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quakelab-archive: A program to archive a directory tree

This program takes a directory tree, and creates a compressed archive of the directory tree; along with a text file containing a human-readable, searchable catalog of what was archived.

This program only has two requirements:

  1. Python 3.4 or later, with threading enabled.

  2. A POSIX-compliant OS (which includes Linux).

Point 1 is the reason I wrote this: I wanted it to be able to run in as many places as possible, which meant using only functionality available in stock Python.

Threading is used for performance, allowing a file's data to be passed through checksumming, and then handed off for archiving.

How to use

To use, run like this:

python3 create_pax.py /path/to/archive /output/path

… or …

./create_pax.py /path/to/archive /output/path

In the above example, all files and directories within /path/to/archive would be archived. The archive would be written to /output/path.pax.gz, and the catalog would be written to /output/path.txt. /path/to/archive needs to be a directory; we archive whole directory trees, not files!

NOTE: Only items actually within /path/to/archive will be archived! If you have a symlink pointing outside of the directory tree, the symlink will be archived, but the item being pointed to would only be archived if the real item lives in the directory tree.

Within the archive, all of the items will have the /path/to/archive prefix stripped from their path. But, that information is retained in the catalog (see below)!

The Catalog

The catalog is a UTF-8-encoded text file, listing all of the items that can be found in the archive. Here is an example of what a catalog looks like:

 /b4_2/home/somebody
-rw-rwx---      7682aeda3e660192ade888fd4d5ff1843dd75dd8        33      2011-09-12 13:22:06     .bash_logout
-rw-rwx---      fe919c7cb7478d0e36a923dfc65895d8c90db426        176     2011-09-12 13:22:06     .bash_profile
drwx------      0000000000000000000000000000000000000000        N/A     2015-01-09 11:44:22     .ssh
lrwxrwxrwx      0000000000000000000000000000000000000000        18      2013-08-16 19:37:28     file.tgz -> file_7.3-26.tar.gz

The first line of the catalog is the absolute path of the directory. Each directory has a space at the start, and a blank line immediately before it. That is there in case anyone wants to try parsing the catalog in the future. Basically, if you have a blank line, and the next line starts with a space, you have a new directory!

NOTE: Absolute paths are not stored in the archive. Instead, all paths are relative to the path that was provided on the command-line.

The catalog includes directories, files, and symbolic links. In the above examples, the first two entries are files, the second a directory, and the third a symlink. All items start out with the UNIX-style permissions, shown the same way as if you had run ls -l on a command line.

NOTE: The archive also includes the owner & group of the item, though that information is not included in the catalog.

The second item for each entry is the entry's SHA-1 checksum. Directories and files do not have a checksum, so it is replaced with all zeroes.

The third item for each entry is the size of the item, in bytes. Directories do not have a size, so N/A is used instead. For symlinks, the size of the item is the number of characters in the target of the symlink.

The fourth item for each entry is its modification date.

NOTE: Time zone information is not included in the catalog, but is accounted for in the archive.

The last item is the name. If the item is a symlink, the name will be followed by the target of the symlink.

NOTE: The target of the symlink is not modified. If the symlink is a relative path, referring to an item in directory tree which is being archived, then the symlink should continue to work when the archive is expanded. However, if the symlink is an absolute path, or is pointing to a location outside of the directory tree then the symlink will likely be broken when it is expanded.

The Archive

The archive file is a pax file. The pax format was defined in the POSIX.1-2001 standard, and is preferable for a number of reasons:

  • There are no limitations on path length.

  • Paths are UTF-8 encoded.

  • You can attach additional metadata to archives, and to files, in the form of name-value pairs.

The archive is level-9 GZip-compressed.

Today, almost all tar implementations are able to understand the file format, so expanding the archive is as simple as running…

tar -xzf something.pax.gz