contrib/python-zstandard/zstd_cffi.py

revset: add depth limit to descendants() (issue5374)

This is naive implementation using two-pass scanning. Tracking descendants
isn't an easy problem if both start and stop depths are specified. It's
impractical to remember all possible depths of each node while scanning from
roots to descendants because the number of depths explodes. Instead, we could
cache (min, max) depths as a good approximation and track ancestors back when
needed, but that's likely to have off-by-one bug.

Since this implementation appears not significantly slower, and is quite
straightforward, I think it's good enough for practical use cases. The time
and space complexity is O(n) ish.

  revisions:
  0) 1-pass scanning with (min, max)-depth cache (worst-case quadratic)
  1) 2-pass scanning (this version)

  repository:
  mozilla-central

  # descendants(0) (for reference)
  *) 0.430353

  # descendants(0, depth=1000)
  0) 0.264889
  1) 0.398289

  # descendants(limit(tip:0, 1, offset=10000), depth=1000)
  0) 0.025478
  1) 0.029099

  # descendants(0, depth=2000, startdepth=1000)
  0) painfully slow (due to quadratic backtracking of ancestors)
  1) 1.531138

# Copyright (c) 2016-present, Gregory Szorc
# All rights reserved.
#
# This software may be modified and distributed under the terms
# of the BSD license. See the LICENSE file for details.

"""Python interface to the Zstandard (zstd) compression library."""

from __future__ import absolute_import, unicode_literals

import os
import sys

from _zstd_cffi import (
    ffi,
    lib,
)

if sys.version_info[0] == 2:
    bytes_type = str
    int_type = long
else:
    bytes_type = bytes
    int_type = int


COMPRESSION_RECOMMENDED_INPUT_SIZE = lib.ZSTD_CStreamInSize()
COMPRESSION_RECOMMENDED_OUTPUT_SIZE = lib.ZSTD_CStreamOutSize()
DECOMPRESSION_RECOMMENDED_INPUT_SIZE = lib.ZSTD_DStreamInSize()
DECOMPRESSION_RECOMMENDED_OUTPUT_SIZE = lib.ZSTD_DStreamOutSize()

new_nonzero = ffi.new_allocator(should_clear_after_alloc=False)


MAX_COMPRESSION_LEVEL = lib.ZSTD_maxCLevel()
MAGIC_NUMBER = lib.ZSTD_MAGICNUMBER
FRAME_HEADER = b'\x28\xb5\x2f\xfd'
ZSTD_VERSION = (lib.ZSTD_VERSION_MAJOR, lib.ZSTD_VERSION_MINOR, lib.ZSTD_VERSION_RELEASE)

WINDOWLOG_MIN = lib.ZSTD_WINDOWLOG_MIN
WINDOWLOG_MAX = lib.ZSTD_WINDOWLOG_MAX
CHAINLOG_MIN = lib.ZSTD_CHAINLOG_MIN
CHAINLOG_MAX = lib.ZSTD_CHAINLOG_MAX
HASHLOG_MIN = lib.ZSTD_HASHLOG_MIN
HASHLOG_MAX = lib.ZSTD_HASHLOG_MAX
HASHLOG3_MAX = lib.ZSTD_HASHLOG3_MAX
SEARCHLOG_MIN = lib.ZSTD_SEARCHLOG_MIN
SEARCHLOG_MAX = lib.ZSTD_SEARCHLOG_MAX
SEARCHLENGTH_MIN = lib.ZSTD_SEARCHLENGTH_MIN
SEARCHLENGTH_MAX = lib.ZSTD_SEARCHLENGTH_MAX
TARGETLENGTH_MIN = lib.ZSTD_TARGETLENGTH_MIN
TARGETLENGTH_MAX = lib.ZSTD_TARGETLENGTH_MAX

STRATEGY_FAST = lib.ZSTD_fast
STRATEGY_DFAST = lib.ZSTD_dfast
STRATEGY_GREEDY = lib.ZSTD_greedy
STRATEGY_LAZY = lib.ZSTD_lazy
STRATEGY_LAZY2 = lib.ZSTD_lazy2
STRATEGY_BTLAZY2 = lib.ZSTD_btlazy2
STRATEGY_BTOPT = lib.ZSTD_btopt

COMPRESSOBJ_FLUSH_FINISH = 0
COMPRESSOBJ_FLUSH_BLOCK = 1


def _cpu_count():
    # os.cpu_count() was introducd in Python 3.4.
    try:
        return os.cpu_count() or 0
    except AttributeError:
        pass

    # Linux.
    try:
        if sys.version_info[0] == 2:
            return os.sysconf(b'SC_NPROCESSORS_ONLN')
        else:
            return os.sysconf(u'SC_NPROCESSORS_ONLN')
    except (AttributeError, ValueError):
        pass

