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linelog: update internal help text This clarifies the details asked by @martinvonz on D3990. Differential Revision: https://phab.mercurial-scm.org/D4147
Gregory Szorc - - Load All Authors

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Version History

1.0.0 (not yet released)

Actions Blocking Release

  • compression and decompression APIs that support io.rawIOBase interface (#13).
  • Refactor module names so C and CFFI extensions live under zstandard package.
  • Overall API design review.
  • Use Python allocator where possible.
  • Figure out what to do about experimental APIs not implemented by CFFI.
  • APIs for auto adjusting compression parameters based on input size. e.g. clamping the window log so it isn't too large for input.
  • Consider allowing compressor and decompressor instances to be thread safe, support concurrent operations. Or track when an operation is in progress and refuse to let concurrent operations use the same instance.
  • Support for magic-less frames for all decompression operations (decompress() doesn't work due to sniffing the content size and the lack of a ZSTD API to sniff magic-less frames - this should be fixed in 1.3.5.).
  • Audit for complete flushing when ending compression streams.
  • Deprecate legacy APIs.
  • Audit for ability to control read/write sizes on all APIs.
  • Detect memory leaks via bench.py.
  • Remove low-level compression parameters from ZstdCompressor.__init__ and require use of CompressionParameters.
  • Expose ZSTD_getFrameProgression() from more compressor types.

Other Actions Not Blocking Release

  • Support for block compression APIs.
  • API for ensuring max memory ceiling isn't exceeded.
  • Move off nose for testing.

0.9.0 (released 2018-04-08)

Backwards Compatibility Notes

  • CFFI 1.11 or newer is now required (previous requirement was 1.8).
  • The primary module is now zstandard. Please change imports of zstd and zstd_cffi to import zstandard. See the README for more. Support for importing the old names will be dropped in the next release.
  • ZstdCompressor.read_from() and ZstdDecompressor.read_from() have been renamed to read_to_iter(). read_from() is aliased to the new name and will be deleted in a future release.
  • Support for Python 2.6 has been removed.
  • Support for Python 3.3 has been removed.
  • The selectivity argument to train_dictionary() has been removed, as the feature disappeared from zstd 1.3.
  • Support for legacy dictionaries has been removed. Cover dictionaries are now the default. train_cover_dictionary() has effectively been renamed to train_dictionary().
  • The allow_empty argument from ZstdCompressor.compress() has been deleted and the method now allows empty inputs to be compressed by default.
  • estimate_compression_context_size() has been removed. Use CompressionParameters.estimated_compression_context_size() instead.
  • get_compression_parameters() has been removed. Use CompressionParameters.from_level() instead.
  • The arguments to CompressionParameters.__init__() have changed. If you were using positional arguments before, the positions now map to different arguments. It is recommended to use keyword arguments to construct CompressionParameters instances.
  • TARGETLENGTH_MAX constant has been removed (it disappeared from zstandard 1.3.4).
  • ZstdCompressor.write_to() and ZstdDecompressor.write_to() have been renamed to ZstdCompressor.stream_writer() and ZstdDecompressor.stream_writer(), respectively. The old names are still aliased, but will be removed in the next major release.
  • Content sizes are written into frame headers by default (ZstdCompressor(write_content_size=True) is now the default).
  • CompressionParameters has been renamed to ZstdCompressionParameters for consistency with other types. The old name is an alias and will be removed in the next major release.

Bug Fixes

  • Fixed memory leak in ZstdCompressor.copy_stream() (#40) (from 0.8.2).
  • Fixed memory leak in ZstdDecompressor.copy_stream() (#35) (from 0.8.2).
  • Fixed memory leak of ZSTD_DDict instances in CFFI's ZstdDecompressor.

New Features

  • Bundlded zstandard library upgraded from 1.1.3 to 1.3.4. This delivers various bug fixes and performance improvements. It also gives us access to newer features.
  • Support for negative compression levels.
  • Support for long distance matching (facilitates compression ratios that approach LZMA).
  • Supporting for reading empty zstandard frames (with an embedded content size of 0).
  • Support for writing and partial support for reading zstandard frames without a magic header.
  • New stream_reader() API that exposes the io.RawIOBase interface (allows you to .read() from a file-like object).
  • Several minor features, bug fixes, and performance enhancements.
  • Wheels for Linux and macOS are now provided with releases.

