New submission from Wolfgang Maier:
I ran into this:
>>> gzout = gzip.open('test.gz','wb')
>>> gzout.write('abcdefgh') # write expects bytes not str
Traceback (most recent call last):
File "<pyshell#2>", line 1, in <module>
gzout.write('abcdefgh')
File "/usr/lib/python3.4/gzip.py", line 343, in write
self.crc = zlib.crc32(data, self.crc) & 0xffffffff
TypeError: 'str' does not support the buffer interface
>>> gzout.write(b'abcdefgh') # ok, use bytes instead
8
>>> gzout.close()
But now the file is not recognized as valid gzip format anymore (neither by the
gzip module nor by external software):
>>> gzin = gzip.open('test.gz','rb')
>>> next(gzin)
Traceback (most recent call last):
File "<pyshell#32>", line 1, in <module>
next(gzin)
File "/usr/lib/python3.4/gzip.py", line 594, in readline
c = self.read(readsize)
File "/usr/lib/python3.4/gzip.py", line 365, in read
if not self._read(readsize):
File "/usr/lib/python3.4/gzip.py", line 465, in _read
self._read_eof()
File "/usr/lib/python3.4/gzip.py", line 487, in _read_eof
raise OSError("Incorrect length of data produced")
OSError: Incorrect length of data produced
Turns out that gzip.write increased the ISIZE field value by 8 already during
the failed call with the str object, so it is now 16 instead of 8:
>>> raw = open('test.gz','rb')
>>> [n for n in raw.read()] # ISIZE is the fourth last element
[31, 139, 8, 8, 51, 46, 127, 83, 2, 255, 116, 101, 115, 116, 0, 75, 76, 74, 78,
73, 77, 75, 207, 0, 0, 80, 42, 239, 174, 16, 0, 0, 0]
in other words: gzip.GzipFile.write() leaps (and modifies) before it checks its
input argument.
----------
components: Library (Lib)
messages: 218961
nosy: wolma
priority: normal
severity: normal
status: open
title: gzip.write changes trailer ISIZE field before type checking - corrupted
gz file after trying to write string
type: behavior
versions: Python 3.4
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue21560>
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