lua: bound MessagePack reads when pushing values to Lua

[edsiper]

Problem

flb_lua_pushmpack() pushes a MessagePack value read with mpack onto the Lua
stack. For strings, binaries and extensions it advanced reader->data by the
declared length without checking it against the remaining data, and it
ignored reader errors. A truncated value read past the end of the buffer.
Nesting had no limit, and nested tables were created without growing the Lua
stack.

Change

• Read the bytes with mpack_read_bytes_inplace(), which checks the length,
  and fail on any reader error.
• Limit nesting to 512 levels, the same limit used for JSON packing.
• Grow the Lua stack for every nested table.
• On failure return -1 and leave the Lua stack as it was.

Valid input decodes as before. The function keeps its signature.

Testing

New lua_pushmpack_invalid case in tests/internal/lua.c:

• a truncated string;
• an array missing elements;
• a truncated binary inside a map;
• 512 and 513 levels of nesting;
• a valid value after the rejected ones.

It fails on master and passes with this change.

ctest --test-dir build -R lua                          # 2/2 passed
valgrind --leak-check=full build/bin/flb-it-lua         # clean
pytest scenarios/filter_lua                             # 9 passed
VALGRIND=1 VALGRIND_STRICT=1 pytest scenarios/filter_lua  # 9 passed, no errors

Summary by CodeRabbit

• Bug Fixes
  • Invalid or incomplete MessagePack data now fails cleanly without leaving partial decoded data behind.
  • Deeply nested input is handled with a safety limit, while valid data within that limit continues to decode successfully.
  • Decoding remains usable after an invalid input is rejected.

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-17T20:39:19.948801Z	2c64e63	PR opened

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📥 Commits

Reviewing files that changed from the base of the PR and between f5374f7 and 2c64e63.

📒 Files selected for processing: 2

• src/flb_lua.c
• tests/internal/lua.c

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📝 Walkthrough

MessagePack decoding into Lua now uses a recursive helper with a 512-level nesting limit. It checks reader and Lua stack errors, propagates failures, and restores the original Lua stack state when decoding fails. Tests cover truncated inputs and the nesting boundary.

Changes: MessagePack-to-Lua Decoding

Layer / File(s)	Summary
Recursive decoding and failure handling src/flb_lua.c	A recursive helper decodes values with a 512-level depth limit. The decoder checks reader errors and Lua stack capacity. The public wrapper restores the original Lua stack top if decoding fails.
Decoder failure and depth tests tests/internal/lua.c	Tests cover truncated inputs, the 512- and 513-level nesting cases, unchanged stack state after failures, and valid decoding after a failure.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~15 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to 2c64e

No merge-blocking issue was identified. The decoder’s failure handling and depth limit are covered by the new tests.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 42.86% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 7 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly and concisely describes the main change: adding bounds to MessagePack reads when pushing values into Lua.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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