Fixed #21033 -- Fixed uploaded filenames not always being truncated to 255 characters

django/core/files/uploadedfile.py

@@ -46,6 +46,7 @@ class UploadedFile(File):
             # File names longer than 255 characters can cause problems on older OSes.
             if len(name) > 255:
                 name, ext = os.path.splitext(name)
+                ext = ext[:255]
                 name = name[:255 - len(ext)] + ext
 
         self._name = name

tests/file_uploads/tests.py

@@ -167,16 +167,26 @@ class FileUploadTests(TestCase):
 
     def test_filename_overflow(self):
         """File names over 256 characters (dangerous on some platforms) get fixed up."""
-        name = "%s.txt" % ("f"*500)
-        payload = client.FakePayload("\r\n".join([
+        long_str = 'f' * 300
+        cases = [
+            # field name, filename, expected
+            ('long_filename', '%s.txt' % long_str, '%s.txt' % long_str[:251]),
+            ('long_extension', 'foo.%s' % long_str, '.%s' % long_str[:254]),
+            ('no_extension', long_str, long_str[:255]),
+            ('no_filename', '.%s' % long_str, '.%s' % long_str[:254]),
+            ('long_everything', '%s.%s' % (long_str, long_str), '.%s' % long_str[:254]),
+        ]
+        payload = client.FakePayload()
+        for name, filename, _ in cases:
+            payload.write("\r\n".join([
                 '--' + client.BOUNDARY,
-            'Content-Disposition: form-data; name="file"; filename="%s"' % name,
+                'Content-Disposition: form-data; name="{0}"; filename="{1}"',
                 'Content-Type: application/octet-stream',
                 '',
-            'Oops.'
-            '--' + client.BOUNDARY + '--',
-            '',
-        ]))
+                'Oops.',
+                ''
+            ]).format(name, filename))
+        payload.write('\r\n--' + client.BOUNDARY + '--\r\n')
         r = {
             'CONTENT_LENGTH': len(payload),
             'CONTENT_TYPE':   client.MULTIPART_CONTENT,
@@ -184,8 +194,12 @@ class FileUploadTests(TestCase):
             'REQUEST_METHOD': 'POST',
             'wsgi.input':     payload,
         }
-        got = json.loads(self.client.request(**r).content.decode('utf-8'))
-        self.assertTrue(len(got['file']) < 256, "Got a long file name (%s characters)." % len(got['file']))
+        result = json.loads(self.client.request(**r).content.decode('utf-8'))
+        for name, _, expected in cases:
+            got = result[name]
+            self.assertEqual(expected, got, 'Mismatch for {0}'.format(name))
+            self.assertTrue(len(got) < 256,
+                            "Got a long file name (%s characters)." % len(got))
 
     def test_content_type_extra(self):
         """Uploaded files may have content type parameters available."""

tests/files/tests.py

@@ -132,7 +132,6 @@ class FileStorageTests(TestCase):
             self.assertEqual(f.read(), b'content')
 
 
-
 class FileTests(unittest.TestCase):
     def test_context_manager(self):
         orig_file = tempfile.TemporaryFile()