in_forward: fix stale byte accounting when multiple frames share a buffer

[zshuang0316]

Summary

In fw_prot_process, the inner frame loop tracks how many bytes each decoded object consumed in all_used, then uses it to trim conn->buf once the buffer is drained. The first object is parsed with msgpack_unpacker_next_with_size(unp, &result, &bytes), but the loop tail advanced to the next object with the plain msgpack_unpacker_next(unp, &result), which does not refresh bytes.

When several frames arrive in a single buffer — common with compressed payloads, which are small — every iteration after the first adds the previous object's stale bytes to all_used. The resulting total is wrong, so conn->buf is trimmed by the wrong offset and the remaining frames in the buffer desync.

The fix uses msgpack_unpacker_next_with_size() at the loop tail as well, so bytes is refreshed for every object, matching the initial parse.

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Backporting

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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 message parsing so incoming data is counted more accurately during processing.
  • Helped ensure multi-packet or multi-object streams are handled reliably without affecting byte tracking.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: b3577383-8ef4-4aa1-85ab-54aeaf0c8171

📥 Commits

Reviewing files that changed from the base of the PR and between a1e05fc and caa1918.

📒 Files selected for processing (1)

• plugins/in_forward/fw_prot.c

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📝 Walkthrough

Walkthrough

A single-line fix in the forward input plugin's msgpack parsing loop switches from msgpack_unpacker_next to msgpack_unpacker_next_with_size, ensuring the decoded object size populates the bytes variable used for byte accounting.

Changes

Msgpack Unpacking Fix

Layer / File(s)	Summary
Switch to size-returning unpacker call plugins/in_forward/fw_prot.c	Replaces the msgpack unpacking call with a variant that returns the object size, fixing the bytes/all_used accounting in the parsing loop.

Estimated code review effort: 1 (Trivial) | ~3 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main fix in in_forward: stale byte accounting for shared-buffer frames.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
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.

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[zshuang0316]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Already looking forward to the next diff.

Reviewed commit: caa1918b6c

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