[New-bugs-announce] [issue9720] zipfile writes incorrect local file header for large files in zip64

[Craig de Stigter]

New submission from Craig de Stigter <craig.ds at gmail.com>:

Steps to reproduce:

# create a large (>4gb) file
f = open('foo.txt', 'wb')
text = 'a' * 1024**2
for i in xrange(5 * 1024):
    f.write(text)
f.close()

# now zip the file
import zipfile
z = zipfile.ZipFile('foo.zip', mode='w', allowZip64=True)
z.write('foo.txt')
z.close()


Now inspect the file headers using a hex editor. The written headers are incorrect. The filesize and compressed size should be written as 0xffffffff and the 'extra field' should contain the actual sizes.


Tested on Python 2.5 but looking at the latest code in 3.2 it still looks broken.

The problem is that the ZipInfo.FileHeader() is written before the filesize is populated, so Zip64 extensions are not written. Later, the sizes in the header are written, but Zip64 extensions are not taken into account and the filesize is just wrapped (7gb becomes 3gb, for instance).

My patch fixes the problem on Python 2.5, it might need minor porting to fix trunk. It works by assigning the uncompressed filesize to the ZipInfo header initially, then writing the header. Then later on, I re-write the header (this is okay since the header size will not have increased.)

----------
components: Library (Lib)
files: zipfile_zip64_header.patch
keywords: patch
messages: 115250
nosy: craigds
priority: normal
severity: normal
status: open
title: zipfile writes incorrect local file header for large files in zip64
type: behavior
versions: Python 2.5, Python 2.6, Python 2.7, Python 3.1, Python 3.2, Python 3.3
Added file: http://bugs.python.org/file18685/zipfile_zip64_header.patch

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue9720>
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