    # TODO implement on other platforms.
    return 0


class ZstdError(Exception):
    pass


class CompressionParameters(object):
    def __init__(self, window_log, chain_log, hash_log, search_log,
                 search_length, target_length, strategy):
        if window_log < WINDOWLOG_MIN or window_log > WINDOWLOG_MAX:
            raise ValueError('invalid window log value')

        if chain_log < CHAINLOG_MIN or chain_log > CHAINLOG_MAX:
            raise ValueError('invalid chain log value')

        if hash_log < HASHLOG_MIN or hash_log > HASHLOG_MAX:
            raise ValueError('invalid hash log value')

        if search_log < SEARCHLOG_MIN or search_log > SEARCHLOG_MAX:
            raise ValueError('invalid search log value')

        if search_length < SEARCHLENGTH_MIN or search_length > SEARCHLENGTH_MAX:
            raise ValueError('invalid search length value')

        if target_length < TARGETLENGTH_MIN or target_length > TARGETLENGTH_MAX:
            raise ValueError('invalid target length value')

        if strategy < STRATEGY_FAST or strategy > STRATEGY_BTOPT:
            raise ValueError('invalid strategy value')

        self.window_log = window_log
        self.chain_log = chain_log
        self.hash_log = hash_log
        self.search_log = search_log
        self.search_length = search_length
        self.target_length = target_length
        self.strategy = strategy

        zresult = lib.ZSTD_checkCParams(self.as_compression_parameters())
        if lib.ZSTD_isError(zresult):
            raise ValueError('invalid compression parameters: %s',
                             ffi.string(lib.ZSTD_getErrorName(zresult)))

    def estimated_compression_context_size(self):
        return lib.ZSTD_estimateCCtxSize(self.as_compression_parameters())

    def as_compression_parameters(self):
        p = ffi.new('ZSTD_compressionParameters *')[0]
        p.windowLog = self.window_log
        p.chainLog = self.chain_log
        p.hashLog = self.hash_log
        p.searchLog = self.search_log
        p.searchLength = self.search_length
        p.targetLength = self.target_length
        p.strategy = self.strategy

        return p

def get_compression_parameters(level, source_size=0, dict_size=0):
    params = lib.ZSTD_getCParams(level, source_size, dict_size)
    return CompressionParameters(window_log=params.windowLog,
                                 chain_log=params.chainLog,
                                 hash_log=params.hashLog,
                                 search_log=params.searchLog,
                                 search_length=params.searchLength,
                                 target_length=params.targetLength,
                                 strategy=params.strategy)


def estimate_compression_context_size(params):
    if not isinstance(params, CompressionParameters):
        raise ValueError('argument must be a CompressionParameters')

    cparams = params.as_compression_parameters()
    return lib.ZSTD_estimateCCtxSize(cparams)


def estimate_decompression_context_size():
    return lib.ZSTD_estimateDCtxSize()


class ZstdCompressionWriter(object):
    def __init__(self, compressor, writer, source_size, write_size):
        self._compressor = compressor
        self._writer = writer
        self._source_size = source_size
        self._write_size = write_size
        self._entered = False
        self._mtcctx = compressor._cctx if compressor._multithreaded else None

    def __enter__(self):
        if self._entered:
            raise ZstdError('cannot __enter__ multiple times')

        if self._mtcctx:
            self._compressor._init_mtcstream(self._source_size)
        else:
            self._compressor._ensure_cstream(self._source_size)
        self._entered = True
        return self

    def __exit__(self, exc_type, exc_value, exc_tb):
        self._entered = False

        if not exc_type and not exc_value and not exc_tb:
            out_buffer = ffi.new('ZSTD_outBuffer *')
            dst_buffer = ffi.new('char[]', self._write_size)
            out_buffer.dst = dst_buffer
            out_buffer.size = self._write_size
            out_buffer.pos = 0

            while True:
                if self._mtcctx:
                    zresult = lib.ZSTDMT_endStream(self._mtcctx, out_buffer)
                else:
                    zresult = lib.ZSTD_endStream(self._compressor._cstream, out_buffer)
                if lib.ZSTD_isError(zresult):
                    raise ZstdError('error ending compression stream: %s' %
                                    ffi.string(lib.ZSTD_getErrorName(zresult)))

                if out_buffer.pos:
                    self._writer.write(ffi.buffer(out_buffer.dst, out_buffer.pos)[:])
                    out_buffer.pos = 0

                if zresult == 0:
                    break

        self._compressor = None

        return False

    def memory_size(self):
        if not self._entered:
            raise ZstdError('cannot determine size of an inactive compressor; '
                            'call when a context manager is active')

        return lib.ZSTD_sizeof_CStream(self._compressor._cstream)

    def write(self, data):
        if not self._entered:
            raise ZstdError('write() must be called from an active context '
                            'manager')

        total_write = 0

        data_buffer = ffi.from_buffer(data)

        in_buffer = ffi.new('ZSTD_inBuffer *')
        in_buffer.src = data_buffer
        in_buffer.size = len(data_buffer)
        in_buffer.pos = 0

        out_buffer = ffi.new('ZSTD_outBuffer *')
        dst_buffer = ffi.new('char[]', self._write_size)
        out_buffer.dst = dst_buffer
        out_buffer.size = self._write_size
        out_buffer.pos = 0

        while in_buffer.pos < in_buffer.size:
            if self._mtcctx:
                zresult = lib.ZSTDMT_compressStream(self._mtcctx, out_buffer,
                                                    in_buffer)
            else:
                zresult = lib.ZSTD_compressStream(self._compressor._cstream, out_buffer,
                                                  in_buffer)
            if lib.ZSTD_isError(zresult):
                raise ZstdError('zstd compress error: %s' %
                                ffi.string(lib.ZSTD_getErrorName(zresult)))

            if out_buffer.pos:
                self._writer.write(ffi.buffer(out_buffer.dst, out_buffer.pos)[:])
                total_write += out_buffer.pos
                out_buffer.pos = 0

        return total_write

    def flush(self):
        if not self._entered:
            raise ZstdError('flush must be called from an active context manager')

        total_write = 0

        out_buffer = ffi.new('ZSTD_outBuffer *')
        dst_buffer = ffi.new('char[]', self._write_size)
        out_buffer.dst = dst_buffer
        out_buffer.size = self._write_size
        out_buffer.pos = 0

