[pacman-dev] delta support in libalpm

[Henning Garus]

2008/11/14 Nagy Gabor <ngaba at bibl.u-szeged.hu>:
> Idézet Xavier <shiningxc at gmail.com>:
>
>> On Fri, Nov 14, 2008 at 1:02 PM, Nagy Gabor <ngaba at bibl.u-szeged.hu>
>> wrote:
>>>>
>>>> I guess I spoke to soon. I was right concerning xdelta3 using gzip for
>>>> handling gzipped files, however it doesn't use the -n flag. This gives
>>>> us the same behaviour as xdelta1, with one minor difference: Method 1.
>>>> stops working.
>>>
>>> Wait. I don't understand something. If it doesn't use the -n flag, how
>>> can
>>> we produce an md5sum-identical patched file? (The mtime is
>>> unpredictable.)
>>> This poses an extra problem, or not? I just did an effective test on
>>> xdelta3-diffing .tar.gz files and I saw that the patched md5sum indeed
>>> differ from the original one :-( Maybe we should search for a gzip header
>>> manipulation tool...
>>>
>>
>> One of the proposal was to use gzip -n, which should fix this problem.
>
> xdelta1 used(?) "gzip -n" for _patched_ .tar.gz file, xdelta3 doesn't use
> "-n", so setting "-n" for the original .tar.gz file won't help any more.
> Probably xdelta3 also can be configured or patched to use "-n"... Or I may
> completely misunderstood something...
>

xdelta1 uses zlib, my proposal was taking the uncompressed output of
xdelta1 and using gzip -n to compress it. xdelta3 uses gzip, but
without -n. I can't find any  options for external compression, but
the easiest thing to do would be deactivating external compression in
xdelta3 and apply it manually by piping the output through gzip -n.