mirror of https://github.com/evilhero/mylar
88 lines
3.3 KiB
ReStructuredText
88 lines
3.3 KiB
ReStructuredText
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rarfile FAQ
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===========
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.. contents:: Table of Contents
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What are the dependencies?
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--------------------------
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It depends on ``unrar`` command-line utility to do the actual decompression.
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Note that by default it expect it to be in ``PATH``. If unrar
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launching fails, you need to fix this.
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Alternatively, :mod:`rarfile` can use bsdtar_ from libarchive_ as
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decompression backend, but that is a bit problematic as bsdtar_ does not support
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all RAR features.
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.. _bsdtar: https://github.com/libarchive/libarchive/wiki/ManPageBsdtar1
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.. _libarchive: http://www.libarchive.org/
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It depends on cryptography_ or PyCrypto_ modules to process
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archives with password-protected headers.
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.. _cryptography: https://pypi.python.org/pypi/cryptography
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.. _PyCrypto: https://pypi.python.org/pypi/pycrypto
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Does it parse ``unrar`` output to get archive contents?
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-------------------------------------------------------
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No, :mod:`rarfile` parses RAR structure in Python code. Also it can
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read uncompressed files from archive without external utility.
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Will rarfile support wrapping unrarlib/unrar.dll/unrar.so in the future?
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------------------------------------------------------------------------
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No. The current architecture - parsing in Python and decompression with
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command line tools work well across all interesting operating systems
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(Windows/Linux/MacOS), wrapping a library does not bring any advantages.
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Simple execution of command-line tools is also legally simpler situation
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than linking with external library.
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How can I get it work on Windows?
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---------------------------------
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On Windows the ``unrar.exe`` is not in ``PATH`` so simple ``Popen("unrar ..")`` does not work.
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It can be solved several ways:
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1. Add location of ``unrar.exe`` to PATH.
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2. Set :data:`rarfile.UNRAR_TOOL` to full path of ``unrar.exe``.
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3. Copy ``unrar.exe`` to your program directory.
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4. Copy ``unrar.exe`` to system directory that is in PATH, eg. ``C:\Windows``.
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How to avoid the need for user to manually install rarfile/unrar?
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-----------------------------------------------------------------
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Include ``rarfile.py`` and/or ``unrar`` with your application.
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Will it support creating RAR archives?
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--------------------------------------
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No. RARLAB_ is not interested in RAR becoming open format
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and specifically discourages writing RAR creation software.
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In the meantime use either Zip_ (better compatibility) or 7z_ (better compression)
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format for your own archives.
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.. _RARLAB: http://www.rarlab.com/
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.. _Zip: https://en.wikipedia.org/wiki/ZIP_%28file_format%29
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.. _7z: https://en.wikipedia.org/wiki/7z
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What is the USE_EXTRACT_HACK?
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-----------------------------
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RarFile uses ``unrar`` to extract compressed files. But when extracting
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single file from archive containing many entries, ``unrar`` needs to parse
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whole archive until it finds the right entry. This makes random-access
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to entries slow. To avoid that, RarFile remembers location of compressed
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data for each entry and on read it copies it to temporary archive containing
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only data for that one file, thus making ``unrar`` fast.
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The logic is only activated for entries smaller than :data:`rarfile.HACK_SIZE_LIMIT`
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(20M by default). Bigger files are accessed directly from RAR.
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Note - it only works for non-solid archives. So if you care about
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random access to files in your archive, do not create solid archives.
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