Problem with tarfile module to open *.tar.gz files - unreliable ?

m_ahlenius ahleniusm at gmail.com
Fri Aug 20 13:57:36 CEST 2010


On Aug 20, 5:34 am, Dave Angel <da... at ieee.org> wrote:
> m_ahlenius wrote:
> > Hi,
>
> > I am relatively new to doing serious work in python.  I am using it to
> > access a large number of log files.  Some of the logs get corrupted
> > and I need to detect that when processing them.  This code seems to
> > work for quite a few of the logs (all same structure)  It also
> > correctly identifies some corrupt logs but then it identifies others
> > as being corrupt when they are not.
>
> > example error msg from below code:
>
> > Could not open the log file: '/disk/7-29-04-02-01.console.log.tar.gz'
> > Exception: CRC check\
> >  failed 0x8967e931 != 0x4e5f1036L
>
> > When I manually examine the supposed corrupt log file and use
> > "tar -xzvof /disk/7-29-04-02-01.console.log.tar.gz "  on it, it opens
> > just fine.
>
> > Is there anything wrong with how I am using this module?  (extra code
> > removed for clarity)
>
> >  if tarfile.is_tarfile( file ):
> >         try:
> >             xf = tarfile.open( file, "r:gz" )
> >             for locFile in xf:
> >                 logfile = xf.extractfile( locFile )
> >                 validFileFlag = True
> >                 # iterate through each log file, grab the first and
> > the last lines
> >                 lines = iter( logfile )
> >                 firstLine = lines.next()
> >                 for nextLine in lines:
> >                     ....
> >                         continue
>
> >                 logfile.close()
> >                  ...
> >             xf.close()
> >         except Exception, e:
> >             validFileFlag = False
> >             msg = "\nCould not open the log file: " + repr(file) + "
> > Exception: " + str(e) + "\n"
> >  else:
> >         validFileFlag = False
> >         lTime = extractFileNameTime( file )
> >         msg = ">>>>>>> Warning " + file + " is NOT a valid tar archive
> > \n"
> >         print msg
>
> I haven't used tarfile, but this feels like a problem with the Win/Unix
> line endings.  I'm going to assume you're running on Windows, which
> could trigger the problem I'm going to describe.
>
> You use 'file' to hold something, but don't show us what.  In fact, it's
> a lousy name, since it's already a Python builtin.  But if it's holding  
> fileobj, that you've separately opened, then you need to change that
> open to use mode 'rb'
>
> The problem, if I've guessed right, is that occasionally you'll
> accidentally encounter a 0d0a sequence in the middle of the (binary)
> compressed data.  If you're on Windows, and use the default 'r' mode,
> it'll be changed into a 0a byte.  Thus corrupting the checksum, and
> eventually the contents.
>
> DaveA

Hi,

thanks for the comments - I'll change the variable name.

I am running this on linux so don't think its a Windows issue.  So if
that's the case
is the 0d0a still an issue?

'mark



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