[issue11513] Infinite recursion around raising an exception in tarfile

[R. David Murray]

R. David Murray rdmur...@bitdance.com added the comment:

This fix reveals a second bug.  Without this fix, a non-existent file raises an 
IOError with an appropriate error message, but with the chained exception.  
After this fix, it raises an error that says 'not a gzip file', which while 
technically true is not very helpful :)

The correct IOError message only happened by accident in the original code, but 
we need to fix this second bug in order to fix the first one correctly.  I 
suggest that the test case should read:

  with self.assertRaisesRegex(xxx, IOError) as ex:
  tarfile.open(xxx, self.mode)
  self.assertEqual(ex.exception.errno, errno.ENOENT)

--
nosy: +r.david.murray

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[issue11513] Infinite recursion around raising an exception in tarfile

[Evan Dandrea]

Evan Dandrea e...@ubuntu.com added the comment:

*facepalm* Indeed, thanks for pointing that out and nice catch on the race 
condition.  Attached is a patch to fix the issue as you've suggested, and adds 
a test case for it.

--
keywords: +patch
Added file: 
http://bugs.python.org/file21222/tarfile-fix-multiple-exception-on-enoent.patch

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[issue11513] Infinite recursion around raising an exception in tarfile

[Evan Dandrea]

Changes by Evan Dandrea e...@ubuntu.com:


Added file: 
http://bugs.python.org/file21223/tarfile-fix-multiple-exception-on-enoent.patch

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[issue11513] Infinite recursion around raising an exception in tarfile

[Evan Dandrea]

Changes by Evan Dandrea e...@ubuntu.com:


Removed file: 
http://bugs.python.org/file21222/tarfile-fix-multiple-exception-on-enoent.patch

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[issue11513] Infinite recursion around raising an exception in tarfile

[Evan Dandrea]

New submission from Evan Dandrea e...@ubuntu.com:

Using Python tip from Sunday, I noticed that tarfile does not elegantly handle 
ENOENT by raising a single exception:

 tarfile.TarFile.gzopen('fdsfd', 'r')
Traceback (most recent call last):
  File /home/evan/hg/cpython/Lib/tarfile.py, line 1808, in gzopen
fileobj = gzip.GzipFile(name, mode + b, compresslevel, fileobj)
  File /home/evan/hg/cpython/Lib/gzip.py, line 157, in __init__
fileobj = self.myfileobj = builtins.open(filename, mode or 'rb')
IOError: [Errno 2] No such file or directory: 'fdsfd'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File stdin, line 1, in module
  File /home/evan/hg/cpython/Lib/tarfile.py, line 1812, in gzopen
fileobj.close()
AttributeError: 'NoneType' object has no attribute 'close'

I tried to fix this in a cross-platform way, by attempting to open the file 
before processing it, and letting the with statement handle calling close:

diff -r 955547e57cff Lib/tarfile.py
--- a/Lib/tarfile.pySun Mar 13 19:32:21 2011 +0100
+++ b/Lib/tarfile.pyMon Mar 14 19:33:21 2011 -0400
@@ -1793,6 +1793,10 @@
 if len(mode)  1 or mode not in rw:
 raise ValueError(mode must be 'r' or 'w')
 
+if mode == r:
+# force an exception if the file does not exist.
+with open(name):
+pass
 try:
 import gzip
 gzip.GzipFile

However, this produces infinite recursion:
...
  File /home/evan/hg/cpython/Lib/tarfile.py, line 1738, in open
return func(name, r, fileobj, **kwargs)
  File /home/evan/hg/cpython/Lib/tarfile.py, line 1798, in gzopen
with open(name):
  File /home/evan/hg/cpython/Lib/tarfile.py, line 1738, in open
return func(name, r, fileobj, **kwargs)
RuntimeError: maximum recursion depth exceeded

Curiously, if I force the ValueError in that same function to be triggered (by 
passing a three character string for the mode), that exception is raised fine.  
I am therefore wondering if this is a bug in the exit processing.

Unfortunately, my attempts at producing a general test case have been 
unsuccessful thusfar.

--
components: Interpreter Core
messages: 130932
nosy: ev
priority: normal
severity: normal
status: open
title: Infinite recursion around raising an exception in tarfile

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