1 2XZ Utils To-Do List 3=================== 4 5Known bugs 6---------- 7 8 The test suite is too incomplete. 9 10 If the memory usage limit is less than about 13 MiB, xz is unable to 11 automatically scale down the compression settings enough even though 12 it would be possible by switching from BT2/BT3/BT4 match finder to 13 HC3/HC4. 14 15 XZ Utils compress some files significantly worse than LZMA Utils. 16 This is due to faster compression presets used by XZ Utils, and 17 can often be worked around by using "xz --extreme". With some files 18 --extreme isn't enough though: it's most likely with files that 19 compress extremely well, so going from compression ratio of 0.003 20 to 0.004 means big relative increase in the compressed file size. 21 22 xz doesn't quote unprintable characters when it displays file names 23 given on the command line. 24 25 tuklib_exit() doesn't block signals => EINTR is possible. 26 27 SIGTSTP is not handled. If xz is stopped, the estimated remaining 28 time and calculated (de)compression speed won't make sense in the 29 progress indicator (xz --verbose). 30 31 If liblzma has created threads and fork() gets called, liblzma 32 code will break in the child process unless it calls exec() and 33 doesn't touch liblzma. 34 35 36Missing features 37---------------- 38 39 Add support for storing metadata in .xz files. A preliminary 40 idea is to create a new Stream type for metadata. When both 41 metadata and data are wanted in the same .xz file, two or more 42 Streams would be concatenated. 43 44 The state stored in lzma_stream should be cloneable, which would 45 be mostly useful when using a preset dictionary in LZMA2, but 46 it may have other uses too. Compare to deflateCopy() in zlib. 47 48 Support LZMA_FINISH in raw decoder to indicate end of LZMA1 and 49 other streams that don't have an end of payload marker. 50 51 Adjust dictionary size when the input file size is known. 52 Maybe do this only if an option is given. 53 54 xz doesn't support copying extended attributes, access control 55 lists etc. from source to target file. 56 57 Multithreaded compression: 58 - Reduce memory usage of the current method. 59 - Implement threaded match finders. 60 - Implement pigz-style threading in LZMA2. 61 62 Multithreaded decompression 63 64 Buffer-to-buffer coding could use less RAM (especially when 65 decompressing LZMA1 or LZMA2). 66 67 I/O library is not implemented (similar to gzopen() in zlib). 68 It will be a separate library that supports uncompressed, .gz, 69 .bz2, .lzma, and .xz files. 70 71 Support changing lzma_options_lzma.mode with lzma_filters_update(). 72 73 Support LZMA_FULL_FLUSH for lzma_stream_decoder() to stop at 74 Block and Stream boundaries. 75 76 lzma_strerror() to convert lzma_ret to human readable form? 77 This is tricky, because the same error codes are used with 78 slightly different meanings, and this cannot be fixed anymore. 79 80 Make it possible to adjust LZMA2 options in the middle of a Block 81 so that the encoding speed vs. compression ratio can be optimized 82 when the compressed data is streamed over network. 83 84 Improved BCJ filters. The current filters are small but they aren't 85 so great when compressing binary packages that contain various file 86 types. Specifically, they make things worse if there are static 87 libraries or Linux kernel modules. The filtering could also be 88 more effective (without getting overly complex), for example, 89 streamable variant BCJ2 from 7-Zip could be implemented. 90 91 Filter that autodetects specific data types in the input stream 92 and applies appropriate filters for the corrects parts of the input. 93 Perhaps combine this with the BCJ filter improvement point above. 94 95 Long-range LZ77 method as a separate filter or as a new LZMA2 96 match finder. 97 98 99Documentation 100------------- 101 102 More tutorial programs are needed for liblzma. 103 104 Document the LZMA1 and LZMA2 algorithms. 105 106 107Miscellaneous 108------------ 109 110 Try to get the media type for .xz registered at IANA. 111 112