contrib/python-zstandard/tests/test_compressor.py

zstd: vendor python-zstandard 0.7.0

Commit 3054ae3a66112970a091d3939fee32c2d0c1a23e from
https://github.com/indygreg/python-zstandard is imported without
modifications (other than removing unwanted files).

The vendored zstd library within has been upgraded from 1.1.2 to
1.1.3. This version introduced new APIs for threads, thread
pools, multi-threaded compression, and a new dictionary
builder (COVER). These features are not yet used by
python-zstandard (or Mercurial for that matter). However,
that will likely change in the next python-zstandard release
(and I think there are opportunities for Mercurial to take
advantage of the multi-threaded APIs).

Relevant to Mercurial, the CFFI bindings are now fully
implemented. This means zstd should "just work" with PyPy
(although I haven't tried). The python-zstandard test suite also
runs all tests against both the C extension and CFFI bindings to
ensure feature parity.

There is also a "decompress_content_dict_chain()" API. This was
derived from discussions with Yann Collet on list about alternate
ways of encoding delta chains.

The change most relevant to Mercurial is a performance enhancement in
the simple decompression API to reuse a data structure across
operations. This makes decompression of multiple inputs significantly
faster. (This scenario occurs when reading revlog delta chains, for
example.)

Using python-zstandard's bench.py to measure the performance
difference...

On changelog chunks in the mozilla-unified repo:

decompress discrete decompress() reuse zctx
1.262243 wall; 1.260000 CPU; 1.260000 user; 0.000000 sys 170.43 MB/s (best of 3)
0.949106 wall; 0.950000 CPU; 0.950000 user; 0.000000 sys 226.66 MB/s (best of 4)

decompress discrete dict decompress() reuse zctx
0.692170 wall; 0.690000 CPU; 0.690000 user; 0.000000 sys 310.80 MB/s (best of 5)
0.437088 wall; 0.440000 CPU; 0.440000 user; 0.000000 sys 492.17 MB/s (best of 7)

On manifest chunks in the mozilla-unified repo:

decompress discrete decompress() reuse zctx
1.367284 wall; 1.370000 CPU; 1.370000 user; 0.000000 sys 274.01 MB/s (best of 3)
1.086831 wall; 1.080000 CPU; 1.080000 user; 0.000000 sys 344.72 MB/s (best of 3)

decompress discrete dict decompress() reuse zctx
0.993272 wall; 0.990000 CPU; 0.990000 user; 0.000000 sys 377.19 MB/s (best of 3)
0.678651 wall; 0.680000 CPU; 0.680000 user; 0.000000 sys 552.06 MB/s (best of 5)

That should make reads on zstd revlogs a bit faster ;)

# no-check-commit

import hashlib
import io
import struct
import sys

try:
    import unittest2 as unittest
except ImportError:
    import unittest

import zstd

from .common import (
    make_cffi,
    OpCountingBytesIO,
)


if sys.version_info[0] >= 3:
    next = lambda it: it.__next__()
else:
    next = lambda it: it.next()


@make_cffi
class TestCompressor(unittest.TestCase):
    def test_level_bounds(self):
        with self.assertRaises(ValueError):
            zstd.ZstdCompressor(level=0)

        with self.assertRaises(ValueError):
            zstd.ZstdCompressor(level=23)


@make_cffi
class TestCompressor_compress(unittest.TestCase):
    def test_compress_empty(self):
        cctx = zstd.ZstdCompressor(level=1)
        result = cctx.compress(b'')
        self.assertEqual(result, b'\x28\xb5\x2f\xfd\x00\x48\x01\x00\x00')
        params = zstd.get_frame_parameters(result)
        self.assertEqual(params.content_size, 0)
        self.assertEqual(params.window_size, 524288)
        self.assertEqual(params.dict_id, 0)
        self.assertFalse(params.has_checksum, 0)

        # TODO should be temporary until https://github.com/facebook/zstd/issues/506
        # is fixed.
        cctx = zstd.ZstdCompressor(write_content_size=True)
        with self.assertRaises(ValueError):
            cctx.compress(b'')

        cctx.compress(b'', allow_empty=True)

    def test_compress_large(self):
        chunks = []
        for i in range(255):
            chunks.append(struct.Struct('>B').pack(i) * 16384)

        cctx = zstd.ZstdCompressor(level=3)
        result = cctx.compress(b''.join(chunks))
        self.assertEqual(len(result), 999)
        self.assertEqual(result[0:4], b'\x28\xb5\x2f\xfd')

