extractcode 21.6.1

Why another extractor?

it will extract!

ExtractCode will extract things where other extractors may fail.

• Say you want to extract the tarball of the Linux kernel source code on Windows. It contains paths that are the same when ignoring the case and therefore will not extract OK on Windows: some file may be munged or the extract may file.

• Or a tarball (on any OS) may contain multiple times the exact same path. In these cases the paths showing up earlier in the archive may be “hidden” and overwritten by the same path showing up later in the archive giving the impression that there is only one file.

• Or an archive may be damaged a little but most files can still be extracted.

• Or the extracted files are such permissions that you cannot read them and are not owned by you.

• Or the archive may contain weird paths inluding relative paths that may be problematic to extract.

• Or the archive may contain special file types (character/device files) that may be problematic to extract.

• Or an archive may be a virtual disk or some file system(s) images that would typically need to be mounted to be accessed, and may require root access and guesswork to find out which partition and filesystem are at play and which driver to use.

In all these cases, ExtractCode will extract and try hard do the right thing to obtain the actual archived content when other tools may fail.

It can also extract recursively any type of (nested) archives-in-archives

As a downside, the extracted content may not be exactly what would be expected to use the contained files: for instance … but this it is perfectly OK for file content analysis for software composition or forensic analysis.

Behind the scene, ExtractCode uses multiple tools such as:

• the Python standard library,

• a custom ctypes binding to libarchive,

• the 7zip command line tool, and

• optionally libguestfs on Linux.

With these, it is possible to extract a large number of common and less common archives and compressed file types. ExtractCode tries to extract things in the same way on all supported OSes, including auto-renaming files that would have invalid, non-extractible names on certain filesystems or when there are multiple copies of the same path in a given archive (which is possible in a tar).

The extraction is driven from a “voting” system that considers the file extension(s) and name, the filetype and mimetype (using a ctypes binding to libmagic) to select the most appropriate extractor or decompressor function. It can handle multi-level archives such as tar.gz and can extract recursively any nested archives.

Visit https://aboutcode.org and https://github.com/nexB/ for support and download.

We run CI tests on:

• Azure pipelines https://dev.azure.com/nexB/extractcode/_build

Installation

To install this package with its full capability (where the binaries for 7zip and libarchive are installed), use the full extra option:

pip install extractcode[full]

If you want to use the version of binaries (possibly) provided by your operating system, use the minimal option:

pip install extractcode

In this case, you will need to provide a working and compatible libarchive and 7zip installed and configured in one of these ways such that ExtractCode can find them:

• a typecode-libarchive and typecode-7z plugin: See the standard ones at https://github.com/nexB/scancode-plugins/tree/main/builtins These can either bundle a libarchive library, a 7z executable or expose a system-installed libraries. It does so by providing plugin entry points as scancode_location_provider for extractcode_libarchive that should point to a LocationProviderPlugin subclass with a get_locations() method that must return a mapping with this key:

  • ‘extractcode.libarchive.dll’: the absolute path to a libarchive shared object/DLL

  See for example:

  • https://github.com/nexB/scancode-plugins/blob/4da5fe8a5ab1c87b9b4af9e54d7ad60e289747f5/builtins/extractcode_libarchive-linux/setup.py#L40

  • https://github.com/nexB/scancode-plugins/blob/4da5fe8a5ab1c87b9b4af9e54d7ad60e289747f5/builtins/extractcode_libarchive-linux/src/extractcode_libarchive/__init__.py#L17

  And in the same way, the scancode_location_provider for extractcode_7zip should point to a LocationProviderPlugin subclass with a get_locations() method that must return a mapping with this key:

  • ‘extractcode.sevenzip.exe’: the absolute path to a 7zip executable

  See for example:

  • https://github.com/nexB/scancode-plugins/blob/4da5fe8a5ab1c87b9b4af9e54d7ad60e289747f5/builtins/extractcode_7z-linux/setup.py#L40

  • https://github.com/nexB/scancode-plugins/blob/4da5fe8a5ab1c87b9b4af9e54d7ad60e289747f5/builtins/extractcode_7z-linux/src/extractcode_7z/__init__.py#L18

• use environment variables to point to installed binaries:

  • EXTRACTCODE_LIBARCHIVE_PATH: the absolute path to a libarchive DLL

  • EXTRACTCODE_7Z_PATH: the absolute path to a 7zip executable

• a system-installed libarchive and 7zip executable available in the system PATH.

