Benchmark for k8s services (#2107)

* Benchmark for k8s services

* Adding k8s.io/client-go/kubernetes/fake dep

vendor/k8s.io/apimachinery/pkg/util/mergepatch/OWNERS

@@ -0,0 +1,5 @@
+approvers:
+- pwittrock
+reviewers:
+- mengqiy
+- apelisse

vendor/k8s.io/apimachinery/pkg/util/mergepatch/errors.go

@@ -0,0 +1,102 @@
+/*
+Copyright 2017 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package mergepatch
+
+import (
+	"errors"
+	"fmt"
+	"reflect"
+)
+
+var (
+	ErrBadJSONDoc                           = errors.New("invalid JSON document")
+	ErrNoListOfLists                        = errors.New("lists of lists are not supported")
+	ErrBadPatchFormatForPrimitiveList       = errors.New("invalid patch format of primitive list")
+	ErrBadPatchFormatForRetainKeys          = errors.New("invalid patch format of retainKeys")
+	ErrBadPatchFormatForSetElementOrderList = errors.New("invalid patch format of setElementOrder list")
+	ErrPatchContentNotMatchRetainKeys       = errors.New("patch content doesn't match retainKeys list")
+	ErrUnsupportedStrategicMergePatchFormat = errors.New("strategic merge patch format is not supported")
+)
+
+func ErrNoMergeKey(m map[string]interface{}, k string) error {
+	return fmt.Errorf("map: %v does not contain declared merge key: %s", m, k)
+}
+
+func ErrBadArgType(expected, actual interface{}) error {
+	return fmt.Errorf("expected a %s, but received a %s",
+		reflect.TypeOf(expected),
+		reflect.TypeOf(actual))
+}
+
+func ErrBadArgKind(expected, actual interface{}) error {
+	var expectedKindString, actualKindString string
+	if expected == nil {
+		expectedKindString = "nil"
+	} else {
+		expectedKindString = reflect.TypeOf(expected).Kind().String()
+	}
+	if actual == nil {
+		actualKindString = "nil"
+	} else {
+		actualKindString = reflect.TypeOf(actual).Kind().String()
+	}
+	return fmt.Errorf("expected a %s, but received a %s", expectedKindString, actualKindString)
+}
+
+func ErrBadPatchType(t interface{}, m map[string]interface{}) error {
+	return fmt.Errorf("unknown patch type: %s in map: %v", t, m)
+}
+
+// IsPreconditionFailed returns true if the provided error indicates
+// a precondition failed.
+func IsPreconditionFailed(err error) bool {
+	_, ok := err.(ErrPreconditionFailed)
+	return ok
+}
+
+type ErrPreconditionFailed struct {
+	message string
+}
+
+func NewErrPreconditionFailed(target map[string]interface{}) ErrPreconditionFailed {
+	s := fmt.Sprintf("precondition failed for: %v", target)
+	return ErrPreconditionFailed{s}
+}
+
+func (err ErrPreconditionFailed) Error() string {
+	return err.message
+}
+
+type ErrConflict struct {
+	message string
+}
+
+func NewErrConflict(patch, current string) ErrConflict {
+	s := fmt.Sprintf("patch:\n%s\nconflicts with changes made from original to current:\n%s\n", patch, current)
+	return ErrConflict{s}
+}
+
+func (err ErrConflict) Error() string {
+	return err.message
+}
+
+// IsConflict returns true if the provided error indicates
+// a conflict between the patch and the current configuration.
+func IsConflict(err error) bool {
+	_, ok := err.(ErrConflict)
+	return ok
+}

vendor/k8s.io/apimachinery/pkg/util/mergepatch/util.go

@@ -0,0 +1,133 @@
+/*
+Copyright 2017 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package mergepatch
+
+import (
+	"fmt"
+	"reflect"
+
+	"github.com/davecgh/go-spew/spew"
+	"github.com/ghodss/yaml"
+)
+
+// PreconditionFunc asserts that an incompatible change is not present within a patch.
+type PreconditionFunc func(interface{}) bool
+
+// RequireKeyUnchanged returns a precondition function that fails if the provided key
+// is present in the patch (indicating that its value has changed).
+func RequireKeyUnchanged(key string) PreconditionFunc {
+	return func(patch interface{}) bool {
+		patchMap, ok := patch.(map[string]interface{})
+		if !ok {
+			return true
+		}
+
+		// The presence of key means that its value has been changed, so the test fails.
+		_, ok = patchMap[key]
+		return !ok
+	}
+}
+
+// RequireMetadataKeyUnchanged creates a precondition function that fails
+// if the metadata.key is present in the patch (indicating its value
+// has changed).
+func RequireMetadataKeyUnchanged(key string) PreconditionFunc {
+	return func(patch interface{}) bool {
+		patchMap, ok := patch.(map[string]interface{})
+		if !ok {
+			return true
+		}
+		patchMap1, ok := patchMap["metadata"]
+		if !ok {
+			return true
+		}
+		patchMap2, ok := patchMap1.(map[string]interface{})
+		if !ok {
+			return true
+		}
+		_, ok = patchMap2[key]
+		return !ok
+	}
+}
+
+func ToYAMLOrError(v interface{}) string {
+	y, err := toYAML(v)
+	if err != nil {
+		return err.Error()
+	}
+
+	return y
+}
+
+func toYAML(v interface{}) (string, error) {
+	y, err := yaml.Marshal(v)
+	if err != nil {
+		return "", fmt.Errorf("yaml marshal failed:%v\n%v\n", err, spew.Sdump(v))
+	}
+
+	return string(y), nil
+}
+
+// HasConflicts returns true if the left and right JSON interface objects overlap with
+// different values in any key. All keys are required to be strings. Since patches of the
+// same Type have congruent keys, this is valid for multiple patch types. This method
+// supports JSON merge patch semantics.
+//
+// NOTE: Numbers with different types (e.g. int(0) vs int64(0)) will be detected as conflicts.
+//       Make sure the unmarshaling of left and right are consistent (e.g. use the same library).
+func HasConflicts(left, right interface{}) (bool, error) {
+	switch typedLeft := left.(type) {
+	case map[string]interface{}:
+		switch typedRight := right.(type) {
+		case map[string]interface{}:
+			for key, leftValue := range typedLeft {
+				rightValue, ok := typedRight[key]
+				if !ok {
+					continue
+				}
+				if conflict, err := HasConflicts(leftValue, rightValue); err != nil || conflict {
+					return conflict, err
+				}
+			}
+
+			return false, nil
+		default:
+			return true, nil
+		}
+	case []interface{}:
+		switch typedRight := right.(type) {
+		case []interface{}:
+			if len(typedLeft) != len(typedRight) {
+				return true, nil
+			}
+
+			for i := range typedLeft {
+				if conflict, err := HasConflicts(typedLeft[i], typedRight[i]); err != nil || conflict {
+					return conflict, err
+				}
+			}
+
+			return false, nil
+		default:
+			return true, nil
+		}
+	case string, float64, bool, int, int64, nil:
+		return !reflect.DeepEqual(left, right), nil
+	default:
+		return true, fmt.Errorf("unknown type: %v", reflect.TypeOf(left))
+	}
+}

vendor/k8s.io/apimachinery/pkg/util/mergepatch/util_test.go

@@ -0,0 +1,138 @@
+/*
+Copyright 2017 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package mergepatch
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestHasConflicts(t *testing.T) {
+	testCases := []struct {
+		A   interface{}
+		B   interface{}
+		Ret bool
+	}{
+		{A: "hello", B: "hello", Ret: false},
+		{A: "hello", B: "hell", Ret: true},
+		{A: "hello", B: nil, Ret: true},
+		{A: "hello", B: 1, Ret: true},
+		{A: "hello", B: float64(1.0), Ret: true},
+		{A: "hello", B: false, Ret: true},
+		{A: 1, B: 1, Ret: false},
+		{A: nil, B: nil, Ret: false},
+		{A: false, B: false, Ret: false},
+		{A: float64(3), B: float64(3), Ret: false},
+
+		{A: "hello", B: []interface{}{}, Ret: true},
+		{A: []interface{}{1}, B: []interface{}{}, Ret: true},
+		{A: []interface{}{}, B: []interface{}{}, Ret: false},
+		{A: []interface{}{1}, B: []interface{}{1}, Ret: false},
+		{A: map[string]interface{}{}, B: []interface{}{1}, Ret: true},
+
+		{A: map[string]interface{}{}, B: map[string]interface{}{"a": 1}, Ret: false},
+		{A: map[string]interface{}{"a": 1}, B: map[string]interface{}{"a": 1}, Ret: false},
+		{A: map[string]interface{}{"a": 1}, B: map[string]interface{}{"a": 2}, Ret: true},
+		{A: map[string]interface{}{"a": 1}, B: map[string]interface{}{"b": 2}, Ret: false},
+
+		{
+			A:   map[string]interface{}{"a": []interface{}{1}},
+			B:   map[string]interface{}{"a": []interface{}{1}},
+			Ret: false,
+		},
+		{
+			A:   map[string]interface{}{"a": []interface{}{1}},
+			B:   map[string]interface{}{"a": []interface{}{}},
+			Ret: true,
+		},
+		{
+			A:   map[string]interface{}{"a": []interface{}{1}},
+			B:   map[string]interface{}{"a": 1},
+			Ret: true,
+		},
+
+		// Maps and lists with multiple entries.
+		{
+			A:   map[string]interface{}{"a": 1, "b": 2},
+			B:   map[string]interface{}{"a": 1, "b": 0},
+			Ret: true,
+		},
+		{
+			A:   map[string]interface{}{"a": 1, "b": 2},
+			B:   map[string]interface{}{"a": 1, "b": 2},
+			Ret: false,
+		},
+		{
+			A:   map[string]interface{}{"a": 1, "b": 2},
+			B:   map[string]interface{}{"a": 1, "b": 0, "c": 3},
+			Ret: true,
+		},
+		{
+			A:   map[string]interface{}{"a": 1, "b": 2},
+			B:   map[string]interface{}{"a": 1, "b": 2, "c": 3},
+			Ret: false,
+		},
+		{
+			A:   map[string]interface{}{"a": []interface{}{1, 2}},
+			B:   map[string]interface{}{"a": []interface{}{1, 0}},
+			Ret: true,
+		},
+		{
+			A:   map[string]interface{}{"a": []interface{}{1, 2}},
+			B:   map[string]interface{}{"a": []interface{}{1, 2}},
+			Ret: false,
+		},
+
+		// Numeric types are not interchangeable.
+		// Callers are expected to ensure numeric types are consistent in 'left' and 'right'.
+		{A: int(0), B: int64(0), Ret: true},
+		{A: int(0), B: float64(0), Ret: true},
+		{A: int64(0), B: float64(0), Ret: true},
+		// Other types are not interchangeable.
+		{A: int(0), B: "0", Ret: true},
+		{A: int(0), B: nil, Ret: true},
+		{A: int(0), B: false, Ret: true},
+		{A: "true", B: true, Ret: true},
+		{A: "null", B: nil, Ret: true},
+	}
+
+	for _, testCase := range testCases {
+		testStr := fmt.Sprintf("A = %#v, B = %#v", testCase.A, testCase.B)
+		// Run each test case multiple times if it passes because HasConflicts()
+		// uses map iteration, which returns keys in nondeterministic order.
+		for try := 0; try < 10; try++ {
+			out, err := HasConflicts(testCase.A, testCase.B)
+			if err != nil {
+				t.Errorf("%v: unexpected error: %v", testStr, err)
+				break
+			}
+			if out != testCase.Ret {
+				t.Errorf("%v: expected %t got %t", testStr, testCase.Ret, out)
+				break
+			}
+			out, err = HasConflicts(testCase.B, testCase.A)
+			if err != nil {
+				t.Errorf("%v: unexpected error: %v", testStr, err)
+				break
+			}
+			if out != testCase.Ret {
+				t.Errorf("%v: expected reversed %t got %t", testStr, testCase.Ret, out)
+				break
+			}
+		}
+	}
+}

vendor/k8s.io/apimachinery/pkg/util/strategicpatch/OWNERS

@@ -0,0 +1,5 @@
+approvers:
+- pwittrock
+reviewers:
+- mengqiy
+- apelisse

vendor/k8s.io/apimachinery/pkg/util/strategicpatch/errors.go

@@ -0,0 +1,49 @@
+/*
+Copyright 2017 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package strategicpatch
+
+import (
+	"fmt"
+)
+
+type LookupPatchMetaError struct {
+	Path string
+	Err  error
+}
+
+func (e LookupPatchMetaError) Error() string {
+	return fmt.Sprintf("LookupPatchMetaError(%s): %v", e.Path, e.Err)
+}
+
+type FieldNotFoundError struct {
+	Path  string
+	Field string
+}
+
+func (e FieldNotFoundError) Error() string {
+	return fmt.Sprintf("unable to find api field %q in %s", e.Field, e.Path)
+}
+
+type InvalidTypeError struct {
+	Path     string
+	Expected string
+	Actual   string
+}
+
+func (e InvalidTypeError) Error() string {
+	return fmt.Sprintf("invalid type for %s: got %q, expected %q", e.Path, e.Actual, e.Expected)
+}

