Bug#506861: python-debian: support data.tar.xz member

[Stuart Prescott]

tag 506861 + patch
thanks

Hi!

attached is a patch that gives python-debian support for xz-compressed .debs. 
This patch is based on the python3 patches that Colin Watson has been working 
on and has been tested with python 2.6, 2.7, 3.2 and 3.3.

For python < 3.3, the unxz utility from the xz-utils package is used to 
decompress the member which is then fed into the python tarfile module as would 
be done for gz or bz2 members. This is crude but works fine. Perhaps python-
debian and python3-debian (until python 3.3 at least) should Recommend xz-
utils as a result. Perhaps better error handling around the subprocess would 
be advisable for the absence of unxz(1) on the system.

For python 3.3 onwards (i.e. wheezy+1), python's in-built lzma support is used 
with tarfile.

Performance wise, there is very little performance difference between using 
unxz(1) and the lzma python module. There is, however, a consistent 
performance difference between operations on gz and xz members. Extracting the 
copyright file from a small .deb (25 kB) is about 50% slower for an xz-
compressed member than a gz compressed member. For very large .debs (~100 MB), 
it's about a factor of 5 slower. This is true for each python tested, 
irrespective of calls to unxz(1) or use of liblzma.

(the large uuencoded mess in the middle of the patch is hello.deb repacked as 
an xz compressed .deb in the same way as hello-bz2.deb is provided for the 
test suite)

Colin: if the maintainers are happy with this and you do intend to NMU python-
debian so that wheezy has python3-debian, please consider adding this patch to 
your stack.

cheers
Stuart


-- 
Stuart Prescott    http://www.nanonanonano.net/   stuart at nanonanonano.net
Debian Developer   http://www.debian.org/         stuart at debian.org
GPG fingerprint    BE65 FD1E F4EA 08F3 23D4 3C6D 9FE8 B8CD 71C5 D1A8
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