[Patches] [ python-Patches-576327 ] zipfile when sizeof(long) == 8

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Patches item #576327, was opened at 2002-07-02 03:11
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Category: Library (Lib)
Group: Python 2.2.x
Status: Open
Resolution: None
Priority: 5
Submitted By: The Written Word (Albert Chin) (tww-china)
Assigned to: Nobody/Anonymous (nobody)
Summary: zipfile when sizeof(long) == 8

Initial Comment:
This bug also applies to Python 2.0.x and 2.1.x (most
likely every version).

When sizeof (long) == 8, like on Tru64 UNIX,
zipfile.testzip () fails due to a CRC error. The
problem is that in Lib/zipfile.py:
  crc = binascii.crc32(bytes)
converts the 32-bit binascii.crc32() return value to a
64-bit value (crc). We need to force crc to remain a
32-bit value. Attached is a patch though maybe someone
else can think of something better.


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>Comment By: The Written Word (Albert Chin) (tww-china)
Date: 2002-07-02 07:47

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>From zipfile.py:
  ...
  structCentralDir = "<4s4B4H3l5H2l"
  ...
  def _RealGetContents(self):
    ...
            centdir = fp.read(46)
            total = total + 46
            if centdir[0:4] != stringCentralDir:
                raise BadZipfile, "Bad magic number for
central directory"
            centdir = struct.unpack(structCentralDir, centdir)

When a zipfile is created, the CRC is written with:
  def write(self, filename, arcname=None, compress_type=None):
    ...
        self.fp.write(struct.pack("<lll", zinfo.CRC,
zinfo.compress_size,
              zinfo.file_size))

Changing the "3l" to "3L" or "3I" in structCentralDir is
another workaround but as we wrote with "l", we should also
read with "l" (maybe this is the real problem).

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Comment By: The Written Word (Albert Chin) (tww-china)
Date: 2002-07-02 07:42

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Bug #453208 indicates a similar problem.

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Comment By: The Written Word (Albert Chin) (tww-china)
Date: 2002-07-02 07:06

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Do you have access to a machine where sizeof (long) == 8?
Here's what I'm getting:

$ uname -a
OSF1 duh V4.0 878 alpha
$ python
>>> import zipfile
>>> zip = zipfile.ZipFile ('/tmp/a.zip', 'w')
>>> zip.write ('/vmuniz', 'vmunix')
>>> zip.close ()
>>> zip = zipfile.ZipFile ('/tmp/a.zip', 'r')
>>> zip.testzip()
2226205591 -2068761705

I addes some debugging statements to zipfile.read(). The
first number is the output of binascii.crc32() while the
second is the output of zinfo.CRC (the CRC value in the
zipfile header for 'vmuniz' in /tmp/a.zip).

Would binascii.crc32() *ever* return a negative number or
does it return an unsigned type? Looking at the source to
Modules/binascii.c, crc is an unsigned long but the value
returned is signed long.

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Comment By: Tim Peters (tim_one)
Date: 2002-07-02 06:44

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I believe you're having a problem, but I can't tell what it is.  
Exactly how does zipfile.testzip() fail?  What did it get and 
what did it expect?

It's not possible to "force crc to remain a 32-bit value" on a 64-
bit box with sizeof(long)==8 -- Python doesn't have any 32-bit 
type on such a box.  So it seems most likely that some 32-
bit value either is or isn't getting sign-extended when this 
fails, but I can't tell from the report which of the disagreeing 
values that may be, or which it *should* be.

IOW, we need more info about how this fails.  If you're 
hacking the result of binascii.crc32() and calling that "a fix", 
chances seem high that the correct fix lies in changing what 
crc32() returns.  But not yet enough info here to say.

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