        while True:
            if self._mtcctx:
                zresult = lib.ZSTDMT_flushStream(self._mtcctx, out_buffer)
            else:
                zresult = lib.ZSTD_flushStream(self._compressor._cstream, out_buffer)
            if lib.ZSTD_isError(zresult):
                raise ZstdError('zstd compress error: %s' %
                                ffi.string(lib.ZSTD_getErrorName(zresult)))

            if not out_buffer.pos:
                break

            self._writer.write(ffi.buffer(out_buffer.dst, out_buffer.pos)[:])
            total_write += out_buffer.pos
            out_buffer.pos = 0

        return total_write


class ZstdCompressionObj(object):
    def compress(self, data):
        if self._finished:
            raise ZstdError('cannot call compress() after compressor finished')

        data_buffer = ffi.from_buffer(data)
        source = ffi.new('ZSTD_inBuffer *')
        source.src = data_buffer
        source.size = len(data_buffer)
        source.pos = 0

        chunks = []

        while source.pos < len(data):
            if self._mtcctx:
                zresult = lib.ZSTDMT_compressStream(self._mtcctx,
                                                    self._out, source)
            else:
                zresult = lib.ZSTD_compressStream(self._compressor._cstream, self._out,
                                                  source)
            if lib.ZSTD_isError(zresult):
                raise ZstdError('zstd compress error: %s' %
                                ffi.string(lib.ZSTD_getErrorName(zresult)))

            if self._out.pos:
                chunks.append(ffi.buffer(self._out.dst, self._out.pos)[:])
                self._out.pos = 0

        return b''.join(chunks)

    def flush(self, flush_mode=COMPRESSOBJ_FLUSH_FINISH):
        if flush_mode not in (COMPRESSOBJ_FLUSH_FINISH, COMPRESSOBJ_FLUSH_BLOCK):
            raise ValueError('flush mode not recognized')

        if self._finished:
            raise ZstdError('compressor object already finished')

        assert self._out.pos == 0

        if flush_mode == COMPRESSOBJ_FLUSH_BLOCK:
            if self._mtcctx:
                zresult = lib.ZSTDMT_flushStream(self._mtcctx, self._out)
            else:
                zresult = lib.ZSTD_flushStream(self._compressor._cstream, self._out)
            if lib.ZSTD_isError(zresult):
                raise ZstdError('zstd compress error: %s' %
                                ffi.string(lib.ZSTD_getErrorName(zresult)))

            # Output buffer is guaranteed to hold full block.
            assert zresult == 0

            if self._out.pos:
                result = ffi.buffer(self._out.dst, self._out.pos)[:]
                self._out.pos = 0
                return result
            else:
                return b''

        assert flush_mode == COMPRESSOBJ_FLUSH_FINISH
        self._finished = True

        chunks = []

        while True:
            if self._mtcctx:
                zresult = lib.ZSTDMT_endStream(self._mtcctx, self._out)
            else:
                zresult = lib.ZSTD_endStream(self._compressor._cstream, self._out)
            if lib.ZSTD_isError(zresult):
                raise ZstdError('error ending compression stream: %s' %
                                ffi.string(lib.ZSTD_getErroName(zresult)))

            if self._out.pos:
                chunks.append(ffi.buffer(self._out.dst, self._out.pos)[:])
                self._out.pos = 0

            if not zresult:
                break

        return b''.join(chunks)


class ZstdCompressor(object):
    def __init__(self, level=3, dict_data=None, compression_params=None,
                 write_checksum=False, write_content_size=False,
                 write_dict_id=True, threads=0):
        if level < 1:
            raise ValueError('level must be greater than 0')
        elif level > lib.ZSTD_maxCLevel():
            raise ValueError('level must be less than %d' % lib.ZSTD_maxCLevel())

        if threads < 0:
            threads = _cpu_count()

        self._compression_level = level
        self._dict_data = dict_data
        self._cparams = compression_params
        self._fparams = ffi.new('ZSTD_frameParameters *')[0]
        self._fparams.checksumFlag = write_checksum
        self._fparams.contentSizeFlag = write_content_size
        self._fparams.noDictIDFlag = not write_dict_id

        if threads:
            cctx = lib.ZSTDMT_createCCtx(threads)
            if cctx == ffi.NULL:
                raise MemoryError()

            self._cctx = ffi.gc(cctx, lib.ZSTDMT_freeCCtx)
            self._multithreaded = True
        else:
            cctx = lib.ZSTD_createCCtx()
            if cctx == ffi.NULL:
                raise MemoryError()

            self._cctx = ffi.gc(cctx, lib.ZSTD_freeCCtx)
            self._multithreaded = False

        self._cstream = None

    def compress(self, data, allow_empty=False):
        if len(data) == 0 and self._fparams.contentSizeFlag and not allow_empty:
            raise ValueError('cannot write empty inputs when writing content sizes')

        if self._multithreaded and self._dict_data:
            raise ZstdError('compress() cannot be used with both dictionaries and multi-threaded compression')

        if self._multithreaded and self._cparams:
            raise ZstdError('compress() cannot be used with both compression parameters and multi-threaded compression')

