Fixed missing null terminator in config string used in Booster::save_buffer.

[metasim]

Use of an address sanitizer on Windows 11 detected a missing null terminator required when passing strings across the FFI boundary.

This fix wraps the config string in a Cstring, which ensures a null terminator.

Summary by CodeRabbit

• Bug Fixes
  • Fixed a critical issue in model buffer saving that improves memory safety and reliability. Proper string handling ensures configurations are correctly processed during model serialization, preventing potential crashes or data corruption.

[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: 26661e56-9621-4284-a529-7f138cabe7b1

📥 Commits

Reviewing files that changed from the base of the PR and between 2a357c2 and 56fe82a.

📒 Files selected for processing (1)

• src/booster.rs

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📝 Walkthrough

Walkthrough

In Booster::save_buffer, the JSON config string passed to the XGBoost FFI function XGBoosterSaveModelToBuffer is now wrapped in ffi::CString::new(...) to ensure NUL-termination, replacing the previous use of .as_bytes().as_ptr() on a non-NUL-terminated Rust String. CString construction errors are mapped to XGBError.

Changes

FFI Config String Fix

Layer / File(s)	Summary
NUL-terminated CString in save_buffer src/booster.rs	save_buffer now constructs a ffi::CString from the formatted JSON config string and passes config.as_ptr() to XGBoosterSaveModelToBuffer, replacing the previous config.as_bytes().as_ptr() call that lacked a NUL terminator. CString creation failure is explicitly handled via XGBError.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Poem

A rabbit once hopped through the FFI gate,
But the string it passed in had no null — oh fate!
Now wrapped in a CString, all tidy and right,
The pointer is safe as it marches to fight.
🐇 NUL-terminated, at last! What delight!

🚥 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 pull request title directly and accurately describes the primary change: fixing a missing null terminator in a config string in the Booster::save_buffer method, which aligns perfectly with the changeset and PR objectives.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
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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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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