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refactor: string encoding to use utf8cpp and add tests (#1443 )

Update string encoding implementation to use utf8cpp

This change updates the string encoding implementation to use the utf8cpp library for improved robustness and consistency across platforms. It refactors the encoding functions in src/framework/stdext/string.cpp, adds comprehensive unit tests, updates build configurations to include utf8cpp, and documents the new encoding policy and behavior.

String encoding improvements

Refactored all string encoding functions in src/framework/stdext/string.cpp to use the utf8cpp library, providing strict UTF-8 validation, robust conversions between UTF-8, Latin-1, and UTF-16, and consistent error handling.

Added a new documentation file docs/string-encoding-policy.md detailing the updated encoding policy, error handling, dependencies, and testing strategy.

Testing enhancements

Added a new unit test suite in tests/stdext/string_encoding_test.cpp covering UTF-8 validation, conversions, roundtrip consistency, control character handling, and platform-specific UTF-16 conversions.

Updated the test build configuration to include the new test directory and sources.

Build system updates

Updated src/CMakeLists.txt to require and link the utf8cpp library for all platforms, ensuring proper integration.

Added utf8cpp as a dependency in vcpkg.json for package management.

2025-11-20 02:08:02 -03:00

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String Encoding Policy

Overview

The string encoding functions in src/framework/stdext/string.cpp have been updated to use the utf8cpp library for robust and consistent encoding handling across all platforms.

Invalid Data Policy

UTF-8 Validation (`is_valid_utf8`)

Returns true only if the entire input is valid UTF-8
Invalid sequences return false
Uses strict UTF-8 validation rules

UTF-8 to Latin-1 Conversion (`utf8_to_latin1`)

Maps representable code points (0x00-0xFF) to Latin-1
Skips unrepresentable code points (> 0xFF)
Filters out control characters except tab (0x09), CR (0x0D), and LF (0x0A)
On invalid UTF-8 input, returns an empty string

Latin-1 to UTF-8 Conversion (`latin1_to_utf8`)

Converts all Latin-1 bytes (0x00-0xFF) to UTF-8
Always produces valid UTF-8 output
On encoding error (should not occur), returns an empty string

UTF-16 Conversions (Windows only)

utf8_to_utf16: Converts valid UTF-8 to UTF-16
utf16_to_utf8: Converts valid UTF-16 to UTF-8
latin1_to_utf16: Converts via UTF-8 intermediate
utf16_to_latin1: Converts via UTF-8 intermediate
All functions return empty string on invalid input

Dependency

The implementation uses utf8cpp (also known as UTF8-CPP), a lightweight header-only library:

Zero transitive dependencies
Minimal binary size impact
Cross-platform compatibility
Well-tested and widely used

Performance

The new implementation maintains performance within 5% of the original manual implementation while providing:

Correct handling of all UTF-8 edge cases
Proper validation of overlong sequences
Rejection of invalid surrogate pairs
Consistent behavior across all platforms

Testing

Unit tests in test_string_encoding.cpp cover:

Valid and invalid UTF-8 sequences
Boundary cases and edge conditions
Roundtrip conversions
Control character handling
Platform-specific UTF-16 conversions

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