        # TODO use a CDict for performance.
        dict_data = ffi.NULL
        dict_size = 0

        if self._dict_data:
            dict_data = self._dict_data.as_bytes()
            dict_size = len(self._dict_data)

        params = ffi.new('ZSTD_parameters *')[0]
        if self._cparams:
            params.cParams = self._cparams.as_compression_parameters()
        else:
            params.cParams = lib.ZSTD_getCParams(self._compression_level, len(data),
                                                 dict_size)
        params.fParams = self._fparams

        dest_size = lib.ZSTD_compressBound(len(data))
        out = new_nonzero('char[]', dest_size)

        if self._multithreaded:
            zresult = lib.ZSTDMT_compressCCtx(self._cctx,
                                              ffi.addressof(out), dest_size,
                                              data, len(data),
                                              self._compression_level)
        else:
            zresult = lib.ZSTD_compress_advanced(self._cctx,
                                                 ffi.addressof(out), dest_size,
                                                 data, len(data),
                                                 dict_data, dict_size,
                                                 params)

        if lib.ZSTD_isError(zresult):
            raise ZstdError('cannot compress: %s' %
                            ffi.string(lib.ZSTD_getErrorName(zresult)))

        return ffi.buffer(out, zresult)[:]

    def compressobj(self, size=0):
        if self._multithreaded:
            self._init_mtcstream(size)
        else:
            self._ensure_cstream(size)

        cobj = ZstdCompressionObj()
        cobj._out = ffi.new('ZSTD_outBuffer *')
        cobj._dst_buffer = ffi.new('char[]', COMPRESSION_RECOMMENDED_OUTPUT_SIZE)
        cobj._out.dst = cobj._dst_buffer
        cobj._out.size = COMPRESSION_RECOMMENDED_OUTPUT_SIZE
        cobj._out.pos = 0
        cobj._compressor = self
        cobj._finished = False

        if self._multithreaded:
            cobj._mtcctx = self._cctx
        else:
            cobj._mtcctx = None

        return cobj

    def copy_stream(self, ifh, ofh, size=0,
                    read_size=COMPRESSION_RECOMMENDED_INPUT_SIZE,
                    write_size=COMPRESSION_RECOMMENDED_OUTPUT_SIZE):

        if not hasattr(ifh, 'read'):
            raise ValueError('first argument must have a read() method')
        if not hasattr(ofh, 'write'):
            raise ValueError('second argument must have a write() method')

        mt = self._multithreaded
        if mt:
            self._init_mtcstream(size)
        else:
            self._ensure_cstream(size)

        in_buffer = ffi.new('ZSTD_inBuffer *')
        out_buffer = ffi.new('ZSTD_outBuffer *')

        dst_buffer = ffi.new('char[]', write_size)
        out_buffer.dst = dst_buffer
        out_buffer.size = write_size
        out_buffer.pos = 0

        total_read, total_write = 0, 0

        while True:
            data = ifh.read(read_size)
            if not data:
                break

            data_buffer = ffi.from_buffer(data)
            total_read += len(data_buffer)
            in_buffer.src = data_buffer
            in_buffer.size = len(data_buffer)
            in_buffer.pos = 0

            while in_buffer.pos < in_buffer.size:
                if mt:
                    zresult = lib.ZSTDMT_compressStream(self._cctx, out_buffer, in_buffer)
                else:
                    zresult = lib.ZSTD_compressStream(self._cstream,
                                                      out_buffer, in_buffer)
                if lib.ZSTD_isError(zresult):
                    raise ZstdError('zstd compress error: %s' %
                                    ffi.string(lib.ZSTD_getErrorName(zresult)))

                if out_buffer.pos:
                    ofh.write(ffi.buffer(out_buffer.dst, out_buffer.pos))
                    total_write += out_buffer.pos
                    out_buffer.pos = 0

        # We've finished reading. Flush the compressor.
        while True:
            if mt:
                zresult = lib.ZSTDMT_endStream(self._cctx, out_buffer)
            else:
                zresult = lib.ZSTD_endStream(self._cstream, out_buffer)
            if lib.ZSTD_isError(zresult):
                raise ZstdError('error ending compression stream: %s' %
                                ffi.string(lib.ZSTD_getErrorName(zresult)))

            if out_buffer.pos:
                ofh.write(ffi.buffer(out_buffer.dst, out_buffer.pos))
                total_write += out_buffer.pos
                out_buffer.pos = 0

            if zresult == 0:
                break

        return total_read, total_write

    def write_to(self, writer, size=0,
                 write_size=COMPRESSION_RECOMMENDED_OUTPUT_SIZE):

        if not hasattr(writer, 'write'):
            raise ValueError('must pass an object with a write() method')

        return ZstdCompressionWriter(self, writer, size, write_size)

    def read_from(self, reader, size=0,
                  read_size=COMPRESSION_RECOMMENDED_INPUT_SIZE,
                  write_size=COMPRESSION_RECOMMENDED_OUTPUT_SIZE):
        if hasattr(reader, 'read'):
            have_read = True
        elif hasattr(reader, '__getitem__'):
            have_read = False
            buffer_offset = 0
            size = len(reader)
        else:
            raise ValueError('must pass an object with a read() method or '
                             'conforms to buffer protocol')

        if self._multithreaded:
            self._init_mtcstream(size)
        else:
            self._ensure_cstream(size)

        in_buffer = ffi.new('ZSTD_inBuffer *')
        out_buffer = ffi.new('ZSTD_outBuffer *')

        in_buffer.src = ffi.NULL
        in_buffer.size = 0
        in_buffer.pos = 0

        dst_buffer = ffi.new('char[]', write_size)
        out_buffer.dst = dst_buffer
        out_buffer.size = write_size
        out_buffer.pos = 0

        while True:
            # We should never have output data sitting around after a previous
            # iteration.
            assert out_buffer.pos == 0

            # Collect input data.
            if have_read:
                read_result = reader.read(read_size)
            else:
                remaining = len(reader) - buffer_offset
                slice_size = min(remaining, read_size)
                read_result = reader[buffer_offset:buffer_offset + slice_size]
                buffer_offset += slice_size

