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

Author: lpyu001

Lib/test/test_zipfile/test_core.py

@@ -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.

Lib/zipfile/__init__.py

@@ -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)
 
@@ -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

Misc/NEWS.d/next/Library/2026-07-23-19-51-05.gh-issue-154481.6cFDFx.rst

@@ -0,0 +1,2 @@
+Fix :mod:`zipfile` to correctly read Zstandard-compressed archive members
+that could previously be truncated or incorrectly rejected.