        # This matches the test for read_from() below.
        cctx = zstd.ZstdCompressor(level=1)
        result = cctx.compress(b'f' * zstd.COMPRESSION_RECOMMENDED_INPUT_SIZE + b'o')
        self.assertEqual(result, b'\x28\xb5\x2f\xfd\x00\x40\x54\x00\x00'
                                 b'\x10\x66\x66\x01\x00\xfb\xff\x39\xc0'
                                 b'\x02\x09\x00\x00\x6f')

    def test_write_checksum(self):
        cctx = zstd.ZstdCompressor(level=1)
        no_checksum = cctx.compress(b'foobar')
        cctx = zstd.ZstdCompressor(level=1, write_checksum=True)
        with_checksum = cctx.compress(b'foobar')

        self.assertEqual(len(with_checksum), len(no_checksum) + 4)

        no_params = zstd.get_frame_parameters(no_checksum)
        with_params = zstd.get_frame_parameters(with_checksum)

        self.assertFalse(no_params.has_checksum)
        self.assertTrue(with_params.has_checksum)

    def test_write_content_size(self):
        cctx = zstd.ZstdCompressor(level=1)
        no_size = cctx.compress(b'foobar' * 256)
        cctx = zstd.ZstdCompressor(level=1, write_content_size=True)
        with_size = cctx.compress(b'foobar' * 256)

        self.assertEqual(len(with_size), len(no_size) + 1)

        no_params = zstd.get_frame_parameters(no_size)
        with_params = zstd.get_frame_parameters(with_size)
        self.assertEqual(no_params.content_size, 0)
        self.assertEqual(with_params.content_size, 1536)

    def test_no_dict_id(self):
        samples = []
        for i in range(128):
            samples.append(b'foo' * 64)
            samples.append(b'bar' * 64)
            samples.append(b'foobar' * 64)

        d = zstd.train_dictionary(1024, samples)

        cctx = zstd.ZstdCompressor(level=1, dict_data=d)
        with_dict_id = cctx.compress(b'foobarfoobar')

        cctx = zstd.ZstdCompressor(level=1, dict_data=d, write_dict_id=False)
        no_dict_id = cctx.compress(b'foobarfoobar')

        self.assertEqual(len(with_dict_id), len(no_dict_id) + 4)

        no_params = zstd.get_frame_parameters(no_dict_id)
        with_params = zstd.get_frame_parameters(with_dict_id)
        self.assertEqual(no_params.dict_id, 0)
        self.assertEqual(with_params.dict_id, 1584102229)

    def test_compress_dict_multiple(self):
        samples = []
        for i in range(128):
            samples.append(b'foo' * 64)
            samples.append(b'bar' * 64)
            samples.append(b'foobar' * 64)

        d = zstd.train_dictionary(8192, samples)

        cctx = zstd.ZstdCompressor(level=1, dict_data=d)

        for i in range(32):
            cctx.compress(b'foo bar foobar foo bar foobar')


@make_cffi
class TestCompressor_compressobj(unittest.TestCase):
    def test_compressobj_empty(self):
        cctx = zstd.ZstdCompressor(level=1)
        cobj = cctx.compressobj()
        self.assertEqual(cobj.compress(b''), b'')
        self.assertEqual(cobj.flush(),
                         b'\x28\xb5\x2f\xfd\x00\x48\x01\x00\x00')

    def test_compressobj_large(self):
        chunks = []
        for i in range(255):
            chunks.append(struct.Struct('>B').pack(i) * 16384)

        cctx = zstd.ZstdCompressor(level=3)
        cobj = cctx.compressobj()

        result = cobj.compress(b''.join(chunks)) + cobj.flush()
        self.assertEqual(len(result), 999)
        self.assertEqual(result[0:4], b'\x28\xb5\x2f\xfd')

        params = zstd.get_frame_parameters(result)
        self.assertEqual(params.content_size, 0)
        self.assertEqual(params.window_size, 1048576)
        self.assertEqual(params.dict_id, 0)
        self.assertFalse(params.has_checksum)

