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bpo-40105: ZipFile truncate in append mode with shorter comment (GH-19337)

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(cherry picked from commit ff9147d93b)

Co-authored-by: Jan Mazur <16736821+mzr@users.noreply.github.com>
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Miss Islington (bot) 2020-09-28 13:18:47 -07:00 • committed by GitHub
parent bdf46bc7e1
commit 048f54dc75
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3
Lib/test/test_zipfile.py
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@ -1855,11 +1855,14 @@ class OtherTests(unittest.TestCase):
self.assertEqual(zipf.comment, b"an updated comment") self.assertEqual(zipf.comment, b"an updated comment")
# check that comments are correctly shortened in append mode # check that comments are correctly shortened in append mode
# and the file is indeed truncated
with zipfile.ZipFile(TESTFN,mode="w") as zipf: with zipfile.ZipFile(TESTFN,mode="w") as zipf:
zipf.comment = b"original comment that's longer" zipf.comment = b"original comment that's longer"
zipf.writestr("foo.txt", "O, for a Muse of Fire!") 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: with zipfile.ZipFile(TESTFN,mode="a") as zipf:
zipf.comment = b"shorter comment" zipf.comment = b"shorter comment"
self.assertTrue(original_zip_size > os.path.getsize(TESTFN))
with zipfile.ZipFile(TESTFN,mode="r") as zipf: with zipfile.ZipFile(TESTFN,mode="r") as zipf:
self.assertEqual(zipf.comment, b"shorter comment") self.assertEqual(zipf.comment, b"shorter comment")

2
Lib/zipfile.py
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@ -1918,6 +1918,8 @@ class ZipFile:
centDirSize, centDirOffset, len(self._comment)) centDirSize, centDirOffset, len(self._comment))
self.fp.write(endrec) self.fp.write(endrec)
self.fp.write(self._comment) self.fp.write(self._comment)
if self.mode == "a":
self.fp.truncate()
self.fp.flush() self.fp.flush()
def _fpclose(self, fp): def _fpclose(self, fp):

2
Misc/NEWS.d/next/Library/2020-04-03-16-13-59.bpo-40105.hfM2c0.rst Normal file
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@ -0,0 +1,2 @@
ZipFile truncates files to avoid corruption when a shorter comment is provided
in append ("a") mode. Patch by Jan Mazur.