            # No new input data. Break out of the read loop.
            if not read_result:
                break

            # Feed all read data into the compressor and emit output until
            # exhausted.
            read_buffer = ffi.from_buffer(read_result)
            in_buffer.src = read_buffer
            in_buffer.size = len(read_buffer)
            in_buffer.pos = 0

            while in_buffer.pos < in_buffer.size:
                if self._multithreaded:
                    zresult = lib.ZSTDMT_compressStream(self._cctx, out_buffer, in_buffer)
                else:
                    zresult = lib.ZSTD_compressStream(self._cstream, out_buffer, in_buffer)
                if lib.ZSTD_isError(zresult):
                    raise ZstdError('zstd compress error: %s' %
                                    ffi.string(lib.ZSTD_getErrorName(zresult)))

                if out_buffer.pos:
                    data = ffi.buffer(out_buffer.dst, out_buffer.pos)[:]
                    out_buffer.pos = 0
                    yield data

            assert out_buffer.pos == 0

            # And repeat the loop to collect more data.
            continue

        # If we get here, input is exhausted. End the stream and emit what
        # remains.
        while True:
            assert out_buffer.pos == 0
            if self._multithreaded:
                zresult = lib.ZSTDMT_endStream(self._cctx, out_buffer)
            else:
                zresult = lib.ZSTD_endStream(self._cstream, out_buffer)
            if lib.ZSTD_isError(zresult):
                raise ZstdError('error ending compression stream: %s' %
                                ffi.string(lib.ZSTD_getErrorName(zresult)))

            if out_buffer.pos:
                data = ffi.buffer(out_buffer.dst, out_buffer.pos)[:]
                out_buffer.pos = 0
                yield data

            if zresult == 0:
                break

    def _ensure_cstream(self, size):
        if self._cstream:
            zresult = lib.ZSTD_resetCStream(self._cstream, size)
            if lib.ZSTD_isError(zresult):
                raise ZstdError('could not reset CStream: %s' %
                                ffi.string(lib.ZSTD_getErrorName(zresult)))

            return

        cstream = lib.ZSTD_createCStream()
        if cstream == ffi.NULL:
            raise MemoryError()

        cstream = ffi.gc(cstream, lib.ZSTD_freeCStream)

        dict_data = ffi.NULL
        dict_size = 0
        if self._dict_data:
            dict_data = self._dict_data.as_bytes()
            dict_size = len(self._dict_data)

        zparams = ffi.new('ZSTD_parameters *')[0]
        if self._cparams:
            zparams.cParams = self._cparams.as_compression_parameters()
        else:
            zparams.cParams = lib.ZSTD_getCParams(self._compression_level,
                                                  size, dict_size)
        zparams.fParams = self._fparams

        zresult = lib.ZSTD_initCStream_advanced(cstream, dict_data, dict_size,
                                                zparams, size)
        if lib.ZSTD_isError(zresult):
            raise Exception('cannot init CStream: %s' %
                            ffi.string(lib.ZSTD_getErrorName(zresult)))

        self._cstream = cstream

    def _init_mtcstream(self, size):
        assert self._multithreaded

        dict_data = ffi.NULL
        dict_size = 0
        if self._dict_data:
            dict_data = self._dict_data.as_bytes()
            dict_size = len(self._dict_data)

        zparams = ffi.new('ZSTD_parameters *')[0]
        if self._cparams:
            zparams.cParams = self._cparams.as_compression_parameters()
        else:
            zparams.cParams = lib.ZSTD_getCParams(self._compression_level,
                                                  size, dict_size)

        zparams.fParams = self._fparams

        zresult = lib.ZSTDMT_initCStream_advanced(self._cctx, dict_data, dict_size,
                                                  zparams, size)

        if lib.ZSTD_isError(zresult):
            raise ZstdError('cannot init CStream: %s' %
                            ffi.string(lib.ZSTD_getErrorName(zresult)))


class FrameParameters(object):
    def __init__(self, fparams):
        self.content_size = fparams.frameContentSize
        self.window_size = fparams.windowSize
        self.dict_id = fparams.dictID
        self.has_checksum = bool(fparams.checksumFlag)


def get_frame_parameters(data):
    if not isinstance(data, bytes_type):
        raise TypeError('argument must be bytes')

    params = ffi.new('ZSTD_frameParams *')

    zresult = lib.ZSTD_getFrameParams(params, data, len(data))
    if lib.ZSTD_isError(zresult):
        raise ZstdError('cannot get frame parameters: %s' %
                        ffi.string(lib.ZSTD_getErrorName(zresult)))

    if zresult:
        raise ZstdError('not enough data for frame parameters; need %d bytes' %
                        zresult)

    return FrameParameters(params[0])


class ZstdCompressionDict(object):
    def __init__(self, data, k=0, d=0):
        assert isinstance(data, bytes_type)
        self._data = data
        self.k = k
        self.d = d

    def __len__(self):
        return len(self._data)

    def dict_id(self):
        return int_type(lib.ZDICT_getDictID(self._data, len(self._data)))

    def as_bytes(self):
        return self._data


def train_dictionary(dict_size, samples, selectivity=0, level=0,
                     notifications=0, dict_id=0):
    if not isinstance(samples, list):
        raise TypeError('samples must be a list')

    total_size = sum(map(len, samples))

    samples_buffer = new_nonzero('char[]', total_size)
    sample_sizes = new_nonzero('size_t[]', len(samples))

    offset = 0
    for i, sample in enumerate(samples):
        if not isinstance(sample, bytes_type):
            raise ValueError('samples must be bytes')

