fix truncate size can be None

[claudius-kienle]

If I execute a script that contains following code with gunicorn and eventlet, I get the exception that

File "/usr/local/lib/python3.8/site-packages/eventlet/greenio/py3.py", line 165, in truncate
--
Sun, Feb 12 2023 8:54:19 pm | rv = _original_os.ftruncate(self._fileno, size)
Sun, Feb 12 2023 8:54:19 pm | TypeError: an integer is required (got type NoneType)

with os.fdopen(os.open(path, os.O_WRONLY | os.O_CREAT, 0o600), 'w') as file:
            file.seek(0)
            file.write(json.dumps(token_data, indent=2))
            file.truncate()

Consequently, I assumed that truncate() must also work if size=None.
This pull request checks if size is None and in this case replaces it with -1.

[temoto]

Consequently, I assumed that truncate() must also work if size=None.

Why?

[temoto]

never mind, it's "because CPython does so" https://github.com/python/cpython/blob/main/Modules/_io/bufferedio.c#L1287

thanks for patch

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (8f5ebf1) 55% compared to head (94e748e) 55%.

Files	Patch %	Lines
eventlet/greenio/py3.py	0%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##           master   #789   +/-   ##
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- Coverage      55%    55%   -1%     
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  Files          90     90           
  Lines        9878   9880    +2     
  Branches     1831   1832    +1     
=====================================
  Hits         5460   5460           
- Misses       4044   4045    +1     
- Partials      374    375    +1     

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py39asyncio	50% <0%> (-1%)	⬇️
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