Fixed #25938 -- Factored out CPointerBase base class for GEOSBase/GDALBase.

tests/gis_tests/test_ptr.py

@@ -0,0 +1,65 @@
+import ctypes
+
+from django.contrib.gis.ptr import CPointerBase
+from django.test import SimpleTestCase, mock
+
+
+class CPointerBaseTests(SimpleTestCase):
+
+    def test(self):
+        destructor_mock = mock.Mock()
+
+        class NullPointerException(Exception):
+            pass
+
+        class FakeGeom1(CPointerBase):
+            null_ptr_exception_class = NullPointerException
+
+        class FakeGeom2(FakeGeom1):
+            ptr_type = ctypes.POINTER(ctypes.c_float)
+            destructor = destructor_mock
+
+        fg1 = FakeGeom1()
+        fg2 = FakeGeom2()
+
+        # These assignments are OK. None is allowed because it's equivalent
+        # to the NULL pointer.
+        fg1.ptr = fg1.ptr_type()
+        fg1.ptr = None
+        fg2.ptr = fg2.ptr_type(ctypes.c_float(5.23))
+        fg2.ptr = None
+
+        # Because pointers have been set to NULL, an exception is raised on
+        # access. Raising an exception is preferable to a segmentation fault
+        # that commonly occurs when a C method is given a NULL reference.
+        for fg in (fg1, fg2):
+            with self.assertRaises(NullPointerException):
+                fg.ptr
+
+        # Anything that's either not None or the acceptable pointer type
+        # results in a TypeError when trying to assign it to the `ptr` property.
+        # Thus, memory addresses (integers) and pointers of the incorrect type
+        # (in `bad_ptrs`) aren't allowed.
+        bad_ptrs = (5, ctypes.c_char_p(b'foobar'))
+        for bad_ptr in bad_ptrs:
+            for fg in (fg1, fg2):
+                with self.assertRaisesMessage(TypeError, 'Incompatible pointer type'):
+                    fg.ptr = bad_ptr
+
+        # Object can be deleted without a destructor set.
+        fg = FakeGeom1()
+        fg.ptr = fg.ptr_type(1)
+        del fg
+
+        # A NULL pointer isn't passed to the destructor.
+        fg = FakeGeom2()
+        fg.ptr = None
+        del fg
+        self.assertFalse(destructor_mock.called)
+
+        # The destructor is called if set.
+        fg = FakeGeom2()
+        ptr = fg.ptr_type(ctypes.c_float(1.))
+        fg.ptr = ptr
+        del fg
+        destructor_mock.assert_called_with(ptr)