        l = len(sample)
        ffi.memmove(samples_buffer + offset, sample, l)
        offset += l
        sample_sizes[i] = l

    dict_data = new_nonzero('char[]', dict_size)

    dparams = ffi.new('ZDICT_params_t *')[0]
    dparams.selectivityLevel = selectivity
    dparams.compressionLevel = level
    dparams.notificationLevel = notifications
    dparams.dictID = dict_id

    zresult = lib.ZDICT_trainFromBuffer_advanced(
        ffi.addressof(dict_data), dict_size,
        ffi.addressof(samples_buffer),
        ffi.addressof(sample_sizes, 0), len(samples),
        dparams)

    if lib.ZDICT_isError(zresult):
        raise ZstdError('Cannot train dict: %s' %
                        ffi.string(lib.ZDICT_getErrorName(zresult)))

    return ZstdCompressionDict(ffi.buffer(dict_data, zresult)[:])


def train_cover_dictionary(dict_size, samples, k=0, d=0,
                           notifications=0, dict_id=0, level=0, optimize=False,
                           steps=0, threads=0):
    if not isinstance(samples, list):
        raise TypeError('samples must be a list')

    if threads < 0:
        threads = _cpu_count()

    total_size = sum(map(len, samples))

    samples_buffer = new_nonzero('char[]', total_size)
    sample_sizes = new_nonzero('size_t[]', len(samples))

    offset = 0
    for i, sample in enumerate(samples):
        if not isinstance(sample, bytes_type):
            raise ValueError('samples must be bytes')

        l = len(sample)
        ffi.memmove(samples_buffer + offset, sample, l)
        offset += l
        sample_sizes[i] = l

    dict_data = new_nonzero('char[]', dict_size)

    dparams = ffi.new('COVER_params_t *')[0]
    dparams.k = k
    dparams.d = d
    dparams.steps = steps
    dparams.nbThreads = threads
    dparams.notificationLevel = notifications
    dparams.dictID = dict_id
    dparams.compressionLevel = level

    if optimize:
        zresult = lib.COVER_optimizeTrainFromBuffer(
            ffi.addressof(dict_data), dict_size,
            ffi.addressof(samples_buffer),
            ffi.addressof(sample_sizes, 0), len(samples),
            ffi.addressof(dparams))
    else:
        zresult = lib.COVER_trainFromBuffer(
            ffi.addressof(dict_data), dict_size,
            ffi.addressof(samples_buffer),
            ffi.addressof(sample_sizes, 0), len(samples),
            dparams)

    if lib.ZDICT_isError(zresult):
        raise ZstdError('cannot train dict: %s' %
                        ffi.string(lib.ZDICT_getErrorName(zresult)))

    return ZstdCompressionDict(ffi.buffer(dict_data, zresult)[:],
                               k=dparams.k, d=dparams.d)


class ZstdDecompressionObj(object):
    def __init__(self, decompressor):
        self._decompressor = decompressor
        self._finished = False

    def decompress(self, data):
        if self._finished:
            raise ZstdError('cannot use a decompressobj multiple times')

        assert(self._decompressor._dstream)

        in_buffer = ffi.new('ZSTD_inBuffer *')
        out_buffer = ffi.new('ZSTD_outBuffer *')

        data_buffer = ffi.from_buffer(data)
        in_buffer.src = data_buffer
        in_buffer.size = len(data_buffer)
        in_buffer.pos = 0

        dst_buffer = ffi.new('char[]', DECOMPRESSION_RECOMMENDED_OUTPUT_SIZE)
        out_buffer.dst = dst_buffer
        out_buffer.size = len(dst_buffer)
        out_buffer.pos = 0

        chunks = []

        while in_buffer.pos < in_buffer.size:
            zresult = lib.ZSTD_decompressStream(self._decompressor._dstream,
                                                out_buffer, in_buffer)
            if lib.ZSTD_isError(zresult):
                raise ZstdError('zstd decompressor error: %s' %
                                ffi.string(lib.ZSTD_getErrorName(zresult)))

            if zresult == 0:
                self._finished = True
                self._decompressor = None

            if out_buffer.pos:
                chunks.append(ffi.buffer(out_buffer.dst, out_buffer.pos)[:])
                out_buffer.pos = 0

        return b''.join(chunks)


class ZstdDecompressionWriter(object):
    def __init__(self, decompressor, writer, write_size):
        self._decompressor = decompressor
        self._writer = writer
        self._write_size = write_size
        self._entered = False

    def __enter__(self):
        if self._entered:
            raise ZstdError('cannot __enter__ multiple times')

        self._decompressor._ensure_dstream()
        self._entered = True

        return self

    def __exit__(self, exc_type, exc_value, exc_tb):
        self._entered = False

    def memory_size(self):
        if not self._decompressor._dstream:
            raise ZstdError('cannot determine size of inactive decompressor '
                            'call when context manager is active')

        return lib.ZSTD_sizeof_DStream(self._decompressor._dstream)

    def write(self, data):
        if not self._entered:
            raise ZstdError('write must be called from an active context manager')

        total_write = 0

        in_buffer = ffi.new('ZSTD_inBuffer *')
        out_buffer = ffi.new('ZSTD_outBuffer *')

        data_buffer = ffi.from_buffer(data)
        in_buffer.src = data_buffer
        in_buffer.size = len(data_buffer)
        in_buffer.pos = 0

        dst_buffer = ffi.new('char[]', self._write_size)
        out_buffer.dst = dst_buffer
        out_buffer.size = len(dst_buffer)
        out_buffer.pos = 0

