Fix edge cases in checking if zip64 extensions are required

This fixes an issue where if data requiring zip64 extensions was added
to an unseekable stream without specifying `force_zip64=True`, zip64
extensions would not be used and a RuntimeError would not be raised when
closing the file (even though the size would be known at that point).
This would result in successfully writing corrupt zip files.

Deciding if zip64 extensions are required outside of the `FileHeader`
function means that both `FileHeader` and `_ZipWriteFile` will always be
in sync. Previously, the `FileHeader` function could enable zip64
extensions without propagating that decision to the `_ZipWriteFile`
class, which would then not correctly write the data descriptor record
or check for errors on close.

Lib/test/test_zipfile/test_core.py

@@ -1115,6 +1115,92 @@ def test_force_zip64(self):
         self.assertEqual(len(zinfos), 1)
         self.assertGreaterEqual(zinfos[0].extract_version, zipfile.ZIP64_VERSION)  # requires zip64 to extract
 
+    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"""
+
+        def make_zip(fp):
+            with zipfile.ZipFile(fp, mode="w", allowZip64=True) as zf:
+                with zf.open("text.txt", mode="w", force_zip64=False) as zi:
+                    zi.write(b"_" * (zipfile.ZIP64_LIMIT + 1))
+
+        self.assertRaises(RuntimeError, make_zip, io.BytesIO())
+        self.assertRaises(RuntimeError, make_zip, Unseekable(io.BytesIO()))
+
+    def test_zip64_required_not_allowed_fail(self):
+        """Test that trying to add a large file to a zip that doesn't allow zip64 extensions fails on add"""
+        def make_zip(fp):
+            with zipfile.ZipFile(fp, mode="w", allowZip64=False) as zf:
+                # pretend zipfile.ZipInfo.from_file was used to get the name and filesize
+                info = zipfile.ZipInfo("text.txt")
+                info.file_size = zipfile.ZIP64_LIMIT + 1
+                zf.open(info, mode="w")
+
+        self.assertRaises(zipfile.LargeZipFile, make_zip, io.BytesIO())
+        self.assertRaises(zipfile.LargeZipFile, make_zip, Unseekable(io.BytesIO()))
+
+    def test_unseekable_zip_known_filesize(self):
+        """Test that creating a zip without seeking will use zip64 extensions if the file size is provided up-front"""
+
+        file_size = zipfile.ZIP64_LIMIT + 1
+
+        def make_zip(fp):
+            with zipfile.ZipFile(fp, mode="w", allowZip64=True) as zf:
+                # pretend zipfile.ZipInfo.from_file was used to get the name and filesize
+                info = zipfile.ZipInfo("text.txt")
+                info.file_size = file_size
+                with zf.open(info, mode="w", force_zip64=False) as zi:
+                    zi.write(b"_" * file_size)
+            return fp
+
+        # check seekable file information
+        seekable_data = make_zip(io.BytesIO()).getvalue()
+        (
+            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("<4sBBHH8xIIHH8shhQQ{}x4s".format(file_size), seekable_data[:62 + file_size])
+
+        self.assertEqual(header, b"PK\x03\x04")
+        self.assertGreaterEqual(vers, zipfile.ZIP64_VERSION)  # requires zip64 to extract
+        self.assertEqual(os, 0)  # compatible with MS-DOS
+        self.assertEqual(flags, 0)  # no flags set
+        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, file_size)  # uncompressed size
+        self.assertEqual(ex_csize, file_size)  # compressed size
+        self.assertEqual(cd_sig, b"PK\x01\x02") # ensure the central directory header is next
+
+        # check unseekable file information
+        unseekable_data = make_zip(Unseekable(io.BytesIO())).fp.getvalue()
+        (
+            header, vers, os, flags, comp, csize, usize, fn_len,
+            ex_total_len, filename, ex_id, ex_len, ex_usize, ex_csize,
+            dd_header, dd_usize, dd_csize, cd_sig
+        ) = struct.unpack("<4sBBHH8xIIHH8shhQQ{}x4s4xQQ4s".format(file_size), unseekable_data[:86 + file_size])
+
+        self.assertEqual(header, b"PK\x03\x04")
+        self.assertGreaterEqual(vers, zipfile.ZIP64_VERSION)  # requires zip64 to extract
+        self.assertEqual(os, 0)  # compatible with MS-DOS
+        self.assertEqual("{:b}".format(flags), "1000")  # streaming flag set
+        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, 0)  # uncompressed size - 0 to defer to data descriptor
+        self.assertEqual(ex_csize, 0)  # compressed size - 0 to defer to data descriptor
+        self.assertEqual(dd_header, b"PK\07\x08")  # data descriptor
+        self.assertEqual(dd_usize, file_size)  # file size (8 bytes because zip64)
+        self.assertEqual(dd_csize, file_size)  # compressed size (8 bytes because zip64)
+        self.assertEqual(cd_sig, b"PK\x01\x02") # ensure the central directory header is next
+
 
 @requires_zlib()
 class DeflateTestZip64InSmallFiles(AbstractTestZip64InSmallFiles,

Lib/zipfile/__init__.py

@@ -439,7 +439,7 @@ def __repr__(self):
         result.append('>')
         return ''.join(result)
 
-    def FileHeader(self, zip64=None):
+    def FileHeader(self, zip64):
         """Return the per-file header as a bytes object."""
         dt = self.date_time
         dosdate = (dt[0] - 1980) << 9 | dt[1] << 5 | dt[2]
@@ -455,11 +455,6 @@ def FileHeader(self, zip64=None):
         extra = self.extra
 
         min_version = 0
-        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,
@@ -1215,6 +1210,12 @@ def close(self):
             self._zinfo.CRC = self._crc
             self._zinfo.file_size = self._file_size
 
+            if not self._zip64:
+                if self._file_size > ZIP64_LIMIT:
+                    raise RuntimeError("File size too large, try using force_zip64")
+                if self._compress_size > ZIP64_LIMIT:
+                    raise RuntimeError("Compressed size too large, try using force_zip64")
+
             # Write updated header info
             if self._zinfo.flag_bits & _MASK_USE_DATA_DESCRIPTOR:
                 # Write CRC and file sizes after the file data
@@ -1223,13 +1224,6 @@ def close(self):
                     self._zinfo.compress_size, self._zinfo.file_size))
                 self._zipfile.start_dir = self._fileobj.tell()
             else:
-                if not self._zip64:
-                    if self._file_size > ZIP64_LIMIT:
-                        raise RuntimeError(
-                            'File size too large, try using force_zip64')
-                    if self._compress_size > ZIP64_LIMIT:
-                        raise RuntimeError(
-                            'Compressed size too large, try using force_zip64')
                 # Seek backwards and write file header (which will now include
                 # correct CRC and file sizes)
 
@@ -1668,8 +1662,9 @@ def _open_to_write(self, zinfo, force_zip64=False):
             zinfo.external_attr = 0o600 << 16  # permissions: ?rw-------
 
         # Compressed size can be larger than uncompressed size
-        zip64 = self._allowZip64 and \
-                (force_zip64 or zinfo.file_size * 1.05 > ZIP64_LIMIT)
+        zip64 = force_zip64 or (zinfo.file_size * 1.05 > ZIP64_LIMIT)
+        if not self._allowZip64 and zip64:
+            raise LargeZipFile("Filesize would require ZIP64 extensions")
 
         if self._seekable:
             self.fp.seek(self.start_dir)