0.55.5 lint and git diff --check.
• Actual FirebaseStorageUnit/StorageTaskEnqueueTests on Xcode 26.4.1 and an iOS simulator: all five tests passed, zero failures, at source 3b0555b. This includes immediate upload/download resume, discarded earlier setup, and resume during download progress.
• Native XCTest run uses the repository Swift Package test setup and real GTMSessionFetcher callbacks. The progress case controls internal progress state to avoid a transient-state timing dependency. This is focused class coverage; the full platform matrix remains separate.

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[paulb777]

Thanks for the contribution! A few housekeeping items:

• CHANGELOG: The entry in FirebaseStorage/CHANGELOG.md is under # 12.19.0, which has already shipped. Please move it under a # Unreleased heading at the top of the file (add the heading if it isn't there yet).
• PR number: end the entry with this PR's number, e.g. - [fixed] Description. (#16771).
• Formatting: after updating, please run scripts/style.sh so the infra.check job passes. It needs clang-format 23 and swiftformat (see scripts/setup_check.sh). If you can't run it locally, the infra.check log lists the files that need formatting.

[paulb777]

/gemini review

[gemini-code-assist]

Code Review

This pull request prevents duplicate upload and download requests when resuming a task before its initial setup completes by introducing generation tracking (enqueueGeneration) in StorageDownloadTask and StorageUploadTask. Unit tests have been added to verify that earlier setups are discarded upon resumption. The review feedback highlights a potential data race in both task implementations where setupDiscardedHandlerForTesting is accessed outside of the lock, and suggests synchronizing this access by retrieving the handler under the lock before executing it.

[paulb777]

Thanks, this is easy to hit: putData(...) already enqueues, so an immediate resume() (or a quick pause()/resume()) runs setup twice and starts two fetchers, orphaning the first. The generation approach looks sound to me.

CI confirms one blocker: testUploadResumeDiscardsEarlierSetup crashes with Fatal error: Internal error enqueueing a Storage task in the SPM unit tests (e.g. spm (xcode-27, catalyst)). The cause is inline.

Coverage: please add tests for the most likely real-world trigger (putData(...).resume() and getData(...).resume() right after creation, with no pause()), and for download resume() during .progress.

[dajiaohuang]

Fixed the upload fixture to use child("object"), avoiding the nil metadata path. Both initial-setup and discard waits now use XCTest expectations with 10-second async fulfillment; teardown releases the service gate even after a timeout. Added immediate putData(...).resume() and getData(...).resume() variants without pause, plus a real download fetcher/progress-callback test that holds completion while exercising resume in a deterministic progress state and checks that only one request starts.

The discard handler now has stateLock-protected storage; notification copies the handler under the lock and invokes it outside the lock. Both task types notify at all three setup-discard stages (before preparation, after service acquisition, and before fetcher installation). Moved the changelog under Unreleased/#16771. Four-file pinned SwiftFormat 0.55.5 lint and git diff --check pass. The new Apple/GTMSessionFetcher XCTest coverage has not run on this Windows host; current-head native CI remains required.

[paulb777]

/gemini review

[gemini-code-assist]

Code Review

This pull request prevents duplicate upload and download requests when resuming a task before its initial request setup has completed. It introduces an enqueueGeneration counter in both StorageDownloadTask and StorageUploadTask to track and discard obsolete setup tasks, and adds corresponding unit tests to verify this behavior. No review comments were provided, so there is no additional feedback.

[dajiaohuang]

The revised tests now run in the repository's actual Swift Package test target. At source 3b0555b, all five StorageTaskEnqueueTests passed with zero failures, including immediate upload/download resume and resume from the download progress callback: native XCTest results. These exercise the real GTMSessionFetcher callbacks with bounded waits and teardown gate release.