The supported binary tools versions are:

• libarchive 3.5.x

• 7zip 16.5.x

Development

To set up the development environment:

source configure --dev

To run unit tests:

pytest -vvs -n 2

To clean up development environment:

./configure --clean

To run the command line tool in the activated environment:

./extractcode -h

Configuration with environment variables

ExtractCode will use these environment variables if set:

• EXTRACTCODE_LIBARCHIVE_PATH : the path to the libarchive.so libarchive shared library used to support some of the archive formats. If not provided, ExtractCode will look for a plugin-provided libarchive library path. See https://github.com/nexB/scancode-plugins/tree/main/builtins for such plugins. If no plugin contributes libarchive, then a final attempt is made to look for it in the PATH using standard DLL loading techniques.

• EXTRACTCODE_7Z_PATH : the path to the 7z 7zip executable used to support some of the archive formats. If not provided, ExtractCode will look for a plugin-provided 7z executable path. See https://github.com/nexB/scancode-plugins/tree/main/builtins for such plugins. If no plugin contributes 7z, then a final attempt is made to look for it in the PATH.

• EXTRACTCODE_GUESTFISH_PATH : the path to the guestfish tool from libguestfs to use to extract VM images. If not provided, ExtractCode will look in the PATH for an installed guestfish executable instead.

Adding support for VM images extraction

Adding support for VM images requires the manual installation of the libguestfs-tools system package. This is suported only on Linux. On Debian and Ubuntu you can use this command:

sudo apt-get install libguestfs-tools

On Ubuntu only, an additional manual step is required as the kernel executable file cannot be read by users as required by libguestfish.

Run this command as a temporary and immediate fix:

sudo chmod 0644 /boot/vmlinuz-*
for k in /boot/vmlinuz-*
    do sudo dpkg-statoverride --add --update root root 0644 /boot/vmlinuz-$k
done

You likely want both this temporary fix and a more permanent fix; otherwise each kernel update will revert to the default permissions and ExtractCode will stop working for VM images extraction.

Therefore follow these instructions:

1. As sudo, create the file /etc/kernel/postinst.d/statoverride with this content, devised by Kees Cook (@kees) in https://bugs.launchpad.net/ubuntu/+source/linux/+bug/759725/comments/3

#!/bin/sh
version="$1"
# passing the kernel version is required
[ -z "${version}" ] && exit 0
dpkg-statoverride --update --add root root 0644 /boot/vmlinuz-${version}

2. Set executable permissions:

   sudo chmod +x /etc/kernel/postinst.d/statoverride

See also these links for a complete discussion:

• https://bugs.launchpad.net/ubuntu/+source/linux/+bug/759725

• https://bugzilla.redhat.com/show_bug.cgi?id=1670790

• https://bugs.launchpad.net/ubuntu/+source/libguestfs/+bug/1813662/comments/24

Alternative

These other tools are related and were considered before creating ExtractCode:

These tools provide built-in, original extraction capabilities:

• https://libarchive.org/ (integrated in ExtractCode) (BSD license)

• https://www.7-zip.org/ (integrated in ExtractCode) (LGPL license)

• https://theunarchiver.com/command-line (maintenance status unknown) (LGPL license)

These tools are command line tools wrapping other extraction tools and are similar to ExtractCode but with different goals:

• https://github.com/wummel/patool (wrapper on many CLI tools) (GPL license)

• https://github.com/dtrx-py/dtrx (wrapper on a few CLI tools) (recently revived) (GPL license)