https://github.com/python/cpython/commit/048f54dc75d51e8a1c5822ab7b282829519... commit: 048f54dc75d51e8a1c5822ab7b2828295192aaa5 branch: 3.9 author: Miss Islington (bot) <31488909+miss-islington@users.noreply.github.com> committer: GitHub <noreply@github.com> date: 2020-09-28T13:18:47-07:00 summary: bpo-40105: ZipFile truncate in append mode with shorter comment (GH-19337) (cherry picked from commit ff9147d93b868f0e13b9fe14e2a76c2879f6787b) Co-authored-by: Jan Mazur <16736821+mzr@users.noreply.github.com> files: A Misc/NEWS.d/next/Library/2020-04-03-16-13-59.bpo-40105.hfM2c0.rst M Lib/test/test_zipfile.py M Lib/zipfile.py diff --git a/Lib/test/test_zipfile.py b/Lib/test/test_zipfile.py index b7bc218d17a3d..999197a0e32dc 100644 --- a/Lib/test/test_zipfile.py +++ b/Lib/test/test_zipfile.py @@ -1855,11 +1855,14 @@ def test_comments(self): self.assertEqual(zipf.comment, b"an updated comment") # check that comments are correctly shortened in append mode + # and the file is indeed truncated with zipfile.ZipFile(TESTFN,mode="w") as zipf: zipf.comment = b"original comment that's longer" zipf.writestr("foo.txt", "O, for a Muse of Fire!") + original_zip_size = os.path.getsize(TESTFN) with zipfile.ZipFile(TESTFN,mode="a") as zipf: zipf.comment = b"shorter comment" + self.assertTrue(original_zip_size > os.path.getsize(TESTFN)) with zipfile.ZipFile(TESTFN,mode="r") as zipf: self.assertEqual(zipf.comment, b"shorter comment") diff --git a/Lib/zipfile.py b/Lib/zipfile.py index 915698f9e0588..816f8582bbf6d 100644 --- a/Lib/zipfile.py +++ b/Lib/zipfile.py @@ -1918,6 +1918,8 @@ def _write_end_record(self): centDirSize, centDirOffset, len(self._comment)) self.fp.write(endrec) self.fp.write(self._comment) + if self.mode == "a": + self.fp.truncate() self.fp.flush() def _fpclose(self, fp): diff --git a/Misc/NEWS.d/next/Library/2020-04-03-16-13-59.bpo-40105.hfM2c0.rst b/Misc/NEWS.d/next/Library/2020-04-03-16-13-59.bpo-40105.hfM2c0.rst new file mode 100644 index 0000000000000..f71a7a1e697a4 --- /dev/null +++ b/Misc/NEWS.d/next/Library/2020-04-03-16-13-59.bpo-40105.hfM2c0.rst @@ -0,0 +1,2 @@ +ZipFile truncates files to avoid corruption when a shorter comment is provided +in append ("a") mode. Patch by Jan Mazur.