Drop unrecognized fields before update

Add a nested store to the proxy store to strip non-Kubernetes fields
from the object being updated.

The steve formatter and proxy store adds fields to objects when it
outputs them to the client, for usability by the UI. It adds the
object's fields[1], relationships to other objects[2], a summary of the
object's state[3], and additional information in the conditions[4].
These fields are not native to Kubernetes, so when a client submits the
object back as an update, Kubernetes reports a warning that they are
unrecognized. This change ensures the extra fields are removed before
submitting the update.

[1] bf2e9655f5/pkg/stores/proxy/proxy_store.go (L189)
[2] bf2e9655f5/pkg/resources/common/formatter.go (L106)
[3] bf2e9655f5/pkg/resources/common/formatter.go (L100)
[4] bf2e9655f5/pkg/resources/common/formatter.go (L108)

pkg/stores/proxy/unformatter_test.go

@@ -0,0 +1,112 @@
+package proxy
+
+import (
+	"testing"
+
+	"github.com/rancher/apiserver/pkg/types"
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_unformat(t *testing.T) {
+	tests := []struct {
+		name string
+		obj  types.APIObject
+		want types.APIObject
+	}{
+		{
+			name: "noop",
+			obj: types.APIObject{
+				Object: map[string]interface{}{
+					"metadata": map[string]interface{}{
+						"name": "noop",
+					},
+				},
+			},
+			want: types.APIObject{
+				Object: map[string]interface{}{
+					"metadata": map[string]interface{}{
+						"name": "noop",
+					},
+				},
+			},
+		},
+		{
+			name: "remove fields",
+			obj: types.APIObject{
+				Object: map[string]interface{}{
+					"metadata": map[string]interface{}{
+						"name": "foo",
+						"fields": []string{
+							"name",
+							"address",
+							"phonenumber",
+						},
+						"relationships": []map[string]interface{}{
+							{
+								"toId": "bar",
+								"rel":  "uses",
+							},
+						},
+						"state": map[string]interface{}{
+							"error": false,
+						},
+					},
+					"status": map[string]interface{}{
+						"conditions": []map[string]interface{}{
+							{
+								"type":           "Ready",
+								"status":         "True",
+								"lastUpdateTime": "a minute ago",
+								"transitioning":  false,
+								"error":          false,
+							},
+							{
+								"type":           "Initialized",
+								"status":         "True",
+								"lastUpdateTime": "yesterday",
+								"transitioning":  false,
+								"error":          false,
+							},
+						},
+					},
+				},
+			},
+			want: types.APIObject{
+				Object: map[string]interface{}{
+					"metadata": map[string]interface{}{
+						"name": "foo",
+					},
+					"status": map[string]interface{}{
+						"conditions": []map[string]interface{}{
+							{
+								"type":   "Ready",
+								"status": "True",
+							},
+							{
+								"type":   "Initialized",
+								"status": "True",
+							},
+						},
+					},
+				},
+			},
+		},
+		{
+			name: "unrecognized object",
+			obj: types.APIObject{
+				Object: "object",
+			},
+			want: types.APIObject{
+				Object: "object",
+			},
+		},
+	}
+	for _, test := range tests {
+		test := test
+		t.Run(test.name, func(t *testing.T) {
+			t.Parallel()
+			got := unformat(test.obj)
+			assert.Equal(t, test.want, got)
+		})
+	}
+}