Issue #28449: tarfile.open() with mode "r" or "r:" now tries to open a tar

file with compression before trying to open it without compression.  Otherwise
it had 50% chance failed with ignore_zeros=True.

Lib/test/test_tarfile.py

@@ -3,6 +3,7 @@ import os
 import io
 from hashlib import md5
 from contextlib import contextmanager
+from random import Random
 
 import unittest
 import unittest.mock
@@ -349,12 +350,17 @@ class CommonReadTest(ReadTest):
 
     def test_ignore_zeros(self):
         # Test TarFile's ignore_zeros option.
+        # generate 512 pseudorandom bytes
+        data = Random(0).getrandbits(512*8).to_bytes(512, 'big')
         for char in (b'\0', b'a'):
             # Test if EOFHeaderError ('\0') and InvalidHeaderError ('a')
             # are ignored correctly.
             with self.open(tmpname, "w") as fobj:
                 fobj.write(char * 1024)
-                fobj.write(tarfile.TarInfo("foo").tobuf())
+                tarinfo = tarfile.TarInfo("foo")
+                tarinfo.size = len(data)
+                fobj.write(tarinfo.tobuf())
+                fobj.write(data)
 
             tar = tarfile.open(tmpname, mode="r", ignore_zeros=True)
             try: