log_event_encoder: add direct-emit path for FLUENT_BIT_V2 format

[edsiper]

For FLUENT_BIT_V2 log format, emit_record can append the record as raw msgpack array bytes [ [timestamp, metadata], body ] directly to the main buffer instead of building it in the root buffer and then copying it. This avoids root buffer construction and one full-record copy per committed log record.

The record is emitted without a msgpack string wrapper so the on-wire format matches the existing path and decoders that expect a root array continue to work.

Estimated gain is on the order of 1–3% in the encoder hot path per record;

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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

• Performance
  • Improved log encoding for Fluent Bit v2 with a new direct-emit fast path that reduces intermediate buffering, yielding faster record processing and lower CPU/memory overhead while preserving the previous behavior as a fallback.

[coderabbitai]

📝 Walkthrough

Walkthrough

Adds a direct-emit fast path in the log event encoder that, for FLUENT_BIT_V2 with metadata and body present, serializes and appends a compact MessagePack sequence [timestamp, metadata, body] directly into the main buffer; preserves the original root-buffer-based emission as a fallback.

Changes

Cohort / File(s)

Summary

Log Event Encoder Optimization src/flb_log_event_encoder.c

Introduces a FLUENT_BIT_V2 fast path in flb_log_event_encoder_emit_record that builds a small MsgPack sequence and writes it directly to the main buffer when timestamp, metadata, and body are present. Adds flb_byteswap.h and string.h includes, constructs fixed MsgPack header and network-order timestamp, handles serialization success/failure, and retains the previous root-buffer emission as fallback. Key areas: byte-order handling, direct buffer writes, MsgPack header construction, and conditional control-flow changes for the newer path.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~22 minutes

Poem

🐰 I nibble bytes and swap with care,

I pack the time, meta, body fair,
A shortcut leap into the main,
No extra copies—what a gain! ✨

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 66.67% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ 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 'log_event_encoder: add direct-emit path for FLUENT_BIT_V2 format' accurately and specifically describes the main change: adding a direct-emit optimization path for the FLUENT_BIT_V2 format in the log event encoder.

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✨ 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 log-event-encoder-perf-improvement

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[chatgpt-codex-connector]

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