fix: decode Uint8Array and multi-byte UTF-8 in API error messages

[kimjune01]

Summary

Fixes #19851

• _fixGaxiosErrorData() now handles Uint8Array/Buffer instances directly (not just comma-separated strings)
• Replaced String.fromCharCode() with TextDecoder for correct multi-byte UTF-8 decoding
• Added byte range validation (0-255) to avoid false positives on comma-separated strings that aren't byte values

Test plan

• Existing tests pass (32/32)
• New test: Uint8Array data is decoded to string
• New test: multi-byte UTF-8 comma-separated bytes (e.g. "72,195,169,108,108,111" → "Héllo")
• New test: values outside 0-255 are left unchanged
• Existing test: non-numeric comma strings are left unchanged

[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 enhances the error handling mechanism by improving the decoding of API error messages originating from Gaxios. It addresses issues where error response data might be returned as raw byte arrays or comma-separated byte strings, ensuring that these messages are correctly interpreted and displayed as human-readable UTF-8 strings, thereby improving the clarity and utility of error logging.

Highlights

• Direct Uint8Array Handling: The _fixGaxiosErrorData() function now directly processes Uint8Array and Buffer instances, ensuring proper decoding of raw byte data from Gaxios errors.
• Multi-byte UTF-8 Decoding: Replaced String.fromCharCode() with TextDecoder to correctly handle multi-byte UTF-8 characters when decoding comma-separated byte strings.
• Byte Range Validation: Implemented validation to ensure that comma-separated strings are only treated as byte arrays if all values are within the 0-255 range, preventing incorrect decoding of non-byte strings.

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[gemini-code-assist]

Code Review

This pull request effectively addresses a bug in how Gaxios error messages are decoded. The implementation correctly handles Uint8Array and multi-byte UTF-8 strings by using TextDecoder, which is a significant improvement over the previous String.fromCharCode() approach. The addition of byte-range validation for comma-separated strings adds robustness. The new tests are comprehensive and validate the fix. The changes are well-implemented and I have no further recommendations.

[cocosheng-g]

/gemini review

[gemini-code-assist]

Code Review

This pull request updates the _fixGaxiosErrorData method in loggingContentGenerator.ts to correctly decode Gaxios error responses that may arrive as Uint8Array or comma-separated byte strings, ensuring proper UTF-8 handling. Corresponding unit tests have been added to loggingContentGenerator.test.ts to verify these decoding scenarios and handle invalid byte ranges. I have no feedback to provide as there are no review comments.