Fix BadZipFile error

[belluzj]

Hello Simon, this is a reproducer for the issue here: googlefonts/diffenator2#97

It's a race condition when two process/instances of fontbakery/diffenator2 try to call youseedee at the same, there's a race for downloading and opening the ZIP.

The problem is on this line: https://github.com/simoncozens/youseedee/blob/master/lib/youseedee/__init__.py#L31, one thread will see the half-downloaded ZIP from the other and try to open it.

Possible mitigation would be to write a lock file next to the ZIP, that stays here until the download is finished. The process would be:

1. Check if ZIP present
2. Check if lock file present
   a) if yes, wait for it to go away
   b) if not, create it and download
3. Open the ZIP

I can add that code on Monday if you'd like.

$ pytest
=================================================================================== test session starts ===================================================================================
platform win32 -- Python 3.8.10, pytest-7.4.3, pluggy-1.3.0
rootdir: C:\UsersLocal\jany.belluz\Documents\code\youseedee
collected 1 item

tests\test_concurrent_download.py F                                                                                                                                                  [100%]

======================================================================================== FAILURES =========================================================================================
________________________________________________________________________________ test_concurrent_download _________________________________________________________________________________

tmp_path = WindowsPath('C:/Users/jany.belluz/AppData/Local/Temp/pytest-of-jany.belluz/pytest-749/test_concurrent_download0')

    def test_concurrent_download(tmp_path):
        """Download the ZIP twice at the same time and make sure it doesn't crash.
        """
        # Fake user home dir (where youseedee writes its files)
        os.environ['HOME'] = str(tmp_path)
        os.environ['USERPROFILE'] = str(tmp_path)

        with ThreadPoolExecutor(max_workers=2) as executor:
            future_1 = executor.submit(ucd_data, ord('a'))
            sleep(0.1)
            future_2 = executor.submit(ucd_data, ord('a'))
>           assert future_1.result() == future_2.result()

tests\test_concurrent_download.py:20:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
C:\Program Files\Python38\lib\concurrent\futures\_base.py:437: in result
    return self.__get_result()
C:\Program Files\Python38\lib\concurrent\futures\_base.py:389: in __get_result
    raise self._exception
C:\Program Files\Python38\lib\concurrent\futures\thread.py:57: in run
    result = self.fn(*self.args, **self.kwargs)
lib\youseedee\__init__.py:186: in ucd_data
    out.update(props["datareader"](file, codepoint))
lib\youseedee\__init__.py:82: in dictget
    fileentry["data"] = fileentry["reader"](filename)
lib\youseedee\__init__.py:67: in parse_file_semicolonsep
    ensure_files()
lib\youseedee\__init__.py:49: in ensure_files
    with zipfile.ZipFile(zip_path, 'r') as zip_ref:
C:\Program Files\Python38\lib\zipfile.py:1269: in __init__
    self._RealGetContents()
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <zipfile.ZipFile [closed]>

    def _RealGetContents(self):
        """Read in the table of contents for the ZIP file."""
        fp = self.fp
        try:
            endrec = _EndRecData(fp)
        except OSError:
            raise BadZipFile("File is not a zip file")
        if not endrec:
>           raise BadZipFile("File is not a zip file")
E           zipfile.BadZipFile: File is not a zip file

C:\Program Files\Python38\lib\zipfile.py:1336: BadZipFile
---------------------------------------------------------------------------------- Captured stdout call -----------------------------------------------------------------------------------
Downloading Unicode Character Database...
[==================================================]
================================================================================= short test summary info =================================================================================
FAILED tests/test_concurrent_download.py::test_concurrent_download - zipfile.BadZipFile: File is not a zip file
==================================================================================== 1 failed in 3.51s ====================================================================================

[belluzj]

I added a fix with a lock file for the ZIP, using this package seemingly from the Tox team: https://pypi.org/project/filelock/

[simoncozens]

Thanks so much for this!