Fix mask_secret panic on multi-byte UTF-8 secrets

[alysajad]

Summary

Fixes a runtime panic in mask_secret() when a credential string contains multi-byte UTF-8 characters (accented letters, emoji, CJK, etc.) near the masking boundary. Discovered during a security audit (finding M-02).

Root Cause

The original code used byte-level slicing (&s[..4], &s[s.len()-4..]) on Rust &str. Rust strings are UTF-8, where a single character can be 1-4 bytes. If byte offset 4 lands inside a multi-byte character, Rust panics.

Fix

3-line change in the function body:

• s.len() -> s.chars().count() (count characters, not bytes)
• • &s[..4] -> s.chars().take(4).collect() (first 4 characters)
• • &s[s.len()-4..] -> s.chars().skip(n-4).collect() (last 4 characters)

Tests

Added mask_secret_multibyte_utf8 test covering accented Latin, Greek alphabet, and short multi-byte strings. All 64 tests in auth_commands pass with zero regressions.

Impact

• No breaking changes - output is identical for ASCII inputs
• • No performance impact - called at most twice per export on short strings
• • Single function, single file, single caller (handle_export)

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[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a critical runtime panic in the mask_secret function, which previously occurred when processing secrets containing multi-byte UTF-8 characters. The fix involves transitioning from byte-level string manipulation to character-based operations, ensuring robust handling of diverse character sets without panicking. This change maintains existing functionality for ASCII inputs, introduces no performance overhead, and is thoroughly validated with new tests.

Highlights

• Fixed mask_secret panic: Resolved a runtime panic in mask_secret() when handling multi-byte UTF-8 characters near masking boundaries, identified during a security audit (M-02).
• Root Cause Identified: The panic was caused by using byte-level slicing (&s[..4], &s[s.len()-4..]) on Rust &str, which can panic if a slice boundary falls within a multi-byte UTF-8 character.
• Implemented Character-Based Slicing: The mask_secret function was updated to use character-based counting (s.chars().count()) and slicing (s.chars().take(4).collect(), s.chars().skip(n-4).collect()) to correctly handle multi-byte UTF-8 characters.
• Added Comprehensive Tests: A new test, mask_secret_multibyte_utf8, was added to cover accented Latin, Greek alphabet, and short multi-byte strings, ensuring no regressions and full UTF-8 compatibility.

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[gemini-code-assist]

Code Review

This pull request addresses a potential panic in the mask_secret function when handling secrets with multi-byte UTF-8 characters. The fix correctly replaces byte-level string slicing with character-based iteration, which prevents panics on invalid character boundaries. The included tests for multi-byte strings effectively verify the fix and protect against future regressions. The changes are self-contained and address the described issue.

[googleworkspace-bot]

/gemini review

[gemini-code-assist]

Code Review

This pull request correctly fixes a panic in mask_secret for multi-byte UTF-8 strings and introduces other security enhancements like atomic file writes and symlink protection. My review includes two key suggestions: one to improve the performance of the new secret masking logic, and a critical fix to prevent blocking I/O in an async function, which could otherwise lead to performance issues.