    def test_write_checksum(self):
        cctx = zstd.ZstdCompressor(level=1)
        cobj = cctx.compressobj()
        no_checksum = cobj.compress(b'foobar') + cobj.flush()
        cctx = zstd.ZstdCompressor(level=1, write_checksum=True)
        cobj = cctx.compressobj()
        with_checksum = cobj.compress(b'foobar') + cobj.flush()

        no_params = zstd.get_frame_parameters(no_checksum)
        with_params = zstd.get_frame_parameters(with_checksum)
        self.assertEqual(no_params.content_size, 0)
        self.assertEqual(with_params.content_size, 0)
        self.assertEqual(no_params.dict_id, 0)
        self.assertEqual(with_params.dict_id, 0)
        self.assertFalse(no_params.has_checksum)
        self.assertTrue(with_params.has_checksum)

        self.assertEqual(len(with_checksum), len(no_checksum) + 4)

    def test_write_content_size(self):
        cctx = zstd.ZstdCompressor(level=1)
        cobj = cctx.compressobj(size=len(b'foobar' * 256))
        no_size = cobj.compress(b'foobar' * 256) + cobj.flush()
        cctx = zstd.ZstdCompressor(level=1, write_content_size=True)
        cobj = cctx.compressobj(size=len(b'foobar' * 256))
        with_size = cobj.compress(b'foobar' * 256) + cobj.flush()

        no_params = zstd.get_frame_parameters(no_size)
        with_params = zstd.get_frame_parameters(with_size)
        self.assertEqual(no_params.content_size, 0)
        self.assertEqual(with_params.content_size, 1536)
        self.assertEqual(no_params.dict_id, 0)
        self.assertEqual(with_params.dict_id, 0)
        self.assertFalse(no_params.has_checksum)
        self.assertFalse(with_params.has_checksum)

        self.assertEqual(len(with_size), len(no_size) + 1)

    def test_compress_after_finished(self):
        cctx = zstd.ZstdCompressor()
        cobj = cctx.compressobj()

        cobj.compress(b'foo')
        cobj.flush()

        with self.assertRaisesRegexp(zstd.ZstdError, 'cannot call compress\(\) after compressor'):
            cobj.compress(b'foo')

        with self.assertRaisesRegexp(zstd.ZstdError, 'compressor object already finished'):
            cobj.flush()

    def test_flush_block_repeated(self):
        cctx = zstd.ZstdCompressor(level=1)
        cobj = cctx.compressobj()

        self.assertEqual(cobj.compress(b'foo'), b'')
        self.assertEqual(cobj.flush(zstd.COMPRESSOBJ_FLUSH_BLOCK),
                         b'\x28\xb5\x2f\xfd\x00\x48\x18\x00\x00foo')
        self.assertEqual(cobj.compress(b'bar'), b'')
        # 3 byte header plus content.
        self.assertEqual(cobj.flush(), b'\x19\x00\x00bar')

    def test_flush_empty_block(self):
        cctx = zstd.ZstdCompressor(write_checksum=True)
        cobj = cctx.compressobj()

        cobj.compress(b'foobar')
        cobj.flush(zstd.COMPRESSOBJ_FLUSH_BLOCK)
        # No-op if no block is active (this is internal to zstd).
        self.assertEqual(cobj.flush(zstd.COMPRESSOBJ_FLUSH_BLOCK), b'')

        trailing = cobj.flush()
        # 3 bytes block header + 4 bytes frame checksum
        self.assertEqual(len(trailing), 7)
        header = trailing[0:3]
        self.assertEqual(header, b'\x01\x00\x00')


