py3: Fix status comparison in ECGetResponseCollection

The initial dummy bad bucket was previously stored using None as a
key. In some circumstances this None key might be compared with
integer response status, which is unsupported in py3.

Move away from having any sort of default value and instead return a
default dummy bucket if we don't have any responses or only have 404
responses.

Co-Authored-By: Alistair Coles <alistairncoles@gmail.com>
Change-Id: I6a2ec3739ac92affb0f3dac248f26a1fc4ac9493
Closes-Bug: #1900770

swift/proxy/controllers/obj.py

@@ -2125,7 +2125,8 @@ class ECGetResponseCollection(object):
         """
         self.policy = policy
         self.buckets = {}
-        self.bad_buckets = {None: ECGetResponseBucket(self.policy, None)}
+        self.default_bad_bucket = ECGetResponseBucket(self.policy, None)
+        self.bad_buckets = {}
         self.node_iter_count = 0
 
     def _get_bucket(self, timestamp):
@@ -2254,6 +2255,9 @@ class ECGetResponseCollection(object):
         """
         Return the bad_bucket with the smallest shortfall
         """
+        if all(status == 404 for status in self.bad_buckets):
+            # NB: also covers an empty self.bad_buckets
+            return self.default_bad_bucket
         # we want "enough" 416s to prevent "extra" requests - but we keep
         # digging on 404s
         short, status = min((bucket.shortfall, status)

test/unit/proxy/controllers/test_obj.py

@@ -4003,6 +4003,33 @@ class TestECObjController(ECObjectControllerMixin, unittest.TestCase):
         self.assertEqual(resp.status_int, 416)
         self.assertEqual(len(log), 2 * self.replicas())
 
+    @patch_policies(
+        [ECStoragePolicy(0, name='ec', is_default=True,
+                         ec_type=DEFAULT_TEST_EC_TYPE, ec_ndata=4,
+                         ec_nparity=4, ec_segment_size=4096)],
+        fake_ring_args=[{'replicas': 8}]
+    )
+    def test_GET_ndata_equals_nparity_with_missing_and_errors(self):
+        # when ec_ndata == ec_nparity it is possible for the shortfall of a bad
+        # bucket (412's) to equal ec_ndata; verify that the 412 bucket is still
+        # chosen ahead of the initial 'dummy' bad bucket
+        POLICIES.default.object_ring.max_more_nodes = 8
+        responses = [
+            StubResponse(412, frag_index=0),
+            StubResponse(412, frag_index=1),
+        ]
+
+        def get_response(req):
+            return responses.pop(0) if responses else StubResponse(404)
+
+        req = swob.Request.blank('/v1/a/c/o', headers={
+            'Range': 'bytes=%s-' % 100000000000000})
+        with capture_http_requests(get_response) as log:
+            resp = req.get_response(self.app)
+
+        self.assertEqual(resp.status_int, 412)
+        self.assertEqual(len(log), 2 * 8)
+
     def test_GET_with_success_and_507_will_503(self):
         responses = [  # only 9 good nodes
             StubResponse(200),