`zipfile` append corrupts a file due to auto filename sanitization

Bug report

Bug description:

When a ZIP archive is opened and rewritten in append mode, a member having a non-standard filename will be corrupted because its filename rewritten to the central directory is auto-sanitized and thus inconsistent with the immutable local file entry when loaded in the future.

This can easily happen if a member containing \ is added in POSIX and the archive is then appended in Windows.

For example:

import io
import zipfile
from unittest import mock

TESTFN = io.BytesIO()

# A file written in POSIX allows '\\'
with mock.patch('os.sep', '/'), mock.patch('os.altsep', None), \
     zipfile.ZipFile(TESTFN, mode="w") as zipfp:
    zi = zipfile.ZipInfo('MyFolder/My\\File.txt')
    zipfp.writestr(zi, 'foo')

# A file written in Windows has '\\' replaced with '/'
with mock.patch('os.sep', '\\'), mock.patch('os.altsep', '/'), \
     zipfile.ZipFile(TESTFN, "a") as zipfp:
    # trigger archive rewriting
    zipfp.comment = b''

with zipfile.ZipFile(TESTFN, "r") as zipfp:
    zi = zipfp.infolist()[0]
    print('content:', zipfp.read(zi))

The above code raises an error: zipfile.BadZipFile: File name in directory 'MyFolder/My/File.txt' and header b'MyFolder/My\\File.txt' differ.

CPython versions tested on:

3.16, 3.14

Operating systems tested on:

No response

Linked PRs

• gh-153626

まず issue の reproducer を実行し、Python の zipfile における append モードのアーカイブ書き換えとファイル名サニタイズのパスを調べてください。バックスラッシュを含む名前の member で作成したアーカイブに追記でき、その後、ディレクトリのファイル名とヘッダーのファイル名に不一致がない状態で読み取れるようになれば完了です。issue から PR gh-153626 にリンクされているので、まずその作業を確認してください。