Re: [Bug-tar] tar corrupts on append

[Tim Kientzle]

> On Mar 12, 2016, at 8:44 AM, Sergey Poznyakoff <address@hidden> wrote:
> 
> Hi Renate,
> 
>> Here is a test case that clearly fails:
> 
> The test fails because it invokes truncate, which cripples the archive.

No, that's just how Renate was able to create an archive that demonstrates
the bug.  If you look at a hex dump, you'll see that the truncated result is a
valid archive with two blocks of zeros as a valid end-of-archive marker.

> With that part commented out, it runs as expected and produces a correct
> archive.  Tested with 1.28 and git HEAD.

You can also reproduce the bug by playing with the -b option.

#!/bin/sh

# This demonstrates a bug in GNU tar's handling of -r.

gnutar --version

for f in a b c d e f g h i; do
  echo $f>$f
done

echo
echo 'Creating archive with a, b, c'
gnutar -v -cf data -b1 a b c

gnutar -v -tf data

echo
echo 'Adding d, e, f'
gnutar -v -rf data -b3 d e f
gnutar -v -tf data

echo
echo 'Adding g, h, i'
gnutar -v -rf data -b5 g h i
gnutar -v -tf data

######### end of script #########################

Here's the output of the above on an OS X machine using a recent gnutar from 
MacPorts:

tar (GNU tar) 1.28
Copyright (C) 2014 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Written by John Gilmore and Jay Fenlason.

Creating archive with a, b, c
a
b
c
-rw-r--r-- tim/staff         2 2016-03-12 12:35 a
-rw-r--r-- tim/staff         2 2016-03-12 12:35 b
-rw-r--r-- tim/staff         2 2016-03-12 12:35 c

Adding d, e, f
d
e
f
-rw-r--r-- tim/staff         2 2016-03-12 12:35 a
-rw-r--r-- tim/staff         2 2016-03-12 12:35 b
-rw-r--r-- tim/staff         2 2016-03-12 12:35 c
gnutar: Skipping to next header
-rw-r--r-- tim/staff         2 2016-03-12 12:35 e
-rw-r--r-- tim/staff         2 2016-03-12 12:35 f
gnutar: Exiting with failure status due to previous errors

Adding g, h, i
gnutar: Skipping to next header
g
h
i
gnutar: Exiting with failure status due to previous errors
-rw-r--r-- tim/staff         2 2016-03-12 12:35 a
-rw-r--r-- tim/staff         2 2016-03-12 12:35 b
-rw-r--r-- tim/staff         2 2016-03-12 12:35 c
gnutar: Skipping to next header
-rw-r--r-- tim/staff         2 2016-03-12 12:35 e
gnutar: Skipping to next header
-rw-r--r-- tim/staff         2 2016-03-12 12:35 g
gnutar: Skipping to next header
-rw-r--r-- tim/staff         2 2016-03-12 12:35 h
-rw-r--r-- tim/staff         2 2016-03-12 12:35 i
gnutar: Exiting with failure status due to previous errors