out_flowcounter: Fix incorrect bytes calcuation

[cosmo0920]

---

Enter [N/A] in the box, if an item is not applicable to your change.

Testing
Before we can approve your change; please submit the following in a comment:

• Example configuration file for the change
• Debug log output from testing the change

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

If this is a change to packaging of containers or native binaries then please confirm it works for all targets.

• Run local packaging test showing all targets (including any new ones) build.
• Set ok-package-test label to test for all targets (requires maintainer to do).

Documentation

• Documentation required for this feature

Backporting

• Backport to latest stable release.

---

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
  • Corrected per-event byte accounting so byte consumption reflects actual bytes processed for each event, including when records are skipped or invalid. This resolves cases where byte counts were previously reported as zero.

_{✏️ Tip: You can customize this high-level summary in your review settings.}

[coderabbitai]

Walkthrough

The out_flowcounter plugin records per-event byte consumption by reading log_decoder.offset into off, computing byte_data = off - last_off, and updating last_off for both processed and skipped/invalid-time records to maintain correct byte accounting.

Changes

Cohort / File(s)	Summary
Byte offset tracking plugins/out_flowcounter/out_flowcounter.c	Read log_decoder.offset into off, compute per-event byte_data as off - last_off, update last_off after processed events and in skip/invalid-time paths to preserve correct offset state

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

• Verify last_off initialization and updates cover all code paths (processed, skipped, invalid-time).
• Confirm byte_data calculation handles edge cases (e.g., zero/negative deltas) as intended.

Poem

🐰 I hop through logs with careful flight,
I mark each offset, small and light,
Subtract the last to find byte song,
For every event I carry along,
Counting flow until the night is bright,
A rabbit’s tally — neat and right. 🥕

Pre-merge checks and finishing touches

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	You can run @coderabbitai generate docstrings to improve docstring coverage.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change—fixing incorrect byte calculation in the out_flowcounter plugin.

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch cosmo0920-fix-incorrect-bytes-on-flowcounter

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[coderabbitai]

Actionable comments posted: 1

📜 Review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between c88c545 and 8c20375.

📒 Files selected for processing (1)

• plugins/out_flowcounter/out_flowcounter.c (1 hunks)

⏰ Context from checks skipped due to timeout of 90000ms. You can increase the timeout in your CodeRabbit configuration to a maximum of 15 minutes (900000ms). (31)