vendor/k8s.io/apimachinery/pkg/util/strategicpatch/meta.go

@@ -0,0 +1,194 @@
+/*
+Copyright 2017 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package strategicpatch
+
+import (
+	"errors"
+	"fmt"
+	"reflect"
+
+	"k8s.io/apimachinery/pkg/util/mergepatch"
+	forkedjson "k8s.io/apimachinery/third_party/forked/golang/json"
+	openapi "k8s.io/kube-openapi/pkg/util/proto"
+)
+
+type PatchMeta struct {
+	patchStrategies []string
+	patchMergeKey   string
+}
+
+func (pm PatchMeta) GetPatchStrategies() []string {
+	if pm.patchStrategies == nil {
+		return []string{}
+	}
+	return pm.patchStrategies
+}
+
+func (pm PatchMeta) SetPatchStrategies(ps []string) {
+	pm.patchStrategies = ps
+}
+
+func (pm PatchMeta) GetPatchMergeKey() string {
+	return pm.patchMergeKey
+}
+
+func (pm PatchMeta) SetPatchMergeKey(pmk string) {
+	pm.patchMergeKey = pmk
+}
+
+type LookupPatchMeta interface {
+	// LookupPatchMetadataForStruct gets subschema and the patch metadata (e.g. patch strategy and merge key) for map.
+	LookupPatchMetadataForStruct(key string) (LookupPatchMeta, PatchMeta, error)
+	// LookupPatchMetadataForSlice get subschema and the patch metadata for slice.
+	LookupPatchMetadataForSlice(key string) (LookupPatchMeta, PatchMeta, error)
+	// Get the type name of the field
+	Name() string
+}
+
+type PatchMetaFromStruct struct {
+	T reflect.Type
+}
+
+func NewPatchMetaFromStruct(dataStruct interface{}) (PatchMetaFromStruct, error) {
+	t, err := getTagStructType(dataStruct)
+	return PatchMetaFromStruct{T: t}, err
+}
+
+var _ LookupPatchMeta = PatchMetaFromStruct{}
+
+func (s PatchMetaFromStruct) LookupPatchMetadataForStruct(key string) (LookupPatchMeta, PatchMeta, error) {
+	fieldType, fieldPatchStrategies, fieldPatchMergeKey, err := forkedjson.LookupPatchMetadataForStruct(s.T, key)
+	if err != nil {
+		return nil, PatchMeta{}, err
+	}
+
+	return PatchMetaFromStruct{T: fieldType},
+		PatchMeta{
+			patchStrategies: fieldPatchStrategies,
+			patchMergeKey:   fieldPatchMergeKey,
+		}, nil
+}
+
+func (s PatchMetaFromStruct) LookupPatchMetadataForSlice(key string) (LookupPatchMeta, PatchMeta, error) {
+	subschema, patchMeta, err := s.LookupPatchMetadataForStruct(key)
+	if err != nil {
+		return nil, PatchMeta{}, err
+	}
+	elemPatchMetaFromStruct := subschema.(PatchMetaFromStruct)
+	t := elemPatchMetaFromStruct.T
+
+	var elemType reflect.Type
+	switch t.Kind() {
+	// If t is an array or a slice, get the element type.
+	// If element is still an array or a slice, return an error.
+	// Otherwise, return element type.
+	case reflect.Array, reflect.Slice:
+		elemType = t.Elem()
+		if elemType.Kind() == reflect.Array || elemType.Kind() == reflect.Slice {
