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gh-154481: Fix reading multi-frame Zstandard members in zipfile #154537

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gh-154481: Fix reading multi-frame Zstandard members in zipfile #154537

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30 changes: 30 additions & 0 deletions Lib/test/test_zipfile/test_core.py
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Original file line number Diff line number Diff line change
Expand Up @@ -715,6 +715,36 @@ class ZstdTestsWithSourceFile(AbstractTestsWithSourceFile,
unittest.TestCase):
compression = zipfile.ZIP_ZSTANDARD

def test_read_multiframe(self):
first = b'first frame' * 20
second = b'second frame' * 20
data = first + second

class MultiframeCompressor:
def compress(self, value):
value = bytes(value)
return (zipfile.zstd.compress(value[:len(first)]) +
zipfile.zstd.compress(value[len(first):]))

def flush(self):
return b''

archive = io.BytesIO()
with mock.patch.object(zipfile, '_get_compressor',
return_value=MultiframeCompressor()):
with zipfile.ZipFile(archive, 'w', self.compression) as zipfp:
zipfp.writestr('multiframe', data)

with zipfile.ZipFile(archive) as zipfp:
self.assertEqual(zipfp.read('multiframe'), data)

# Exercise a frame boundary between two reads from the archive.
with zipfile.ZipFile(archive) as zipfp:
with zipfp.open('multiframe') as fp:
fp.MIN_READ_SIZE = 1
self.assertEqual(b''.join(iter(lambda: fp.read(1), b'')),
data)

class AbstractTestZip64InSmallFiles:
# These tests test the ZIP64 functionality without using large files,
# see test_zipfile64 for proper tests.
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11 changes: 11 additions & 0 deletions Lib/zipfile/__init__.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1186,6 +1186,13 @@ def _read1(self, n):
data = self._decompressor.unconsumed_tail
if n > len(data):
data += self._read2(n - len(data))
elif (self._compress_type == ZIP_ZSTANDARD and
self._decompressor.eof):
# Continue with the next Zstandard frame.
data = self._decompressor.unused_data
self._decompressor = _get_decompressor(self._compress_type)
if not data:
data = self._read2(n)
else:
data = self._read2(n)

Expand All @@ -1199,6 +1206,10 @@ def _read1(self, n):
not self._decompressor.unconsumed_tail)
if self._eof:
data += self._decompressor.flush()
elif self._compress_type == ZIP_ZSTANDARD:
data = self._decompressor.decompress(data)
self._eof = (self._compress_left <= 0 and
not self._decompressor.unused_data)
else:
data = self._decompressor.decompress(data)
self._eof = self._decompressor.eof or self._compress_left <= 0
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2026-07-23-19-51-05.gh-issue-154481.6cFDFx.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Fix :mod:`zipfile` to correctly read Zstandard-compressed archive members
that could previously be truncated or incorrectly rejected.
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