Changes

  • Functions accepting bytes data now use the buffer protocol and can accept more types (like memoryview and bytearray) (#26).
  • Add #includes so compilation on OS X and BSDs works (#20).
  • New ZstdDecompressor.stream_reader() API to obtain a read-only i/o stream of decompressed data for a source.
  • New ZstdCompressor.stream_reader() API to obtain a read-only i/o stream of compressed data for a source.
  • Renamed ZstdDecompressor.read_from() to ZstdDecompressor.read_to_iter(). The old name is still available.
  • Renamed ZstdCompressor.read_from() to ZstdCompressor.read_to_iter(). read_from() is still available at its old location.
  • Introduce the zstandard module to import and re-export the C or CFFI backend as appropriate. Behavior can be controlled via the PYTHON_ZSTANDARD_IMPORT_POLICY environment variable. See README for usage info.
  • Vendored version of zstd upgraded to 1.3.4.
  • Added module constants CONTENTSIZE_UNKNOWN and CONTENTSIZE_ERROR.
  • Add STRATEGY_BTULTRA compression strategy constant.
  • Switch from deprecated ZSTD_getDecompressedSize() to ZSTD_getFrameContentSize() replacement.
  • ZstdCompressor.compress() can now compress empty inputs without requiring special handling.
  • ZstdCompressor and ZstdDecompressor now have a memory_size() method for determining the current memory utilization of the underlying zstd primitive.
  • train_dictionary() has new arguments and functionality for trying multiple variations of COVER parameters and selecting the best one.
  • Added module constants LDM_MINMATCH_MIN, LDM_MINMATCH_MAX, and LDM_BUCKETSIZELOG_MAX.
  • Converted all consumers to the zstandard new advanced API, which uses ZSTD_compress_generic()
  • CompressionParameters.__init__ now accepts several more arguments, including support for long distance matching.
  • ZstdCompressionDict.__init__ now accepts a dict_type argument that controls how the dictionary should be interpreted. This can be used to force the use of content-only dictionaries or to require the presence of the dictionary magic header.
  • ZstdCompressionDict.precompute_compress() can be used to precompute the compression dictionary so it can efficiently be used with multiple ZstdCompressor instances.
  • Digested dictionaries are now stored in ZstdCompressionDict instances, created automatically on first use, and automatically reused by all ZstdDecompressor instances bound to that dictionary.
  • All meaningful functions now accept keyword arguments.
  • ZstdDecompressor.decompressobj() now accepts a write_size argument to control how much work to perform on every decompressor invocation.
  • ZstdCompressor.write_to() now exposes a tell(), which exposes the total number of bytes written so far.
  • ZstdDecompressor.stream_reader() now supports seek() when moving forward in the stream.
  • Removed TARGETLENGTH_MAX constant.
  • Added frame_header_size(data) function.
  • Added frame_content_size(data) function.
  • Consumers of ZSTD_decompress* have been switched to the new advanced decompression API.
  • ZstdCompressor and ZstdCompressionParams can now be constructed with negative compression levels.
  • ZstdDecompressor now accepts a max_window_size argument to limit the amount of memory required for decompression operations.
  • FORMAT_ZSTD1 and FORMAT_ZSTD1_MAGICLESS constants to be used with the format compression parameter to control whether the frame magic header is written.
  • ZstdDecompressor now accepts a format argument to control the expected frame format.
  • ZstdCompressor now has a frame_progression() method to return information about the current compression operation.
  • Error messages in CFFI no longer have b'' literals.
  • Compiler warnings and underlying overflow issues on 32-bit platforms have been fixed.
  • Builds in CI now build with compiler warnings as errors. This should hopefully fix new compiler warnings from being introduced.
  • Make ZstdCompressor(write_content_size=True) and CompressionParameters(write_content_size=True) the default.
  • CompressionParameters has been renamed to ZstdCompressionParameters.

0.8.2 (released 2018-02-22)

  • Fixed memory leak in ZstdCompressor.copy_stream() (#40).
  • Fixed memory leak in ZstdDecompressor.copy_stream() (#35).

0.8.1 (released 2017-04-08)

  • Add #includes so compilation on OS X and BSDs works (#20).

0.8.0 (released 2017-03-08)

  • CompressionParameters now has a estimated_compression_context_size() method. zstd.estimate_compression_context_size() is now deprecated and slated for removal.
  • Implemented a lot of fuzzing tests.
  • CompressionParameters instances now perform extra validation by calling ZSTD_checkCParams() at construction time.
  • multi_compress_to_buffer() API for compressing multiple inputs as a single operation, as efficiently as possible.
  • ZSTD_CStream instances are now used across multiple operations on ZstdCompressor instances, resulting in much better performance for APIs that do streaming.
  • ZSTD_DStream instances are now used across multiple operations on ZstdDecompressor instances, resulting in much better performance for APIs that do streaming.
  • train_dictionary() now releases the GIL.
  • Support for training dictionaries using the COVER algorithm.
  • multi_decompress_to_buffer() API for decompressing multiple frames as a single operation, as efficiently as possible.
  • Support for multi-threaded compression.
  • Disable deprecation warnings when compiling CFFI module.
  • Fixed memory leak in train_dictionary().
  • Removed DictParameters type.
  • train_dictionary() now accepts keyword arguments instead of a DictParameters instance to control dictionary generation.

