[issue29468] zipfile should catch ValueError as well as OSError to detect bad seek calls

[Filipe Laíns]

Filipe Laíns  added the comment:

That would not stay true to its meaning. AFAIK there are no implied exceptions 
in file objects. Given the meaning of ValueError, I'd say it is appropriate 
here.

--
nosy: +FFY00

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[issue29468] zipfile should catch ValueError as well as OSError to detect bad seek calls

[Irit Katriel]

Irit Katriel  added the comment:

Maybe a better option is to change mmap's seek() to raise an OSError, because 
it's supposed to behave like a file object.

--
nosy: +iritkatriel
versions: +Python 3.11 -Python 3.6

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[issue29468] zipfile should catch ValueError as well as OSError to detect bad seek calls

[Joe Jevnik]

New submission from Joe Jevnik:

In zipfile.py only OSError is checked to see if seek fails:

```
def _EndRecData64(fpin, offset, endrec):
"""
Read the ZIP64 end-of-archive records and use that to update endrec
"""
try:
fpin.seek(offset - sizeEndCentDir64Locator, 2)
except OSError:
# If the seek fails, the file is not large enough to contain a ZIP64
# end-of-archive record, so just return the end record we were given.
return endrec
```

I belive that this should also catch ValueError so that other file-like objects 
may be passed to ZipFile. The particular case I ran into was passing an mmap 
object:

```
"""
$ python p.py
sys.version_info(major=3, minor=6, micro=0, releaselevel='final', serial=0)
[]
Traceback (most recent call last):
  File "p.py", line 34, in 
with mmap_shared_raw_zipfile(f.name) as zf:
  File "/usr/lib64/python3.6/contextlib.py", line 82, in __enter__
return next(self.gen)
  File "p.py", line 23, in mmap_shared_raw_zipfile
ZipFile(mm) as zf:
  File "/usr/lib64/python3.6/zipfile.py", line 1100, in __init__
self._RealGetContents()
  File "/usr/lib64/python3.6/zipfile.py", line 1163, in _RealGetContents
endrec = _EndRecData(fp)
  File "/usr/lib64/python3.6/zipfile.py", line 264, in _EndRecData
return _EndRecData64(fpin, -sizeEndCentDir, endrec)
  File "/usr/lib64/python3.6/zipfile.py", line 196, in _EndRecData64
fpin.seek(offset - sizeEndCentDir64Locator, 2)
ValueError: seek out of range
"""
from contextlib import contextmanager
import mmap
import sys
from tempfile import NamedTemporaryFile
from zipfile import ZipFile


print(sys.version_info)


@contextmanager
def mmap_shared_raw_zipfile(path):
"""Open a zipfile with mmap shared so the data can be shared in multiple
processes.

Parameters
--
path : str
The path the zipfile to open.

Notes
-
The context manager returns a :class:`zipfile.ZipFile` on enter.
"""
with open(path) as f, \
mmap.mmap(f.fileno(), 0, mmap.MAP_SHARED, mmap.PROT_READ) as mm, \
ZipFile(mm) as zf:
yield zf


with NamedTemporaryFile() as f:
ZipFile(f, mode='w').close()
print(ZipFile(f.name).infolist())


with NamedTemporaryFile() as f:
ZipFile(f, mode='w').close()
with mmap_shared_raw_zipfile(f.name) as zf:
print(zf.infolist())
```

--
components: Library (Lib)
messages: 287185
nosy: ll
priority: normal
severity: normal
status: open
title: zipfile should catch ValueError as well as OSError to detect bad seek 
calls
versions: Python 3.6

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