@make_cffi
class TestCompressor_copy_stream(unittest.TestCase):
    def test_no_read(self):
        source = object()
        dest = io.BytesIO()

        cctx = zstd.ZstdCompressor()
        with self.assertRaises(ValueError):
            cctx.copy_stream(source, dest)

    def test_no_write(self):
        source = io.BytesIO()
        dest = object()

        cctx = zstd.ZstdCompressor()
        with self.assertRaises(ValueError):
            cctx.copy_stream(source, dest)

    def test_empty(self):
        source = io.BytesIO()
        dest = io.BytesIO()

        cctx = zstd.ZstdCompressor(level=1)
        r, w = cctx.copy_stream(source, dest)
        self.assertEqual(int(r), 0)
        self.assertEqual(w, 9)

        self.assertEqual(dest.getvalue(),
                         b'\x28\xb5\x2f\xfd\x00\x48\x01\x00\x00')

    def test_large_data(self):
        source = io.BytesIO()
        for i in range(255):
            source.write(struct.Struct('>B').pack(i) * 16384)
        source.seek(0)

        dest = io.BytesIO()
        cctx = zstd.ZstdCompressor()
        r, w = cctx.copy_stream(source, dest)

        self.assertEqual(r, 255 * 16384)
        self.assertEqual(w, 999)

        params = zstd.get_frame_parameters(dest.getvalue())
        self.assertEqual(params.content_size, 0)
        self.assertEqual(params.window_size, 1048576)
        self.assertEqual(params.dict_id, 0)
        self.assertFalse(params.has_checksum)

    def test_write_checksum(self):
        source = io.BytesIO(b'foobar')
        no_checksum = io.BytesIO()

        cctx = zstd.ZstdCompressor(level=1)
        cctx.copy_stream(source, no_checksum)

        source.seek(0)
        with_checksum = io.BytesIO()
        cctx = zstd.ZstdCompressor(level=1, write_checksum=True)
        cctx.copy_stream(source, with_checksum)

        self.assertEqual(len(with_checksum.getvalue()),
                         len(no_checksum.getvalue()) + 4)

        no_params = zstd.get_frame_parameters(no_checksum.getvalue())
        with_params = zstd.get_frame_parameters(with_checksum.getvalue())
        self.assertEqual(no_params.content_size, 0)
        self.assertEqual(with_params.content_size, 0)
        self.assertEqual(no_params.dict_id, 0)
        self.assertEqual(with_params.dict_id, 0)
        self.assertFalse(no_params.has_checksum)
        self.assertTrue(with_params.has_checksum)

    def test_write_content_size(self):
        source = io.BytesIO(b'foobar' * 256)
        no_size = io.BytesIO()

        cctx = zstd.ZstdCompressor(level=1)
        cctx.copy_stream(source, no_size)

        source.seek(0)
        with_size = io.BytesIO()
        cctx = zstd.ZstdCompressor(level=1, write_content_size=True)
        cctx.copy_stream(source, with_size)

        # Source content size is unknown, so no content size written.
        self.assertEqual(len(with_size.getvalue()),
                         len(no_size.getvalue()))

        source.seek(0)
        with_size = io.BytesIO()
        cctx.copy_stream(source, with_size, size=len(source.getvalue()))

        # We specified source size, so content size header is present.
        self.assertEqual(len(with_size.getvalue()),
                         len(no_size.getvalue()) + 1)

        no_params = zstd.get_frame_parameters(no_size.getvalue())
        with_params = zstd.get_frame_parameters(with_size.getvalue())
        self.assertEqual(no_params.content_size, 0)
        self.assertEqual(with_params.content_size, 1536)
        self.assertEqual(no_params.dict_id, 0)
        self.assertEqual(with_params.dict_id, 0)
        self.assertFalse(no_params.has_checksum)
        self.assertFalse(with_params.has_checksum)

    def test_read_write_size(self):
        source = OpCountingBytesIO(b'foobarfoobar')
        dest = OpCountingBytesIO()
        cctx = zstd.ZstdCompressor()
        r, w = cctx.copy_stream(source, dest, read_size=1, write_size=1)

        self.assertEqual(r, len(source.getvalue()))
        self.assertEqual(w, 21)
        self.assertEqual(source._read_count, len(source.getvalue()) + 1)
        self.assertEqual(dest._write_count, len(dest.getvalue()))


def compress(data, level):
    buffer = io.BytesIO()
    cctx = zstd.ZstdCompressor(level=level)
    with cctx.write_to(buffer) as compressor:
        compressor.write(data)
    return buffer.getvalue()