0.7.0 (released 2017-02-07)

  • Added zstd.get_frame_parameters() to obtain info about a zstd frame.
  • Added ZstdDecompressor.decompress_content_dict_chain() for efficient decompression of content-only dictionary chains.
  • CFFI module fully implemented; all tests run against both C extension and CFFI implementation.
  • Vendored version of zstd updated to 1.1.3.
  • Use ZstdDecompressor.decompress() now uses ZSTD_createDDict_byReference() to avoid extra memory allocation of dict data.
  • Add function names to error messages (by using ":name" in PyArg_Parse* functions).
  • Reuse decompression context across operations. Previously, we created a new ZSTD_DCtx for each decompress(). This was measured to slow down decompression by 40-200MB/s. The API guarantees say ZstdDecompressor is not thread safe. So we reuse the ZSTD_DCtx across operations and make things faster in the process.
  • ZstdCompressor.write_to()'s compress() and flush() methods now return number of bytes written.
  • ZstdDecompressor.write_to()'s write() method now returns the number of bytes written to the underlying output object.
  • CompressionParameters instances now expose their values as attributes.
  • CompressionParameters instances no longer are subscriptable nor behave as tuples (backwards incompatible). Use attributes to obtain values.
  • DictParameters instances now expose their values as attributes.

0.6.0 (released 2017-01-14)

  • Support for legacy zstd protocols (build time opt in feature).
  • Automation improvements to test against Python 3.6, latest versions of Tox, more deterministic AppVeyor behavior.
  • CFFI "parser" improved to use a compiler preprocessor instead of rewriting source code manually.
  • Vendored version of zstd updated to 1.1.2.
  • Documentation improvements.
  • Introduce a bench.py script for performing (crude) benchmarks.
  • ZSTD_CCtx instances are now reused across multiple compress() operations.
  • ZstdCompressor.write_to() now has a flush() method.
  • ZstdCompressor.compressobj()'s flush() method now accepts an argument to flush a block (as opposed to ending the stream).
  • Disallow compress(b'') when writing content sizes by default (issue #11).

0.5.2 (released 2016-11-12)

  • more packaging fixes for source distribution

0.5.1 (released 2016-11-12)

  • setup_zstd.py is included in the source distribution

0.5.0 (released 2016-11-10)

  • Vendored version of zstd updated to 1.1.1.
  • Continuous integration for Python 3.6 and 3.7
  • Continuous integration for Conda
  • Added compression and decompression APIs providing similar interfaces to the standard library zlib and bz2 modules. This allows coding to a common interface.
  • ``zstd.__version__` is now defined.
  • read_from() on various APIs now accepts objects implementing the buffer protocol.
  • read_from() has gained a skip_bytes argument. This allows callers to pass in an existing buffer with a header without having to create a slice or a new object.
  • Implemented ZstdCompressionDict.as_bytes().
  • Python's memory allocator is now used instead of malloc().
  • Low-level zstd data structures are reused in more instances, cutting down on overhead for certain operations.
  • distutils boilerplate for obtaining an Extension instance has now been refactored into a standalone setup_zstd.py file. This allows other projects with setup.py files to reuse the distutils code for this project without copying code.
  • The monolithic zstd.c file has been split into a header file defining types and separate .c source files for the implementation.

Older History

2016-08-31 - Zstandard 1.0.0 is released and Gregory starts hacking on a Python extension for use by the Mercurial project. A very hacky prototype is sent to the mercurial-devel list for RFC.

2016-09-03 - Most functionality from Zstandard C API implemented. Source code published on https://github.com/indygreg/python-zstandard. Travis-CI automation configured. 0.0.1 release on PyPI.

2016-09-05 - After the API was rounded out a bit and support for Python 2.6 and 2.7 was added, version 0.1 was released to PyPI.

2016-09-05 - After the compressor and decompressor APIs were changed, 0.2 was released to PyPI.

2016-09-10 - 0.3 is released with a bunch of new features. ZstdCompressor now accepts arguments controlling frame parameters. The source size can now be declared when performing streaming compression. ZstdDecompressor.decompress() is implemented. Compression dictionaries are now cached when using the simple compression and decompression APIs. Memory size APIs added. ZstdCompressor.read_from() and ZstdDecompressor.read_from() have been implemented. This rounds out the major compression/decompression APIs planned by the author.

2016-10-02 - 0.3.3 is released with a bug fix for read_from not fully decoding a zstd frame (issue #2).

2016-10-02 - 0.4.0 is released with zstd 1.1.0, support for custom read and write buffer sizes, and a few bug fixes involving failure to read/write all data when buffer sizes were too small to hold remaining data.

2016-11-10 - 0.5.0 is released with zstd 1.1.1 and other enhancements.