bpo-30980: Fix double close in asyncore.file_wrapper (#2789) (#2898)

* bpo-30980: Fix close test to fail test_close_twice was not considering the fact that file_wrapper is duping the file descriptor. Closing the original descriptor left the duped one open, hiding the fact that close protection is not effective. * bpo-30980: Fix double close protection Invalidated self.fd before closing, handling correctly the case when os.close raises. * bpo-30980: Fix fd leak introduced in the fixed test

Author: nirs

Lib/asyncore.py

@@ -619,8 +619,9 @@ def getsockopt(self, level, optname, buflen=None):
  def close(self):
  if self.fd < 0:
  return
- os.close(self.fd)
+ fd = self.fd
  self.fd = -1
+ os.close(fd)
 
  def fileno(self):
  return self.fd

Lib/test/test_asyncore.py

@@ -433,7 +433,10 @@ def test_close_twice(self):
  f = asyncore.file_wrapper(fd)
  os.close(fd)
 
- f.close()
+ os.close(f.fd) # file_wrapper dupped fd
+ with self.assertRaises(OSError):
+ f.close()
+
  self.assertEqual(f.fd, -1)
  # calling close twice should not fail
  f.close()