@make_cffi
class TestCompressor_write_to(unittest.TestCase):
    def test_empty(self):
        result = compress(b'', 1)
        self.assertEqual(result, b'\x28\xb5\x2f\xfd\x00\x48\x01\x00\x00')

        params = zstd.get_frame_parameters(result)
        self.assertEqual(params.content_size, 0)
        self.assertEqual(params.window_size, 524288)
        self.assertEqual(params.dict_id, 0)
        self.assertFalse(params.has_checksum)

    def test_multiple_compress(self):
        buffer = io.BytesIO()
        cctx = zstd.ZstdCompressor(level=5)
        with cctx.write_to(buffer) as compressor:
            self.assertEqual(compressor.write(b'foo'), 0)
            self.assertEqual(compressor.write(b'bar'), 0)
            self.assertEqual(compressor.write(b'x' * 8192), 0)

        result = buffer.getvalue()
        self.assertEqual(result,
                         b'\x28\xb5\x2f\xfd\x00\x50\x75\x00\x00\x38\x66\x6f'
                         b'\x6f\x62\x61\x72\x78\x01\x00\xfc\xdf\x03\x23')

    def test_dictionary(self):
        samples = []
        for i in range(128):
            samples.append(b'foo' * 64)
            samples.append(b'bar' * 64)
            samples.append(b'foobar' * 64)

        d = zstd.train_dictionary(8192, samples)

        buffer = io.BytesIO()
        cctx = zstd.ZstdCompressor(level=9, dict_data=d)
        with cctx.write_to(buffer) as compressor:
            self.assertEqual(compressor.write(b'foo'), 0)
            self.assertEqual(compressor.write(b'bar'), 0)
            self.assertEqual(compressor.write(b'foo' * 16384), 634)

        compressed = buffer.getvalue()

        params = zstd.get_frame_parameters(compressed)
        self.assertEqual(params.content_size, 0)
        self.assertEqual(params.window_size, 1024)
        self.assertEqual(params.dict_id, d.dict_id())
        self.assertFalse(params.has_checksum)

        self.assertEqual(compressed[0:32],
                         b'\x28\xb5\x2f\xfd\x03\x00\x55\x7b\x6b\x5e\x54\x00'
                         b'\x00\x00\x02\xfc\xf4\xa5\xba\x23\x3f\x85\xb3\x54'
                         b'\x00\x00\x18\x6f\x6f\x66\x01\x00')

        h = hashlib.sha1(compressed).hexdigest()
        self.assertEqual(h, '1c5bcd25181bcd8c1a73ea8773323e0056129f92')

    def test_compression_params(self):
        params = zstd.CompressionParameters(20, 6, 12, 5, 4, 10, zstd.STRATEGY_FAST)

        buffer = io.BytesIO()
        cctx = zstd.ZstdCompressor(compression_params=params)
        with cctx.write_to(buffer) as compressor:
            self.assertEqual(compressor.write(b'foo'), 0)
            self.assertEqual(compressor.write(b'bar'), 0)
            self.assertEqual(compressor.write(b'foobar' * 16384), 0)

        compressed = buffer.getvalue()

        params = zstd.get_frame_parameters(compressed)
        self.assertEqual(params.content_size, 0)
        self.assertEqual(params.window_size, 1048576)
        self.assertEqual(params.dict_id, 0)
        self.assertFalse(params.has_checksum)

        h = hashlib.sha1(compressed).hexdigest()
        self.assertEqual(h, '1ae31f270ed7de14235221a604b31ecd517ebd99')

    def test_write_checksum(self):
        no_checksum = io.BytesIO()
        cctx = zstd.ZstdCompressor(level=1)
        with cctx.write_to(no_checksum) as compressor:
            self.assertEqual(compressor.write(b'foobar'), 0)

        with_checksum = io.BytesIO()
        cctx = zstd.ZstdCompressor(level=1, write_checksum=True)
        with cctx.write_to(with_checksum) as compressor:
            self.assertEqual(compressor.write(b'foobar'), 0)

        no_params = zstd.get_frame_parameters(no_checksum.getvalue())
        with_params = zstd.get_frame_parameters(with_checksum.getvalue())
        self.assertEqual(no_params.content_size, 0)
        self.assertEqual(with_params.content_size, 0)
        self.assertEqual(no_params.dict_id, 0)
        self.assertEqual(with_params.dict_id, 0)
        self.assertFalse(no_params.has_checksum)
        self.assertTrue(with_params.has_checksum)

