Fixed #23397 -- Stripped whitespace from base64 during chunking

This insures the actual base64 content has a length a multiple of 4.
Also added a test case for the failure.

django/http/multipartparser.py

@@ -206,14 +206,19 @@ class MultiPartParser(object):
                         for chunk in field_stream:
                             if transfer_encoding == 'base64':
                                 # We only special-case base64 transfer encoding
-                                # We should always read base64 streams by multiple of 4
-                                over_bytes = len(chunk) % 4
-                                if over_bytes:
-                                    over_chunk = field_stream.read(4 - over_bytes)
-                                    chunk += over_chunk
+                                # We should always decode base64 chunks by multiple of 4,
+                                # ignoring whitespace.
+
+                                stripped_chunk = b"".join(chunk.split())
+
+                                remaining = len(stripped_chunk) % 4
+                                while remaining != 0:
+                                    over_chunk = field_stream.read(4 - remaining)
+                                    stripped_chunk += b"".join(over_chunk.split())
+                                    remaining = len(stripped_chunk) % 4
 
                                 try:
-                                    chunk = base64.b64decode(chunk)
+                                    chunk = base64.b64decode(stripped_chunk)
                                 except Exception as e:
                                     # Since this is only a chunk, any error is an unfixable error.
                                     msg = "Could not decode base64 data: %r" % e

tests/file_uploads/tests.py

@@ -77,14 +77,14 @@ class FileUploadTests(TestCase):
 
             self.assertEqual(response.status_code, 200)
 
-    def _test_base64_upload(self, content):
+    def _test_base64_upload(self, content, encode=base64.b64encode):
         payload = client.FakePayload("\r\n".join([
             '--' + client.BOUNDARY,
             'Content-Disposition: form-data; name="file"; filename="test.txt"',
             'Content-Type: application/octet-stream',
             'Content-Transfer-Encoding: base64',
             '']))
-        payload.write(b"\r\n" + base64.b64encode(force_bytes(content)) + b"\r\n")
+        payload.write(b"\r\n" + encode(force_bytes(content)) + b"\r\n")
         payload.write('--' + client.BOUNDARY + '--\r\n')
         r = {
             'CONTENT_LENGTH': len(payload),
@@ -104,6 +104,10 @@ class FileUploadTests(TestCase):
     def test_big_base64_upload(self):
         self._test_base64_upload("Big data" * 68000)  # > 512Kb
 
+    def test_big_base64_newlines_upload(self):
+        self._test_base64_upload(
+            "Big data" * 68000, encode=base64.encodestring)
+
     def test_unicode_file_name(self):
         tdir = sys_tempfile.mkdtemp()
         self.addCleanup(shutil.rmtree, tdir, True)