Skip empty labels in label creation

This can happen if a Dockerfile contains a LABEL statement without a key value. In this case, we simply ignore the label and don't add it to our table, as it has no defined key.

data/model/oci/label.py

@@ -65,7 +65,7 @@ def create_manifest_label(
 
     # Note that we don't prevent invalid label names coming from the manifest to be stored, as Docker
     # does not currently prevent them from being put into said manifests.
-    if not validate_label_key(key) and source_type_name != "manifest":
+    if source_type_name != "manifest" and not validate_label_key(key):
         raise InvalidLabelKeyException("Key `%s` is invalid or reserved" % key)
 
     # Find the matching media type. If none specified, we infer.

data/model/oci/manifest.py

@@ -310,9 +310,16 @@ def _create_manifest(
             create_temporary_tag_if_necessary(manifest, temp_tag_expiration_sec)
 
     # Define the labels for the manifest (if any).
+    # TODO: Once the old data model is gone, turn this into a batch operation and make the label
+    # application to the manifest occur under the transaction.
     labels = manifest_interface_instance.get_manifest_labels(retriever)
     if labels:
         for key, value in labels.iteritems():
+            # NOTE: There can technically be empty label keys via Dockerfile's. We ignore any
+            # such `labels`, as they don't really mean anything.
+            if not key:
+                continue
+
             media_type = "application/json" if is_json(value) else "text/plain"
             create_manifest_label(manifest, key, value, "manifest", media_type)
 

data/registry_model/registry_pre_oci_model.py

@@ -203,6 +203,11 @@ def create_manifest_and_retarget_tag(
                 for key, value in manifest_interface_instance.layers[
                     -1
                 ].v1_metadata.labels.iteritems():
+                    # NOTE: There can technically be empty label keys via Dockerfile's. We ignore any
+                    # such `labels`, as they don't really mean anything.
+                    if not key:
+                        continue
+
                     media_type = "application/json" if is_json(value) else "text/plain"
                     add_label(key, value, "manifest", media_type)
                     has_labels = True

test/registry/registry_tests.py

@@ -979,6 +979,8 @@ def test_wrong_image_order(legacy_pusher, liveserver_session, app_reloader):
         [("somejson", '{"some": "json"}', "application/json"), ("plain", "", "text/plain")],
         # JSON-esque (but not valid JSON) labels.
         [("foo", "[hello world]", "text/plain"), ("bar", "{wassup?!}", "text/plain")],
+        # Empty key label.
+        [("", "somevalue", "text/plain")],
     ],
 )
 def test_labels(labels, manifest_protocol, liveserver_session, api_caller, app_reloader):
@@ -1004,14 +1006,15 @@ def test_labels(labels, manifest_protocol, liveserver_session, api_caller, app_r
 
     data = api_caller.get("/api/v1/repository/devtable/newrepo/manifest/%s/labels" % digest).json()
     labels_found = data["labels"]
-    assert len(labels_found) == len(labels)
+    assert len(labels_found) == len([label for label in labels if label[0]])
 
     labels_found_map = {l["key"]: l for l in labels_found}
-    assert set(images[0].config["Labels"].keys()) == set(labels_found_map.keys())
+    assert set([k for k in images[0].config["Labels"].keys() if k]) == set(labels_found_map.keys())
 
     for key, _, media_type in labels:
-        assert labels_found_map[key]["source_type"] == "manifest"
-        assert labels_found_map[key]["media_type"] == media_type
+        if key:
+            assert labels_found_map[key]["source_type"] == "manifest"
+            assert labels_found_map[key]["media_type"] == media_type
 
 
 @pytest.mark.parametrize(