out_s3: Clean up orphaned chunks

[cosmo0920]

Here is the consolidated summary:

• Empty queued chunks are deleted from both the upload queue and filesystem.
• Startup draining continues through restored chunks after failures when ordering is disabled. With preserve_data_ordering or $INDEX, it stops at the first failure to preserve object order.
• Empty historical stream directories are removed after draining.
• Timed-out chunks enter the ordered queue oldest-first instead of bypassing it through the periodic callback.
• Ordered retries run at their existing backoff deadline using a one-shot timer.
• CreateMultipartUpload and local multipart-creation failures count toward retry exhaustion, including with preserve_data_ordering false.
• Request-buffer construction failures are retried and eventually cleaned up instead of permanently locking the queue head.
• Retry-exhausted chunk files follow retry_exhausted_action.
• Multipart metadata is retained when chunk or completion retries are exhausted, preserving uploaded parts for restart recovery. It is removed only after successful completion or abort.
• Queue entries treat multipart upload references as non-owning and refresh them before each attempt, preventing dangling references when multiple chunks share an upload.
• Pending multipart completions continue while an ordered queue head is in backoff.
• Shutdown releases queued file locks before the final drain and avoids accessing an already-destroyed scheduler.
• ctx->retry_time remains in place with its existing accumulation and timeout behavior. It resets after a successful upload or terminal queue-head cleanup so stale delay does not affect subsequent chunks.
• Restored ChunkIO files loaded in the down state are temporarily brought up to obtain their logical content size and then returned to the down state.
• Restored down-chunk sizes are included in current_buffer_size or quarantine_buffer_size, preventing buffer usage from being under-reported after restart.
• No bundled ChunkIO code was modified.
• Added regressions for empty queue entries, multi-tag startup draining, $INDEX recovery ordering, ordered retry deadlines, timer-driven ordering, CreateMultipartUpload exhaustion, request-buffer construction failure, multipart recovery metadata, completion during backoff, shared multipart uploads, shutdown with a pending retry, and restored down-chunk accounting.
• The startup accounting regression creates CIO_MAX_CHUNKS_UP + 2 files, confirms at least two remain down with nonzero accounted sizes, and verifies that restored global usage exactly matches the live pre-restart total.

Verification:

• cmake --build build --target flb-rt-out_s3 -j8 — passed.
• ./build/bin/flb-rt-out_s3 startup_buffer_size_accounting — passed.
• ./build/bin/flb-rt-out_s3 — all 25 runtime cases passed.
• ctest --test-dir build -R '^flb-rt-out_s3$' --output-on-failure — passed.
• Full out_s3 integration scenario — 10 passed, 2 unsupported OTLP cases skipped.
• Focused retry-exhaustion integration coverage — passed.
• LEAKS=1 LEAKS_STRICT=1 tests/integration/.venv/bin/python -m pytest tests/integration/scenarios/out_s3/tests/test_out_s3_001.py -q — 10 passed, 2 expected skips; no strict Leaks failure.
• git diff HEAD --check — passed.
• Commit-prefix lint for the existing committed changes — passed.

A non-empty queued chunk can legitimately remain on disk while retry backoff is active. With preserve_data_ordering true, uploads remain intentionally serial; for retry_limit 5, each failed head chunk can incur 30 seconds of cumulative backoff plus request timeouts before terminal cleanup.
Accurate restoration of down ChunkIO file sizes remains separate work.

Also, @smiley-ci confirms that this PR is working well on his environment.

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Testing
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• Attached Valgrind output that shows no leaks or memory corruption was found

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Backporting

• Backport to latest stable release.

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Fluent Bit is licensed under Apache 2.0, by submitting this pull request I understand that this code will be released under the terms of that license.

Summary by CodeRabbit

• Bug Fixes
  • Improved S3 upload recovery while preserving chunk ordering and indexes after failures.
  • Added scheduled retries for timed-out uploads without allowing later chunks to bypass earlier ones.
  • Improved cleanup and recovery of failed, completed, aborted, and empty queued uploads.
  • Preserved recoverable multipart upload metadata after completion failures.
  • Improved recovery of buffered files across multiple input streams and buffer accounting.
  • Ensured pending uploads are released cleanly during shutdown.

[chatgpt-codex-connector]

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-02T11:20:40.958316Z	feda458	PR opened

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📝 Walkthrough

Walkthrough

S3 upload recovery now preserves $INDEX ordering after failures, schedules one-shot queue retries, deletes empty queued chunk files, and removes drained inactive streams during recovery. Runtime tests cover ordered retries, queue cleanup, multipart completion, and multi-stream recovery.

Changes

S3 upload recovery

Layer / File(s)	Summary
Recovery ordering and stream cleanup plugins/out_s3/s3.c, plugins/out_s3/s3_store.c	put_all_chunks records upload failures, stops ordered recovery when required, removes empty inactive streams during startup and flush recovery, and preserves streams during shutdown. Restored down chunks now provide their content size for buffer accounting.
Ordered upload queue and retry timers plugins/out_s3/s3.c, plugins/out_s3/s3.h, plugins/out_s3/s3_multipart.c	The queue selects the oldest timed-out chunk, schedules one-shot retries, processes pending multipart completions, removes invalid files, and releases queued entries during shutdown. Multipart removal remains file-local.
Upload failure accounting plugins/out_s3/s3.c	Upload creation and request-buffer failures now count toward chunk retry limits and use retryable queue handling.
Recovery, ordering, and cleanup validation tests/runtime/out_s3.c	Runtime tests validate retry deadlines, chunk order, completion during backoff, shared-upload retries, empty-file deletion, $INDEX recovery, buffer accounting, URI tracking, and drained stream removal.

Estimated code review effort: 4 (Complex) | ~60 minutes

Merge Risk: ⚪ Minimal · up to a4d13

This change improves S3 recovery buffer accounting for restored chunks while preserving their storage state. No merge-blocking correctness, data-integrity, or runtime risk remains.

Sequence Diagram(s)

sequenceDiagram
  participant cb_s3_upload
  participant s3_upload_queue
  participant Scheduler
  participant S3PutObject
  participant MultipartUpload
  cb_s3_upload->>s3_upload_queue: enqueue oldest timed-out chunk
  s3_upload_queue->>S3PutObject: upload queued chunk
  S3PutObject-->>s3_upload_queue: return success or retryable failure
  s3_upload_queue->>Scheduler: schedule one-shot retry
  Scheduler->>s3_upload_queue: retry at backoff deadline
  s3_upload_queue->>MultipartUpload: complete pending upload

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Suggested reviewers: edsiper

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 20.75% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 53 functions across 5 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly identifies the main change: cleaning up orphaned chunks in out_s3. It is concise and specific.

✨ Finishing Touches 💡 1

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• Commit unit tests in branch cosmo0920-further-mitigations-of-out_s3

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Reviewed commit: feda458399

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Actionable comments posted: 1

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Inline comments:
In `@plugins/out_s3/s3.c`:
- Around line 1778-1779: Update the recovery handling in s3_put_object at both
failure paths around result = -1 and continue so recovery stops when
key_fmt_has_seq_index is enabled, preventing a later chunk from reusing the
failed chunk’s index. Preserve existing recovery behavior when $INDEX is not
configured, and add coverage for two chunks with an injected first-chunk failure
to verify index ordering.

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