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XZ Utils To-Do List |
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Known bugs |
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The test suite is too incomplete. |
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If the memory usage limit is less than about 13 MiB, xz is unable to |
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automatically scale down the compression settings enough even though |
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it would be possible by switching from BT2/BT3/BT4 match finder to |
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HC3/HC4. |
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XZ Utils compress some files significantly worse than LZMA Utils. |
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This is due to faster compression presets used by XZ Utils, and |
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can often be worked around by using "xz --extreme". With some files |
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compress extremely well, so going from compression ratio of 0.003 |
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to 0.004 means big relative increase in the compressed file size. |
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xz doesn't quote unprintable characters when it displays file names |
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given on the command line. |
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tuklib_exit() doesn't block signals => EINTR is possible. |
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SIGTSTP is not handled. If xz is stopped, the estimated remaining |
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time and calculated (de)compression speed won't make sense in the |
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progress indicator (xz --verbose). |
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If liblzma has created threads and fork() gets called, liblzma |
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code will break in the child process unless it calls exec() and |
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doesn't touch liblzma. |
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Missing features |
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Add support for storing metadata in .xz files. A preliminary |
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idea is to create a new Stream type for metadata. When both |
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metadata and data are wanted in the same .xz file, two or more |
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Streams would be concatenated. |
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The state stored in lzma_stream should be cloneable, which would |
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be mostly useful when using a preset dictionary in LZMA2, but |
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it may have other uses too. Compare to deflateCopy() in zlib. |
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Support LZMA_FINISH in raw decoder to indicate end of LZMA1 and |
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other streams that don't have an end of payload marker. |
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Adjust dictionary size when the input file size is known. |
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Maybe do this only if an option is given. |
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xz doesn't support copying extended attributes, access control |
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lists etc. from source to target file. |
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Multithreaded compression: |
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- Reduce memory usage of the current method. |
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- Implement threaded match finders. |
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- Implement pigz-style threading in LZMA2. |
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Buffer-to-buffer coding could use less RAM (especially when |
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decompressing LZMA1 or LZMA2). |
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I/O library is not implemented (similar to gzopen() in zlib). |
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It will be a separate library that supports uncompressed, .gz, |
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.bz2, .lzma, and .xz files. |
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Support changing lzma_options_lzma.mode with lzma_filters_update(). |
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Support LZMA_FULL_FLUSH for lzma_stream_decoder() to stop at |
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Block and Stream boundaries. |
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lzma_strerror() to convert lzma_ret to human readable form? |
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This is tricky, because the same error codes are used with |
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slightly different meanings, and this cannot be fixed anymore. |
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Make it possible to adjust LZMA2 options in the middle of a Block |
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so that the encoding speed vs. compression ratio can be optimized |
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when the compressed data is streamed over network. |
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Improved BCJ filters. The current filters are small but they aren't |
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so great when compressing binary packages that contain various file |
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types. Specifically, they make things worse if there are static |
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libraries or Linux kernel modules. The filtering could also be |
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more effective (without getting overly complex), for example, |
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streamable variant BCJ2 from 7-Zip could be implemented. |
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Filter that autodetects specific data types in the input stream |
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and applies appropriate filters for the corrects parts of the input. |
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Perhaps combine this with the BCJ filter improvement point above. |
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Long-range LZ77 method as a separate filter or as a new LZMA2 |
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match finder. |
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Documentation |
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------------- |
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More tutorial programs are needed for liblzma. |
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Document the LZMA1 and LZMA2 algorithms. |
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Miscellaneous |
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------------ |
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Try to get the media type for .xz registered at IANA. |
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