[Lzip-bug] Tarball indexing and plzip

[Dennis Katsonis]

Hello,

I was wondering whether it would be difficult or not, to add
functionality to plzip, or create a variant of it, which had tarball
indexing capabilities like pixz.

https://github.com/vasi/pixz

Pixz allows a more random access to the compressed tarball.  Listing is
very quick, and even extracting a file at the end of a large tarball is
quite fast, not too much slower than extracting it from an uncompressed,
indexed tarball.  A major advantage when extracting select files from an
archived compressed tarball.

The problem with using tar with compression is that you must decompress
the stream until you reach the file you want to extract, if you only
want to extract one or a few files.  You must decompress the entire
stream to list.

Pixz solves this, and I think plzip could do this in a similar manner.
Plzip could detect when it's compressing a tar file, and note which file
within the tarball goes into which compressed member(s).  When
extracting specific files, it would only decompress the members those
files are in and filter to stdout only the relevant tar data, which is
then piped to tar for extraction.  The relevant metadata would be
appended to the end of the .lz file.

I haven't looked into the source code in detail yet, I just wanted to
know whether this reasoning was sound.

Regards,
Dennis