fix strings type hints and bugs

[0xRavenspar]

Implements the changes made in mandiant/capa#2555 to floss/strings.py.

Changes made:

• Added type hints
• fixed the strings.py helpers
• consolidated the tests into a single file
• Added extra test cases to check for usage

Please do let me know if the tests are alright and if i need to make any changes

Closes #1094

[gemini-code-assist]

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Summary of Changes

This pull request addresses improvements to the floss/strings.py file, focusing on enhancing code clarity, maintainability, and robustness. The changes include the addition of type hints, bug fixes in the helper functions, consolidation of tests into a single file (tests/test_strings.py), and the addition of new test cases to improve code coverage. The pull request description indicates that these changes are based on a related pull request in another repository.

Highlights

• Type Hinting: Added type hints to functions in floss/strings.py to improve code readability and maintainability.
• Bug Fixes: Corrected issues within the helper functions in floss/strings.py, specifically addressing the buf_filled_with function to ensure accurate checks for buffers filled with repeating characters.
• Test Consolidation and Expansion: Consolidated all tests into a single file (tests/test_strings.py) and added new test cases to cover various scenarios, including edge cases and mmap usage, enhancing the reliability of the floss/strings.py module.
• Input Validation: Added input validation to extract_ascii_strings and extract_unicode_strings to raise a ValueError if the minimum string length n is not a positive integer.

Changelog

Click here to see the changelog

• floss/strings.py
  • Added type hints to function signatures.
  • Improved the buf_filled_with function to correctly handle buffers of various sizes and edge cases, including empty buffers.
  • Added a check in buf_filled_with to raise a ValueError if the character value is outside the valid byte range (0-255).
  • Added input validation to extract_ascii_strings and extract_unicode_strings to ensure the minimum string length is positive.
  • Updated docstrings to use 'Params' instead of ':param' and ':type' for parameter descriptions.
  • Removed redundant return statements when the input buffer is empty.
• tests/test_buf_filled_with.py
  • Removed this file as tests were consolidated into tests/test_strings.py.
• tests/test_strings.py
  • Consolidated tests from tests/test_buf_filled_with.py into this file.
  • Added comprehensive test cases for buf_filled_with, including tests for single repeating bytes, mixed bytes, edge cases (empty buffer, single byte), large buffers, and mmap usage.
  • Added tests for extract_ascii_strings covering empty buffers, basic ASCII extraction, minimum length constraints, non-ASCII characters, buffers with only non-ASCII characters, and skipping repeated bytes.
  • Added tests for extract_unicode_strings covering basic UTF-16LE extraction, minimum length constraints, invalid UTF-16LE sequences, and skipping repeated bytes.

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[gemini-code-assist]

Code Review

The pull request addresses type hints and bug fixes in the floss/strings.py file, consolidates tests, and adds new test cases. The changes look good overall, with improvements in code clarity and test coverage.

Summary of Findings

• Input Validation: The buf_filled_with function validates the character input to ensure it's within the byte range (0-255). This is good for preventing unexpected behavior. The extract_ascii_strings and extract_unicode_strings functions validate that the minimum string length n is positive, raising a ValueError if it's not. This is important for preventing errors and ensuring the functions behave as expected.
• Test Coverage: The tests have been consolidated into a single file and expanded with additional test cases, which improves the overall test coverage and reliability of the strings.py module.
• Code Clarity: The addition of type hints enhances code readability and maintainability. The docstrings for the functions have been updated to provide clear explanations of the arguments and return values.

Merge Readiness

The pull request is in good shape and addresses the issues outlined in the original issue. The code is more robust with the added input validation and has improved test coverage. I am unable to directly approve this pull request, and recommend that others review and approve this code before merging.

[williballenthin]

thanks @0xRavenspar!

[mr-tz]

Looks good besides one question.