fix: Default "platform" field in zip files should be set to the local platform, rather than always "Unix" (#470)

[roynor]

Fixed the issue where the compression platform was set to Unix in the Windows environment. Now the platform can be automatically set to Dos or Unix based on the specific operating system.

[gemini-code-assist]

Summary of Changes

Hello @roynor, 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 resolves a bug where the platform field in generated zip files was incorrectly set to "Unix" even when created on a Windows operating system. The change introduces automatic detection of the operating system during zip file creation, ensuring that the system field is accurately set to "Dos" for Windows environments and "Unix" for Linux environments, improving compatibility and correctness of zip archives.

Highlights

• Platform Auto-detection: The ZipFileData structure now automatically detects the operating system (Windows, Linux) to set the appropriate compression platform (Dos, Unix) for zip files.
• Bug Fix: Addresses an issue where zip files created on Windows incorrectly reported their platform as Unix, ensuring correct platform identification.

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[gemini-code-assist]

Code Review

This pull request correctly addresses the issue of the zip platform being hardcoded to Unix by introducing OS detection. The platform is now correctly set to DOS on Windows. However, the check for Unix-like systems is too specific, using cfg!(linux), which will incorrectly classify other common platforms like macOS as System::Unknown. I've provided a suggestion to use the more general cfg!(unix) to properly support all Unix-like systems.

[pzhlkj6612]

Simplify:

Suggested change

	system: system,
	system,

[pzhlkj6612]

failures:
    read::test::test_cannot_symlink_outside_destination
    write::test::write_mimetype_zip
    write::test::write_non_utf8
    write::test::write_symlink_simple
    write::test::write_symlink_wonky_paths
    write::test::write_zip_dir

test result: FAILED. 82 passed; 6 failed

Well, I have no idea why all test suites in the "tests" directory was not be counted without specifying --lib ¹. For now, I encountered failed tests in the test suite "end_to_end" on Windows and I think I know the reason.

In initialize_local_block(), we have no parameter to designate if the current ZipFileData is related to a directory or a file, So the external_attributes field is always permissions << 16 ².

Because of the incorrect external_attributes, the System::Dos branch in unix_mode() always produces ffi::S_IFREG | 0o0664 == 0o0100664 ³. This incorrect Unix mode has at least two negative effects on our ZIP file:

• It may cause an incorrect version_made_by field by making the check mode & S_IFDIR == S_IFDIR in version_needed() always fail ⁴.
• It does cover the real Unix mode of every item by a constant 0o664 ⁵ when someone calls the unix_mode() function.

The 2nd point is the reason why the "end_to_end" suite failed.

Footnotes

1. https://github.com/zip-rs/zip2/actions/runs/19553408314/job/55990236771?pr=471 ↩

2. /src/types.rs#L750 ↩

3. /src/types.rs#L626-L638 ↩

4. /src/types.rs#L669-L677 ↩

5. /tests/end_to_end.rs#L252 ↩