        self.assertEqual(len(with_checksum.getvalue()),
                         len(no_checksum.getvalue()) + 4)

    def test_write_content_size(self):
        no_size = io.BytesIO()
        cctx = zstd.ZstdCompressor(level=1)
        with cctx.write_to(no_size) as compressor:
            self.assertEqual(compressor.write(b'foobar' * 256), 0)

        with_size = io.BytesIO()
        cctx = zstd.ZstdCompressor(level=1, write_content_size=True)
        with cctx.write_to(with_size) as compressor:
            self.assertEqual(compressor.write(b'foobar' * 256), 0)

        # Source size is not known in streaming mode, so header not
        # written.
        self.assertEqual(len(with_size.getvalue()),
                         len(no_size.getvalue()))

        # Declaring size will write the header.
        with_size = io.BytesIO()
        with cctx.write_to(with_size, size=len(b'foobar' * 256)) as compressor:
            self.assertEqual(compressor.write(b'foobar' * 256), 0)

        no_params = zstd.get_frame_parameters(no_size.getvalue())
        with_params = zstd.get_frame_parameters(with_size.getvalue())
        self.assertEqual(no_params.content_size, 0)
        self.assertEqual(with_params.content_size, 1536)
        self.assertEqual(no_params.dict_id, 0)
        self.assertEqual(with_params.dict_id, 0)
        self.assertFalse(no_params.has_checksum)
        self.assertFalse(with_params.has_checksum)

        self.assertEqual(len(with_size.getvalue()),
                         len(no_size.getvalue()) + 1)

    def test_no_dict_id(self):
        samples = []
        for i in range(128):
            samples.append(b'foo' * 64)
            samples.append(b'bar' * 64)
            samples.append(b'foobar' * 64)

        d = zstd.train_dictionary(1024, samples)

        with_dict_id = io.BytesIO()
        cctx = zstd.ZstdCompressor(level=1, dict_data=d)
        with cctx.write_to(with_dict_id) as compressor:
            self.assertEqual(compressor.write(b'foobarfoobar'), 0)

        cctx = zstd.ZstdCompressor(level=1, dict_data=d, write_dict_id=False)
        no_dict_id = io.BytesIO()
        with cctx.write_to(no_dict_id) as compressor:
            self.assertEqual(compressor.write(b'foobarfoobar'), 0)

        no_params = zstd.get_frame_parameters(no_dict_id.getvalue())
        with_params = zstd.get_frame_parameters(with_dict_id.getvalue())
        self.assertEqual(no_params.content_size, 0)
        self.assertEqual(with_params.content_size, 0)
        self.assertEqual(no_params.dict_id, 0)
        self.assertEqual(with_params.dict_id, d.dict_id())
        self.assertFalse(no_params.has_checksum)
        self.assertFalse(with_params.has_checksum)

        self.assertEqual(len(with_dict_id.getvalue()),
                         len(no_dict_id.getvalue()) + 4)

    def test_memory_size(self):
        cctx = zstd.ZstdCompressor(level=3)
        buffer = io.BytesIO()
        with cctx.write_to(buffer) as compressor:
            size = compressor.memory_size()

        self.assertGreater(size, 100000)

    def test_write_size(self):
        cctx = zstd.ZstdCompressor(level=3)
        dest = OpCountingBytesIO()
        with cctx.write_to(dest, write_size=1) as compressor:
            self.assertEqual(compressor.write(b'foo'), 0)
            self.assertEqual(compressor.write(b'bar'), 0)
            self.assertEqual(compressor.write(b'foobar'), 0)

        self.assertEqual(len(dest.getvalue()), dest._write_count)

    def test_flush_repeated(self):
        cctx = zstd.ZstdCompressor(level=3)
        dest = OpCountingBytesIO()
        with cctx.write_to(dest) as compressor:
            self.assertEqual(compressor.write(b'foo'), 0)
            self.assertEqual(dest._write_count, 0)
            self.assertEqual(compressor.flush(), 12)
            self.assertEqual(dest._write_count, 1)
            self.assertEqual(compressor.write(b'bar'), 0)
            self.assertEqual(dest._write_count, 1)
            self.assertEqual(compressor.flush(), 6)
            self.assertEqual(dest._write_count, 2)
            self.assertEqual(compressor.write(b'baz'), 0)

