Fix Zip64 extensions not being properly applied in some cases

This commit fixes an issue where adding a small file to a `ZipFile`
object while forcing zip64 extensions causes an extra Zip64 record to be
added to the zip, but doesn't update the `min_version` or file sizes.

Fixes #103861

Lib/test/test_zipfile/test_core.py

@@ -1080,6 +1080,43 @@ def test_generated_valid_zip64_extra(self):
                     self.assertEqual(zinfo.header_offset, expected_header_offset)
                     self.assertEqual(zf.read(zinfo), expected_content)
 
+    def test_force_zip64(self):
+        """Test that forcing zip64 extensions correctly notes this in the zip file"""
+        data = io.BytesIO()
+        with zipfile.ZipFile(data, mode="w", allowZip64=True) as zf:
+            with zf.open("text.txt", mode="w", force_zip64=True) as zi:
+                zi.write(b"_")
+
+        zipdata = data.getvalue()
+
+        # check for file header
+        self.assertEqual(zipdata[:4], b"PK\x03\x04")
+
+        # pull out and check file information
+        (
+            vers, os, flags, comp, _, _, crc, csize, usize, fn_len,
+            ex_total_len, filename, ex_id, ex_len, ex_usize, ex_csize
+        ) = struct.unpack("<BB2sHHHIIIHH8shhQQ", zipdata[4:58])
+
+        self.assertGreaterEqual(vers, zipfile.ZIP64_VERSION)  # requires zip64 to extract
+        self.assertEqual(os, 0)  # compatible with MS-DOS
+        self.assertEqual(flags, b"\x00\x00")  # no flags
+        self.assertEqual(comp, 0)  # compression method = stored
+        self.assertEqual(csize, 0xFFFFFFFF)  # sizes are in zip64 extra
+        self.assertEqual(usize, 0xFFFFFFFF)
+        self.assertEqual(fn_len, 8)  # filename len
+        self.assertEqual(ex_total_len, 20)  # size of extra records
+        self.assertEqual(ex_id, 1)  # Zip64 extra record
+        self.assertEqual(ex_len, 16)  # 16 bytes of data
+        self.assertEqual(ex_usize, 1)  # uncompressed size
+        self.assertEqual(ex_csize, 1)  # compressed size
+
+        z = zipfile.ZipFile(io.BytesIO(zipdata))
+        zinfos = z.infolist()
+        self.assertEqual(len(zinfos), 1)
+
+        self.assertGreaterEqual(zinfos[0].extract_version, zipfile.ZIP64_VERSION)  # requires zip64 to extract
+
 
 @requires_zlib()
 class DeflateTestZip64InSmallFiles(AbstractTestZip64InSmallFiles,

Lib/zipfile/__init__.py

@@ -455,17 +455,15 @@ def FileHeader(self, zip64=None):
         extra = self.extra
 
         min_version = 0
-        if zip64 is None:
-            zip64 = file_size > ZIP64_LIMIT or compress_size > ZIP64_LIMIT
+        if (file_size > ZIP64_LIMIT or compress_size > ZIP64_LIMIT):
+            if zip64 is None:
+                zip64 = True
+            elif not zip64:
+                raise LargeZipFile("Filesize would require ZIP64 extensions")
         if zip64:
             fmt = '<HHQQ'
             extra = extra + struct.pack(fmt,
                                         1, struct.calcsize(fmt)-4, file_size, compress_size)
-        if file_size > ZIP64_LIMIT or compress_size > ZIP64_LIMIT:
-            if not zip64:
-                raise LargeZipFile("Filesize would require ZIP64 extensions")
-            # File is larger than what fits into a 4 byte integer,
-            # fall back to the ZIP64 extension
             file_size = 0xffffffff
             compress_size = 0xffffffff
             min_version = ZIP64_VERSION

Misc/NEWS.d/next/Library/2023-04-25-19-58-13.gh-issue-103861.JeozgD.rst

@@ -0,0 +1,2 @@
+Fix ``zipfile.Zipfile`` creating invalid zip files when ``force_zip64`` was
+used to add files to them. Patch by Carey Metcalfe.