gh-152486: Fix force_zip64 not honored when writing central directory

Lib/test/test_zipfile/test_core.py

@@ -1197,6 +1197,9 @@ def test_force_zip64(self):
         # sizes to 0xFFFFFFFF to indicate to the extractor that the zip64
         # record should be read. Additionally, it would not set the required
         # version to indicate that zip64 extensions are required to extract it.
+        # GH-152486 describes another issue where force_zip64 was honored only
+        # by the local file entry but not by the central directory for a small
+        # file.
         # This test replicates the situation and reads the raw data to specifically ensure:
         #  - The required extract version is always >= ZIP64_VERSION
         #  - The compressed and uncompressed size in the file headers are both
@@ -1207,8 +1210,9 @@ def test_force_zip64(self):
         # bytes are checked to ensure that they line up with the zip spec.
         # The spec for this can be found at: https://pkware.cachefly.net/webdocs/casestudies/APPNOTE.TXT
         # The relevant sections for this test are:
-        #  - 4.3.7 for local file header
-        #  - 4.5.3 for zip64 extra field
+        #  - 4.3.7  for local file header
+        #  - 4.3.12 for central directory
+        #  - 4.5.3  for zip64 extra field
 
         data = io.BytesIO()
         with zipfile.ZipFile(data, mode="w", allowZip64=True) as zf:
@@ -1217,11 +1221,11 @@ def test_force_zip64(self):
 
         zipdata = data.getvalue()
 
-        # pull out and check zip information
+        # check the local file entry
         (
             header, vers, os, flags, comp, csize, usize, fn_len,
-            ex_total_len, filename, ex_id, ex_len, ex_usize, ex_csize, cd_sig
-        ) = struct.unpack("<4sBBHH8xIIHH8shhQQx4s", zipdata[:63])
+            ex_total_len, filename, ex_id, ex_len, ex_usize, ex_csize
+        ) = struct.unpack("<4sBBHH8xIIHH8sHHQQx", zipdata[:59])
 
         self.assertEqual(header, b"PK\x03\x04")  # local file header
         self.assertGreaterEqual(vers, zipfile.ZIP64_VERSION)  # requires zip64 to extract
@@ -1236,12 +1240,45 @@ def test_force_zip64(self):
         self.assertEqual(ex_len, 16)  # 16 bytes of data
         self.assertEqual(ex_usize, 1)  # uncompressed size
         self.assertEqual(ex_csize, 1)  # compressed size
-        self.assertEqual(cd_sig, b"PK\x01\x02") # ensure the central directory header is next
 
-        z = zipfile.ZipFile(io.BytesIO(zipdata))
-        zinfos = z.infolist()
+        # check the entry in central directory,
+        # which should immediately follow the local file entry
+        (
+            header, v_made, v_ext, os, flags, comp, csize, usize, fn_len,
+            ex_total_len, comment_len, in_attr, local_offset, filename,
+            ex_id, ex_len, ex_usize, ex_csize
+        ) = struct.unpack("<4sBxBBHH8xIIHHH2xH4xI8sHHQQ", zipdata[59:133])
+
+        self.assertEqual(header, b"PK\x01\x02")  # central directory file header
+        self.assertGreaterEqual(v_made, zipfile.ZIP64_VERSION)
+        self.assertGreaterEqual(v_ext, zipfile.ZIP64_VERSION)
+        self.assertEqual(os, 0)
+        self.assertEqual(flags, 0)
+        self.assertEqual(comp, 0)
+        self.assertEqual(csize, 0xFFFFFFFF)
+        self.assertEqual(usize, 0xFFFFFFFF)
+        self.assertEqual(fn_len, 8)
+        self.assertEqual(ex_total_len, 20)
+        self.assertEqual(comment_len, 0)  # no file comment
+        self.assertEqual(local_offset, 0)
+        self.assertEqual(ex_id, 1)
+        self.assertEqual(ex_len, 16)
+        self.assertEqual(ex_usize, 1)
+        self.assertEqual(ex_csize, 1)
+
+        # check the ZipInfo object
+        with zipfile.ZipFile(data) as zf:
+            zinfos = zf.infolist()
+            zinfo = zf.getinfo('text.txt')
+
         self.assertEqual(len(zinfos), 1)
-        self.assertGreaterEqual(zinfos[0].extract_version, zipfile.ZIP64_VERSION)  # requires zip64 to extract
+        self.assertGreaterEqual(zinfo.extract_version, zipfile.ZIP64_VERSION)  # requires zip64 to extract
+        self.assertEqual(zinfo.extra, (
+            b'\x01\x00'
+            b'\x10\x00'
+            b'\x01\x00\x00\x00\x00\x00\x00\x00'
+            b'\x01\x00\x00\x00\x00\x00\x00\x00'
+        ))
 
     def test_unseekable_zip_unknown_filesize(self):
         """Test that creating a zip with/without seeking will raise a RuntimeError if zip64 was required but not used"""
@@ -1448,6 +1485,11 @@ def comparable_zinfo(zinfo):
     # pretending it's always set.
     attrs['flag_bits'] |= 0x800
 
+    # Check decoded data (file size, compressed size) and ignore zip64 subfield
+    # in extra data since is may be inconsistent for a ZipInfo before writing
+    # and one read from a file.
+    attrs['extra'] = zipfile._Extra.strip(attrs['extra'], (1,))
+
     return attrs
 
 _struct_pack = struct.pack

Lib/zipfile/__init__.py

@@ -453,6 +453,7 @@ class ZipInfo:
         'file_size',
         '_raw_time',
         '_end_offset',
+        '_force_zip64',
     )
 
     def __init__(self, filename="NoName", date_time=(1980,1,1,0,0,0)):
@@ -488,6 +489,7 @@ def __init__(self, filename="NoName", date_time=(1980,1,1,0,0,0)):
         self.compress_size = 0          # Size of the compressed file
         self.file_size = 0              # Size of the uncompressed file
         self._end_offset = None         # Start of the next local header or central directory
+        self._force_zip64 = None        # Whether zip64 extension is enforced
         # Other attributes are set by class ZipFile:
         # header_offset         Byte offset to the file header
         # CRC                   CRC-32 of the uncompressed file
@@ -2202,6 +2204,7 @@ def open(self, name, mode="r", pwd=None, *, force_zip64=False):
             zinfo = self.getinfo(name)
 
         if mode == 'w':
+            zinfo._force_zip64 = force_zip64
             return self._open_to_write(zinfo, force_zip64=force_zip64)
 
         if self._writing:
@@ -2646,8 +2649,10 @@ def _write_end_record(self):
             dosdate = (dt[0] - 1980) << 9 | dt[1] << 5 | dt[2]
             dostime = dt[3] << 11 | dt[4] << 5 | (dt[5] // 2)
             extra = []
-            if zinfo.file_size > ZIP64_LIMIT \
-               or zinfo.compress_size > ZIP64_LIMIT:
+            if (zinfo._force_zip64
+                or zinfo.file_size > ZIP64_LIMIT
+                or zinfo.compress_size > ZIP64_LIMIT
+            ):
                 extra.append(zinfo.file_size)
                 extra.append(zinfo.compress_size)
                 file_size = 0xffffffff

Misc/NEWS.d/next/Core_and_Builtins/2026-06-29-01-29-09.gh-issue-152486.Uphik6.rst

@@ -0,0 +1 @@
+Fix an issue where :meth:`~zipfile.ZipFile.open` with ``force_zip64=True`` would write the Zip64 extra field to the local file header but fail to do so in the central directory for small files.