        self.assertEqual(dest._write_count, 3)

    def test_flush_empty_block(self):
        cctx = zstd.ZstdCompressor(level=3, write_checksum=True)
        dest = OpCountingBytesIO()
        with cctx.write_to(dest) as compressor:
            self.assertEqual(compressor.write(b'foobar' * 8192), 0)
            count = dest._write_count
            offset = dest.tell()
            self.assertEqual(compressor.flush(), 23)
            self.assertGreater(dest._write_count, count)
            self.assertGreater(dest.tell(), offset)
            offset = dest.tell()
            # Ending the write here should cause an empty block to be written
            # to denote end of frame.

        trailing = dest.getvalue()[offset:]
        # 3 bytes block header + 4 bytes frame checksum
        self.assertEqual(len(trailing), 7)

        header = trailing[0:3]
        self.assertEqual(header, b'\x01\x00\x00')


@make_cffi
class TestCompressor_read_from(unittest.TestCase):
    def test_type_validation(self):
        cctx = zstd.ZstdCompressor()

        # Object with read() works.
        for chunk in cctx.read_from(io.BytesIO()):
            pass

        # Buffer protocol works.
        for chunk in cctx.read_from(b'foobar'):
            pass

        with self.assertRaisesRegexp(ValueError, 'must pass an object with a read'):
            for chunk in cctx.read_from(True):
                pass

    def test_read_empty(self):
        cctx = zstd.ZstdCompressor(level=1)

        source = io.BytesIO()
        it = cctx.read_from(source)
        chunks = list(it)
        self.assertEqual(len(chunks), 1)
        compressed = b''.join(chunks)
        self.assertEqual(compressed, b'\x28\xb5\x2f\xfd\x00\x48\x01\x00\x00')

        # And again with the buffer protocol.
        it = cctx.read_from(b'')
        chunks = list(it)
        self.assertEqual(len(chunks), 1)
        compressed2 = b''.join(chunks)
        self.assertEqual(compressed2, compressed)

    def test_read_large(self):
        cctx = zstd.ZstdCompressor(level=1)

        source = io.BytesIO()
        source.write(b'f' * zstd.COMPRESSION_RECOMMENDED_INPUT_SIZE)
        source.write(b'o')
        source.seek(0)

        # Creating an iterator should not perform any compression until
        # first read.
        it = cctx.read_from(source, size=len(source.getvalue()))
        self.assertEqual(source.tell(), 0)

        # We should have exactly 2 output chunks.
        chunks = []
        chunk = next(it)
        self.assertIsNotNone(chunk)
        self.assertEqual(source.tell(), zstd.COMPRESSION_RECOMMENDED_INPUT_SIZE)
        chunks.append(chunk)
        chunk = next(it)
        self.assertIsNotNone(chunk)
        chunks.append(chunk)

        self.assertEqual(source.tell(), len(source.getvalue()))

        with self.assertRaises(StopIteration):
            next(it)

        # And again for good measure.
        with self.assertRaises(StopIteration):
            next(it)

        # We should get the same output as the one-shot compression mechanism.
        self.assertEqual(b''.join(chunks), cctx.compress(source.getvalue()))

        params = zstd.get_frame_parameters(b''.join(chunks))
        self.assertEqual(params.content_size, 0)
        self.assertEqual(params.window_size, 262144)
        self.assertEqual(params.dict_id, 0)
        self.assertFalse(params.has_checksum)

        # Now check the buffer protocol.
        it = cctx.read_from(source.getvalue())
        chunks = list(it)
        self.assertEqual(len(chunks), 2)
        self.assertEqual(b''.join(chunks), cctx.compress(source.getvalue()))

    def test_read_write_size(self):
        source = OpCountingBytesIO(b'foobarfoobar')
        cctx = zstd.ZstdCompressor(level=3)
        for chunk in cctx.read_from(source, read_size=1, write_size=1):
            self.assertEqual(len(chunk), 1)

        self.assertEqual(source._read_count, len(source.getvalue()) + 1)