+			return nil, PatchMeta{}, errors.New("unexpected slice of slice")
+		}
+	// If t is an pointer, get the underlying element.
+	// If the underlying element is neither an array nor a slice, the pointer is pointing to a slice,
+	// e.g. https://github.com/kubernetes/kubernetes/blob/bc22e206c79282487ea0bf5696d5ccec7e839a76/staging/src/k8s.io/apimachinery/pkg/util/strategicpatch/patch_test.go#L2782-L2822
+	// If the underlying element is either an array or a slice, return its element type.
+	case reflect.Ptr:
+		t = t.Elem()
+		if t.Kind() == reflect.Array || t.Kind() == reflect.Slice {
+			t = t.Elem()
+		}
+		elemType = t
+	default:
+		return nil, PatchMeta{}, fmt.Errorf("expected slice or array type, but got: %s", s.T.Kind().String())
+	}
+
+	return PatchMetaFromStruct{T: elemType}, patchMeta, nil
+}
+
+func (s PatchMetaFromStruct) Name() string {
+	return s.T.Kind().String()
+}
+
+func getTagStructType(dataStruct interface{}) (reflect.Type, error) {
+	if dataStruct == nil {
+		return nil, mergepatch.ErrBadArgKind(struct{}{}, nil)
+	}
+
+	t := reflect.TypeOf(dataStruct)
+	// Get the underlying type for pointers
+	if t.Kind() == reflect.Ptr {
+		t = t.Elem()
+	}
+
+	if t.Kind() != reflect.Struct {
+		return nil, mergepatch.ErrBadArgKind(struct{}{}, dataStruct)
+	}
+
+	return t, nil
+}
+
+func GetTagStructTypeOrDie(dataStruct interface{}) reflect.Type {
+	t, err := getTagStructType(dataStruct)
+	if err != nil {
+		panic(err)
+	}
+	return t
+}
+
+type PatchMetaFromOpenAPI struct {
+	Schema openapi.Schema
+}
+
+func NewPatchMetaFromOpenAPI(s openapi.Schema) PatchMetaFromOpenAPI {
+	return PatchMetaFromOpenAPI{Schema: s}
+}
+
+var _ LookupPatchMeta = PatchMetaFromOpenAPI{}
+
+func (s PatchMetaFromOpenAPI) LookupPatchMetadataForStruct(key string) (LookupPatchMeta, PatchMeta, error) {
+	if s.Schema == nil {
+		return nil, PatchMeta{}, nil
+	}
+	kindItem := NewKindItem(key, s.Schema.GetPath())
+	s.Schema.Accept(kindItem)
+
+	err := kindItem.Error()
+	if err != nil {
+		return nil, PatchMeta{}, err
+	}
+	return PatchMetaFromOpenAPI{Schema: kindItem.subschema},
+		kindItem.patchmeta, nil
+}
+
+func (s PatchMetaFromOpenAPI) LookupPatchMetadataForSlice(key string) (LookupPatchMeta, PatchMeta, error) {
+	if s.Schema == nil {
+		return nil, PatchMeta{}, nil
+	}
+	sliceItem := NewSliceItem(key, s.Schema.GetPath())
+	s.Schema.Accept(sliceItem)
+
+	err := sliceItem.Error()
+	if err != nil {
+		return nil, PatchMeta{}, err
+	}
+	return PatchMetaFromOpenAPI{Schema: sliceItem.subschema},
+		sliceItem.patchmeta, nil
+}
+
+func (s PatchMetaFromOpenAPI) Name() string {
+	schema := s.Schema
+	return schema.GetName()
+}

