Make sure SlicedFile is closed properly (#612)

Fixes #556

---------

Co-authored-by: Adam Johnson <me@adamj.eu>

docs/changelog.rst

@@ -11,6 +11,10 @@ Unreleased
 
 * Support Python 3.13.
 
+* Fix a bug introduced in version 6.0.0 where ``Range`` requests could lead to database connection errors in other requests.
+
+  Thanks to Per Myren for the detailed investigation and fix in `PR #612 <https://github.com/evansd/whitenoise/pull/612>`__.
+
 6.7.0 (2024-06-19)
 ------------------
 

src/whitenoise/responders.py

@@ -64,6 +64,7 @@ def read(self, size=-1):
         return data
 
     def close(self):
+        super().close()
         self.fileobj.close()
 
 

tests/test_responders.py

@@ -0,0 +1,42 @@
+from __future__ import annotations
+
+from io import BytesIO
+
+from django.test import SimpleTestCase
+
+from whitenoise.responders import SlicedFile
+
+
+class SlicedFileTests(SimpleTestCase):
+    def test_close_does_not_rerun_on_del(self):
+        """
+        Regression test for the subtle close() behaviour of SlicedFile that
+        could lead to database connection errors.
+
+        https://github.com/evansd/whitenoise/pull/612
+        """
+        file = BytesIO(b"1234567890")
+        sliced_file = SlicedFile(file, 1, 2)
+
+        # Emulate how Django patches the file object's close() method to be
+        # response.close() and count the calls.
+        # https://github.com/django/django/blob/345a6652e6a15febbf4f68351dcea5dd674ea324/django/core/handlers/wsgi.py#L137-L140
+        calls = 0
+
+        file_close = sliced_file.close
+
+        def closer():
+            nonlocal calls, file_close
+            calls += 1
+            if file_close is not None:
+                file_close()
+                file_close = None
+
+        sliced_file.close = closer
+
+        sliced_file.close()
+        assert calls == 1
+
+        # Deleting the sliced file should not call close again.
+        del sliced_file
+        assert calls == 1