• GitHub Check: pr-windows-build / call-build-windows-package (Windows 32bit, x86, x86-windows-static, 3.31.6)
• GitHub Check: pr-windows-build / call-build-windows-package (Windows 64bit, x64, x64-windows-static, 3.31.6)
• GitHub Check: pr-windows-build / call-build-windows-package (Windows 64bit (Arm64), amd64_arm64, -DCMAKE_SYSTEM_NAME=Windows -DCMA...
• GitHub Check: run-ubuntu-unit-tests (-DSANITIZE_UNDEFINED=On, 3.31.6, gcc, g++)
• GitHub Check: PR - fuzzing test
• GitHub Check: run-ubuntu-unit-tests (-DFLB_SANITIZE_THREAD=On, 3.31.6, clang, clang++)
• GitHub Check: run-ubuntu-unit-tests (-DFLB_SANITIZE_MEMORY=On, 3.31.6, gcc, g++)
• GitHub Check: run-ubuntu-unit-tests (-DFLB_ARROW=On, 3.31.6, gcc, g++)
• GitHub Check: run-ubuntu-unit-tests (-DFLB_SIMD=Off, 3.31.6, clang, clang++)
• GitHub Check: run-ubuntu-unit-tests (-DFLB_COMPILER_STRICT_POINTER_TYPES=On, 3.31.6, gcc, g++)
• GitHub Check: run-ubuntu-unit-tests (-DFLB_SIMD=Off, 3.31.6, gcc, g++)
• GitHub Check: run-ubuntu-unit-tests (-DSANITIZE_ADDRESS=On, 3.31.6, gcc, g++)
• GitHub Check: run-ubuntu-unit-tests (-DFLB_SANITIZE_MEMORY=On, 3.31.6, clang, clang++)
• GitHub Check: run-ubuntu-unit-tests (-DFLB_COVERAGE=On, 3.31.6, gcc, g++)
• GitHub Check: run-ubuntu-unit-tests (-DFLB_SIMD=On, 3.31.6, clang, clang++)
• GitHub Check: run-ubuntu-unit-tests (-DFLB_SIMD=On, 3.31.6, gcc, g++)
• GitHub Check: run-ubuntu-unit-tests (-DFLB_SANITIZE_THREAD=On, 3.31.6, gcc, g++)
• GitHub Check: run-ubuntu-unit-tests (-DSANITIZE_UNDEFINED=On, 3.31.6, clang, clang++)
• GitHub Check: run-ubuntu-unit-tests (-DFLB_SMALL=On, 3.31.6, gcc, g++)
• GitHub Check: pr-compile-without-cxx (3.31.6)
• GitHub Check: run-ubuntu-unit-tests (-DSANITIZE_ADDRESS=On, 3.31.6, clang, clang++)
• GitHub Check: run-ubuntu-unit-tests (-DFLB_SMALL=On, 3.31.6, clang, clang++)
• GitHub Check: run-ubuntu-unit-tests (-DFLB_JEMALLOC=Off, 3.31.6, clang, clang++)
• GitHub Check: pr-compile-system-libs (-DFLB_PREFER_SYSTEM_LIBS=On, 3.31.6, clang, clang++, ubuntu-24.04, clang-14)
• GitHub Check: pr-compile-system-libs (-DFLB_PREFER_SYSTEM_LIBS=On, 3.31.6, gcc, g++, ubuntu-22.04, clang-12)
• GitHub Check: run-ubuntu-unit-tests (-DFLB_JEMALLOC=On, 3.31.6, gcc, g++)
• GitHub Check: pr-compile-system-libs (-DFLB_PREFER_SYSTEM_LIBS=On, 3.31.6, gcc, g++, ubuntu-24.04, clang-14)
• GitHub Check: pr-compile-system-libs (-DFLB_PREFER_SYSTEM_LIBS=On, 3.31.6, clang, clang++, ubuntu-22.04, clang-12)
• GitHub Check: run-ubuntu-unit-tests (-DFLB_JEMALLOC=Off, 3.31.6, gcc, g++)
• GitHub Check: pr-compile-centos-7
• GitHub Check: run-ubuntu-unit-tests (-DFLB_JEMALLOC=On, 3.31.6, clang, clang++)

🔇 Additional comments (1)

plugins/out_flowcounter/out_flowcounter.c (1)

194-194: The types are correctly chosen for their semantic purposes and should not be changed. The variable off is size_t because it directly mirrors log_decoder.offset (which is defined as size_t in the struct), while last_off and byte_data are uint64_t for accumulated byte count tracking. The explicit cast at line 234 properly documents the necessary type conversion during the subtraction. Changing off to uint64_t would break the correspondence between the variable and its source field.

Likely an incorrect or invalid review comment.

[coderabbitai]

Actionable comments posted: 0

🧹 Nitpick comments (1)

plugins/out_flowcounter/out_flowcounter.c (1)

194-194: Consider using uint64_t for off to match last_off and byte_data.

While the current implementation correctly handles the type difference between off (size_t) and last_off (uint64_t) through explicit casting at line 235, declaring off as uint64_t would improve type consistency and clarity.

Apply this diff to align types:

-    size_t off = 0;
+    uint64_t off = 0;

📜 Review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 8c20375 and d19af5f.

📒 Files selected for processing (1)

• plugins/out_flowcounter/out_flowcounter.c (2 hunks)

🧰 Additional context used

🧠 Learnings (1)

📚 Learning: 2025-10-23T07:43:16.216Z

Learnt from: cosmo0920
Repo: fluent/fluent-bit PR: 11059
File: plugins/in_tail/tail_file.c:1618-1640
Timestamp: 2025-10-23T07:43:16.216Z
Learning: In plugins/in_tail/tail_file.c, when truncate_long_lines is enabled and the buffer is full, the early truncation path uses `lines > 0` as the validation pattern to confirm whether process_content successfully processed content. This is intentional to track occurrences of line processing rather than byte consumption, and consuming bytes based on `processed_bytes > 0` would be overkill for this validation purpose.