vendor/k8s.io/apimachinery/pkg/util/strategicpatch/types.go

@@ -0,0 +1,193 @@
+/*
+Copyright 2017 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package strategicpatch
+
+import (
+	"errors"
+	"strings"
+
+	"k8s.io/apimachinery/pkg/util/mergepatch"
+	openapi "k8s.io/kube-openapi/pkg/util/proto"
+)
+
+const (
+	patchStrategyOpenapiextensionKey = "x-kubernetes-patch-strategy"
+	patchMergeKeyOpenapiextensionKey = "x-kubernetes-patch-merge-key"
+)
+
+type LookupPatchItem interface {
+	openapi.SchemaVisitor
+
+	Error() error
+	Path() *openapi.Path
+}
+
+type kindItem struct {
+	key          string
+	path         *openapi.Path
+	err          error
+	patchmeta    PatchMeta
+	subschema    openapi.Schema
+	hasVisitKind bool
+}
+
+func NewKindItem(key string, path *openapi.Path) *kindItem {
+	return &kindItem{
+		key:  key,
+		path: path,
+	}
+}
+
+var _ LookupPatchItem = &kindItem{}
+
+func (item *kindItem) Error() error {
+	return item.err
+}
+
+func (item *kindItem) Path() *openapi.Path {
+	return item.path
+}
+
+func (item *kindItem) VisitPrimitive(schema *openapi.Primitive) {
+	item.err = errors.New("expected kind, but got primitive")
+}
+
+func (item *kindItem) VisitArray(schema *openapi.Array) {
+	item.err = errors.New("expected kind, but got slice")
+}
+
+func (item *kindItem) VisitMap(schema *openapi.Map) {
+	item.err = errors.New("expected kind, but got map")
+}
+
+func (item *kindItem) VisitReference(schema openapi.Reference) {
+	if !item.hasVisitKind {
+		schema.SubSchema().Accept(item)
+	}
+}
+
+func (item *kindItem) VisitKind(schema *openapi.Kind) {
+	subschema, ok := schema.Fields[item.key]
+	if !ok {
+		item.err = FieldNotFoundError{Path: schema.GetPath().String(), Field: item.key}
+		return
+	}
+
+	mergeKey, patchStrategies, err := parsePatchMetadata(subschema.GetExtensions())
+	if err != nil {
+		item.err = err
+		return
+	}
+	item.patchmeta = PatchMeta{
+		patchStrategies: patchStrategies,
+		patchMergeKey:   mergeKey,
+	}
+	item.subschema = subschema
+}
+
+type sliceItem struct {
+	key          string
+	path         *openapi.Path
+	err          error
+	patchmeta    PatchMeta
+	subschema    openapi.Schema
+	hasVisitKind bool
+}
+
+func NewSliceItem(key string, path *openapi.Path) *sliceItem {
+	return &sliceItem{
+		key:  key,
+		path: path,
+	}
+}
+
+var _ LookupPatchItem = &sliceItem{}
+
+func (item *sliceItem) Error() error {
+	return item.err
+}
+
+func (item *sliceItem) Path() *openapi.Path {
+	return item.path
+}
+
+func (item *sliceItem) VisitPrimitive(schema *openapi.Primitive) {
+	item.err = errors.New("expected slice, but got primitive")
+}
+
+func (item *sliceItem) VisitArray(schema *openapi.Array) {
+	if !item.hasVisitKind {
+		item.err = errors.New("expected visit kind first, then visit array")
+	}
+	subschema := schema.SubType
+	item.subschema = subschema
+}
+
+func (item *sliceItem) VisitMap(schema *openapi.Map) {
+	item.err = errors.New("expected slice, but got map")
+}
+
+func (item *sliceItem) VisitReference(schema openapi.Reference) {
+	if !item.hasVisitKind {
+		schema.SubSchema().Accept(item)
+	} else {
+		item.subschema = schema.SubSchema()
+	}
+}
+
+func (item *sliceItem) VisitKind(schema *openapi.Kind) {
+	subschema, ok := schema.Fields[item.key]
+	if !ok {
+		item.err = FieldNotFoundError{Path: schema.GetPath().String(), Field: item.key}
+		return
+	}
+
+	mergeKey, patchStrategies, err := parsePatchMetadata(subschema.GetExtensions())
+	if err != nil {
+		item.err = err
+		return
+	}
+	item.patchmeta = PatchMeta{
+		patchStrategies: patchStrategies,
+		patchMergeKey:   mergeKey,
+	}
+	item.hasVisitKind = true
+	subschema.Accept(item)
+}
+
+func parsePatchMetadata(extensions map[string]interface{}) (string, []string, error) {
+	ps, foundPS := extensions[patchStrategyOpenapiextensionKey]
+	var patchStrategies []string
+	var mergeKey, patchStrategy string
+	var ok bool
+	if foundPS {
+		patchStrategy, ok = ps.(string)
+		if ok {
+			patchStrategies = strings.Split(patchStrategy, ",")
+		} else {
+			return "", nil, mergepatch.ErrBadArgType(patchStrategy, ps)
+		}
+	}
+	mk, foundMK := extensions[patchMergeKeyOpenapiextensionKey]
+	if foundMK {
+		mergeKey, ok = mk.(string)
+		if !ok {
+			return "", nil, mergepatch.ErrBadArgType(mergeKey, mk)
+		}
+	}
+	return mergeKey, patchStrategies, nil
+}