        dstream = self._decompressor._dstream

        while in_buffer.pos < in_buffer.size:
            zresult = lib.ZSTD_decompressStream(dstream, out_buffer, in_buffer)
            if lib.ZSTD_isError(zresult):
                raise ZstdError('zstd decompress error: %s' %
                                ffi.string(lib.ZSTD_getErrorName(zresult)))

            if out_buffer.pos:
                self._writer.write(ffi.buffer(out_buffer.dst, out_buffer.pos)[:])
                total_write += out_buffer.pos
                out_buffer.pos = 0

        return total_write


class ZstdDecompressor(object):
    def __init__(self, dict_data=None):
        self._dict_data = dict_data

        dctx = lib.ZSTD_createDCtx()
        if dctx == ffi.NULL:
            raise MemoryError()

        self._refdctx = ffi.gc(dctx, lib.ZSTD_freeDCtx)
        self._dstream = None

    @property
    def _ddict(self):
        if self._dict_data:
            dict_data = self._dict_data.as_bytes()
            dict_size = len(self._dict_data)

            ddict = lib.ZSTD_createDDict(dict_data, dict_size)
            if ddict == ffi.NULL:
                raise ZstdError('could not create decompression dict')
        else:
            ddict = None

        self.__dict__['_ddict'] = ddict
        return ddict

    def decompress(self, data, max_output_size=0):
        data_buffer = ffi.from_buffer(data)

        orig_dctx = new_nonzero('char[]', lib.ZSTD_sizeof_DCtx(self._refdctx))
        dctx = ffi.cast('ZSTD_DCtx *', orig_dctx)
        lib.ZSTD_copyDCtx(dctx, self._refdctx)

        ddict = self._ddict

        output_size = lib.ZSTD_getDecompressedSize(data_buffer, len(data_buffer))
        if output_size:
            result_buffer = ffi.new('char[]', output_size)
            result_size = output_size
        else:
            if not max_output_size:
                raise ZstdError('input data invalid or missing content size '
                                'in frame header')

            result_buffer = ffi.new('char[]', max_output_size)
            result_size = max_output_size

        if ddict:
            zresult = lib.ZSTD_decompress_usingDDict(dctx,
                                                     result_buffer, result_size,
                                                     data_buffer, len(data_buffer),
                                                     ddict)
        else:
            zresult = lib.ZSTD_decompressDCtx(dctx,
                                              result_buffer, result_size,
                                              data_buffer, len(data_buffer))
        if lib.ZSTD_isError(zresult):
            raise ZstdError('decompression error: %s' %
                            ffi.string(lib.ZSTD_getErrorName(zresult)))
        elif output_size and zresult != output_size:
            raise ZstdError('decompression error: decompressed %d bytes; expected %d' %
                            (zresult, output_size))

        return ffi.buffer(result_buffer, zresult)[:]

    def decompressobj(self):
        self._ensure_dstream()
        return ZstdDecompressionObj(self)

    def read_from(self, reader, read_size=DECOMPRESSION_RECOMMENDED_INPUT_SIZE,
                  write_size=DECOMPRESSION_RECOMMENDED_OUTPUT_SIZE,
                  skip_bytes=0):
        if skip_bytes >= read_size:
            raise ValueError('skip_bytes must be smaller than read_size')

        if hasattr(reader, 'read'):
            have_read = True
        elif hasattr(reader, '__getitem__'):
            have_read = False
            buffer_offset = 0
            size = len(reader)
        else:
            raise ValueError('must pass an object with a read() method or '
                             'conforms to buffer protocol')

        if skip_bytes:
            if have_read:
                reader.read(skip_bytes)
            else:
                if skip_bytes > size:
                    raise ValueError('skip_bytes larger than first input chunk')

                buffer_offset = skip_bytes

        self._ensure_dstream()

        in_buffer = ffi.new('ZSTD_inBuffer *')
        out_buffer = ffi.new('ZSTD_outBuffer *')

        dst_buffer = ffi.new('char[]', write_size)
        out_buffer.dst = dst_buffer
        out_buffer.size = len(dst_buffer)
        out_buffer.pos = 0

        while True:
            assert out_buffer.pos == 0

            if have_read:
                read_result = reader.read(read_size)
            else:
                remaining = size - buffer_offset
                slice_size = min(remaining, read_size)
                read_result = reader[buffer_offset:buffer_offset + slice_size]
                buffer_offset += slice_size

            # No new input. Break out of read loop.
            if not read_result:
                break

            # Feed all read data into decompressor and emit output until
            # exhausted.
            read_buffer = ffi.from_buffer(read_result)
            in_buffer.src = read_buffer
            in_buffer.size = len(read_buffer)
            in_buffer.pos = 0

            while in_buffer.pos < in_buffer.size:
                assert out_buffer.pos == 0

                zresult = lib.ZSTD_decompressStream(self._dstream, out_buffer, in_buffer)
                if lib.ZSTD_isError(zresult):
                    raise ZstdError('zstd decompress error: %s' %
                                    ffi.string(lib.ZSTD_getErrorName(zresult)))

                if out_buffer.pos:
                    data = ffi.buffer(out_buffer.dst, out_buffer.pos)[:]
                    out_buffer.pos = 0
                    yield data

                if zresult == 0:
                    return

            # Repeat loop to collect more input data.
            continue

        # If we get here, input is exhausted.

    def write_to(self, writer, write_size=DECOMPRESSION_RECOMMENDED_OUTPUT_SIZE):
        if not hasattr(writer, 'write'):
            raise ValueError('must pass an object with a write() method')

