[ python-Bugs-1527974 ] tarfile chokes on ipython archive on Windows

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Bugs item #1527974, was opened at 2006-07-24 23:00
Message generated for change (Comment added) made by gustaebel
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Category: Python Library
Group: Python 2.4
Status: Open
Resolution: None
Priority: 5
Submitted By: Arve Knudsen (arve_knudsen)
Assigned to: Nobody/Anonymous (nobody)
Summary: tarfile chokes on ipython archive on Windows

Initial Comment:
I'm trying to extract files from the latest ipython tar
archive, available from
http://ipython.scipy.org/dist/ipython-0.7.2.tar.gz,
using tarfile. This is on Windows XP, using Python
2.4.3. There is only a problem if I open the archive in
stream mode (the "mode" argument to tarfile.open is
"r|gz"), in which case tarfile raises StreamError. I'd
be happy if this error could be sorted out.

The following script should trigger the error:

import tarfile

f = file(r"ipython-0.7.2.tar.gz", "rb")
tar = tarfile.open(fileobj=f, mode="r|gz")
try:
    for m in tar:
        tar.extract(m)
finally:
    tar.close()
    f.close(

The resulting exception:
Traceback (most recent call last):
  File "tst.py", line 7, in ?
    tar.extract(m)
  File "C:\Program Files\Python24\lib\tarfile.py", line
1335, in extract
    self._extract_member(tarinfo, os.path.join(path,
tarinfo.name))
  File "C:\Program Files\Python24\lib\tarfile.py", line
1431, in _extract_member

    self.makelink(tarinfo, targetpath)
  File "C:\Program Files\Python24\lib\tarfile.py", line
1515, in makelink
    self._extract_member(self.getmember(linkpath),
targetpath)
  File "C:\Program Files\Python24\lib\tarfile.py", line
1423, in _extract_member

    self.makefile(tarinfo, targetpath)
  File "C:\Program Files\Python24\lib\tarfile.py", line
1461, in makefile
    copyfileobj(source, target)
  File "C:\Program Files\Python24\lib\tarfile.py", line
158, in copyfileobj
    shutil.copyfileobj(src, dst)
  File "C:\Program Files\Python24\lib\shutil.py", line
22, in copyfileobj
    buf = fsrc.read(length)
  File "C:\Program Files\Python24\lib\tarfile.py", line
551, in _readnormal
    self.fileobj.seek(self.offset + self.pos)
  File "C:\Program Files\Python24\lib\tarfile.py", line
420, in seek
    raise StreamError, "seeking backwards is not allowed"
tarfile.StreamError: seeking backwards is not allowed

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Comment By: Lars Gustäbel (gustaebel)
Date: 2006-07-25 10:42

Message:
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The traceback tells me that there is a hard link inside the
archive which means that a file in the archive is referenced
to twice. This hard link can be extracted only on platforms
that have an os.link() function. On Win32 they're not
supported by the file system, but tarfile works around this
by extracting the referenced file twice. In order to extract
the file the second time it is necessary that tarfile seeks
back in the input file to access the file's data again. But
"seeking backwards is not allowed" when a file is opened in
streaming mode ;-)
If you do not necessarily need streaming mode for your
application, better use "r:gz" or "r" and the problem will
be gone.

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Comment By: Arve Knudsen (arve_knudsen)
Date: 2006-07-25 10:04

Message:
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user_id=1522083

Ok, I've verified now that the problem persists with Python
2.4.4 (from the 2.4 branch in svn). The exact same thing
happens.

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Comment By: Arve Knudsen (arve_knudsen)
Date: 2006-07-25 09:29

Message:
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Well yeah, it appears to be Windows specific. I just tested
on Linux (Ubuntu), also with Python 2.4.3. I'll try 2.4.3+
on Windows to see if it makes any difference. Come to think
of it I think I experienced this problem in that past on
Linux, but then I solved it by repacking ipython. Also, if I
pack it myself on Windows using bsdtar it works fine.

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Comment By: Neal Norwitz (nnorwitz)
Date: 2006-07-25 05:35

Message:
Logged In: YES 
user_id=33168

I tested this on Linux with both 2.5 and 2.4.3+ without
problems.  I believe there were some fixes in this area. 
Could you try testing with the 2.4.3+ current which will
become 2.4.4 (or 2.5b2)?  If this is still a problem, it
looks like it may be Windows specific.

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