bpo-40105: ZipFile truncate in append mode with shorter comment (GH-19337)
diff --git a/Lib/test/test_zipfile.py b/Lib/test/test_zipfile.py
index 2851051..687e43d 100644
--- a/Lib/test/test_zipfile.py
+++ b/Lib/test/test_zipfile.py
@@ -1856,11 +1856,14 @@
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 915698f..816f858 100644
--- a/Lib/zipfile.py
+++ b/Lib/zipfile.py
@@ -1918,6 +1918,8 @@
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):