        return ZstdDecompressionWriter(self, writer, write_size)

    def copy_stream(self, ifh, ofh,
                    read_size=DECOMPRESSION_RECOMMENDED_INPUT_SIZE,
                    write_size=DECOMPRESSION_RECOMMENDED_OUTPUT_SIZE):
        if not hasattr(ifh, 'read'):
            raise ValueError('first argument must have a read() method')
        if not hasattr(ofh, 'write'):
            raise ValueError('second argument must have a write() method')

        self._ensure_dstream()

        in_buffer = ffi.new('ZSTD_inBuffer *')
        out_buffer = ffi.new('ZSTD_outBuffer *')

        dst_buffer = ffi.new('char[]', write_size)
        out_buffer.dst = dst_buffer
        out_buffer.size = write_size
        out_buffer.pos = 0

        total_read, total_write = 0, 0

        # Read all available input.
        while True:
            data = ifh.read(read_size)
            if not data:
                break

            data_buffer = ffi.from_buffer(data)
            total_read += len(data_buffer)
            in_buffer.src = data_buffer
            in_buffer.size = len(data_buffer)
            in_buffer.pos = 0

            # Flush all read data to output.
            while in_buffer.pos < in_buffer.size:
                zresult = lib.ZSTD_decompressStream(self._dstream, out_buffer, in_buffer)
                if lib.ZSTD_isError(zresult):
                    raise ZstdError('zstd decompressor error: %s' %
                                    ffi.string(lib.ZSTD_getErrorName(zresult)))

                if out_buffer.pos:
                    ofh.write(ffi.buffer(out_buffer.dst, out_buffer.pos))
                    total_write += out_buffer.pos
                    out_buffer.pos = 0

            # Continue loop to keep reading.

        return total_read, total_write

    def decompress_content_dict_chain(self, frames):
        if not isinstance(frames, list):
            raise TypeError('argument must be a list')

        if not frames:
            raise ValueError('empty input chain')

        # First chunk should not be using a dictionary. We handle it specially.
        chunk = frames[0]
        if not isinstance(chunk, bytes_type):
            raise ValueError('chunk 0 must be bytes')

        # All chunks should be zstd frames and should have content size set.
        chunk_buffer = ffi.from_buffer(chunk)
        params = ffi.new('ZSTD_frameParams *')
        zresult = lib.ZSTD_getFrameParams(params, chunk_buffer, len(chunk_buffer))
        if lib.ZSTD_isError(zresult):
            raise ValueError('chunk 0 is not a valid zstd frame')
        elif zresult:
            raise ValueError('chunk 0 is too small to contain a zstd frame')

        if not params.frameContentSize:
            raise ValueError('chunk 0 missing content size in frame')

        dctx = lib.ZSTD_createDCtx()
        if dctx == ffi.NULL:
            raise MemoryError()

        dctx = ffi.gc(dctx, lib.ZSTD_freeDCtx)

        last_buffer = ffi.new('char[]', params.frameContentSize)

        zresult = lib.ZSTD_decompressDCtx(dctx, last_buffer, len(last_buffer),
                                          chunk_buffer, len(chunk_buffer))
        if lib.ZSTD_isError(zresult):
            raise ZstdError('could not decompress chunk 0: %s' %
                            ffi.string(lib.ZSTD_getErrorName(zresult)))

        # Special case of chain length of 1
        if len(frames) == 1:
            return ffi.buffer(last_buffer, len(last_buffer))[:]

        i = 1
        while i < len(frames):
            chunk = frames[i]
            if not isinstance(chunk, bytes_type):
                raise ValueError('chunk %d must be bytes' % i)

            chunk_buffer = ffi.from_buffer(chunk)
            zresult = lib.ZSTD_getFrameParams(params, chunk_buffer, len(chunk_buffer))
            if lib.ZSTD_isError(zresult):
                raise ValueError('chunk %d is not a valid zstd frame' % i)
            elif zresult:
                raise ValueError('chunk %d is too small to contain a zstd frame' % i)

            if not params.frameContentSize:
                raise ValueError('chunk %d missing content size in frame' % i)

            dest_buffer = ffi.new('char[]', params.frameContentSize)

            zresult = lib.ZSTD_decompress_usingDict(dctx, dest_buffer, len(dest_buffer),
                                                    chunk_buffer, len(chunk_buffer),
                                                    last_buffer, len(last_buffer))
            if lib.ZSTD_isError(zresult):
                raise ZstdError('could not decompress chunk %d' % i)

            last_buffer = dest_buffer
            i += 1

        return ffi.buffer(last_buffer, len(last_buffer))[:]

    def _ensure_dstream(self):
        if self._dstream:
            zresult = lib.ZSTD_resetDStream(self._dstream)
            if lib.ZSTD_isError(zresult):
                raise ZstdError('could not reset DStream: %s' %
                                ffi.string(lib.ZSTD_getErrorName(zresult)))

            return

        self._dstream = lib.ZSTD_createDStream()
        if self._dstream == ffi.NULL:
            raise MemoryError()

        self._dstream = ffi.gc(self._dstream, lib.ZSTD_freeDStream)

        if self._dict_data:
            zresult = lib.ZSTD_initDStream_usingDict(self._dstream,
                                                     self._dict_data.as_bytes(),
                                                     len(self._dict_data))
        else:
            zresult = lib.ZSTD_initDStream(self._dstream)

        if lib.ZSTD_isError(zresult):
            self._dstream = None
            raise ZstdError('could not initialize DStream: %s' %
                            ffi.string(lib.ZSTD_getErrorName(zresult)))