Applied to files:

• plugins/out_flowcounter/out_flowcounter.c

⏰ Context from checks skipped due to timeout of 90000ms. You can increase the timeout in your CodeRabbit configuration to a maximum of 15 minutes (900000ms). (26)

• GitHub Check: pr-windows-build / call-build-windows-package (Windows 64bit, x64, x64-windows-static, 3.31.6)
• GitHub Check: pr-windows-build / call-build-windows-package (Windows 64bit (Arm64), amd64_arm64, -DCMAKE_SYSTEM_NAME=Windows -DCMA...
• GitHub Check: pr-windows-build / call-build-windows-package (Windows 32bit, x86, x86-windows-static, 3.31.6)
• GitHub Check: run-ubuntu-unit-tests (-DFLB_SANITIZE_THREAD=On, 3.31.6, clang, clang++)
• GitHub Check: run-ubuntu-unit-tests (-DFLB_ARROW=On, 3.31.6, gcc, g++)
• GitHub Check: PR - fuzzing test
• GitHub Check: run-ubuntu-unit-tests (-DFLB_SIMD=On, 3.31.6, gcc, g++)
• GitHub Check: run-ubuntu-unit-tests (-DFLB_SANITIZE_MEMORY=On, 3.31.6, gcc, g++)
• GitHub Check: run-ubuntu-unit-tests (-DFLB_SIMD=Off, 3.31.6, clang, clang++)
• GitHub Check: run-ubuntu-unit-tests (-DFLB_COMPILER_STRICT_POINTER_TYPES=On, 3.31.6, gcc, g++)
• GitHub Check: run-ubuntu-unit-tests (-DFLB_SIMD=On, 3.31.6, clang, clang++)
• GitHub Check: run-ubuntu-unit-tests (-DFLB_SANITIZE_MEMORY=On, 3.31.6, clang, clang++)
• GitHub Check: run-ubuntu-unit-tests (-DFLB_SANITIZE_THREAD=On, 3.31.6, gcc, g++)
• GitHub Check: run-ubuntu-unit-tests (-DFLB_SIMD=Off, 3.31.6, gcc, g++)
• GitHub Check: run-ubuntu-unit-tests (-DFLB_COVERAGE=On, 3.31.6, gcc, g++)
• GitHub Check: run-ubuntu-unit-tests (-DSANITIZE_UNDEFINED=On, 3.31.6, clang, clang++)
• GitHub Check: run-ubuntu-unit-tests (-DFLB_JEMALLOC=Off, 3.31.6, gcc, g++)
• GitHub Check: run-ubuntu-unit-tests (-DFLB_SMALL=On, 3.31.6, gcc, g++)
• GitHub Check: run-ubuntu-unit-tests (-DFLB_JEMALLOC=Off, 3.31.6, clang, clang++)
• GitHub Check: run-ubuntu-unit-tests (-DFLB_JEMALLOC=On, 3.31.6, gcc, g++)
• GitHub Check: run-ubuntu-unit-tests (-DSANITIZE_ADDRESS=On, 3.31.6, clang, clang++)
• GitHub Check: run-ubuntu-unit-tests (-DSANITIZE_UNDEFINED=On, 3.31.6, gcc, g++)
• GitHub Check: run-ubuntu-unit-tests (-DSANITIZE_ADDRESS=On, 3.31.6, gcc, g++)
• GitHub Check: run-ubuntu-unit-tests (-DFLB_SMALL=On, 3.31.6, clang, clang++)
• GitHub Check: run-ubuntu-unit-tests (-DFLB_JEMALLOC=On, 3.31.6, clang, clang++)
• GitHub Check: pr-compile-centos-7

🔇 Additional comments (3)

plugins/out_flowcounter/out_flowcounter.c (3)

219-220: LGTM! Offset capture enables per-event byte tracking.

Capturing log_decoder.offset after each successful decode correctly records the stream position for per-event byte accounting.

---

231-231: LGTM! Skipped record byte accounting is now correct.

Updating last_off before skipping ensures that the skipped record's byte range is not incorrectly attributed to the next valid record. This resolves the issue flagged in the previous review.

---

235-236: LGTM! Byte accounting logic is correct.

The delta calculation (byte_data = off - last_off) accurately measures bytes consumed by the current event, and updating last_off properly maintains state for the next iteration.