k8s.io/kube-openapi@v0.0.0-20240228011516-70dd3763d340/pkg/internal/third_party/go-json-experiment/json/example_orderedobject_test.go

// Copyright 2022 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package json_test

import (
	"fmt"
	"log"
	"reflect"

	"k8s.io/kube-openapi/pkg/internal/third_party/go-json-experiment/json"
)

// OrderedObject is an ordered sequence of name/value members in a JSON object.
//
// RFC 8259 defines an object as an "unordered collection".
// JSON implementations need not make "ordering of object members visible"
// to applications nor will they agree on the semantic meaning of an object if
// "the names within an object are not unique". For maximum compatibility,
// applications should avoid relying on ordering or duplicity of object names.
type OrderedObject[V any] []ObjectMember[V]

// ObjectMember is a JSON object member.
type ObjectMember[V any] struct {
	Name  string
	Value V
}

// MarshalNextJSON encodes obj as a JSON object into enc.
func (obj *OrderedObject[V]) MarshalNextJSON(opts json.MarshalOptions, enc *json.Encoder) error {
	if err := enc.WriteToken(json.ObjectStart); err != nil {
		return err
	}
	for i := range *obj {
		member := &(*obj)[i]
		if err := opts.MarshalNext(enc, &member.Name); err != nil {
			return err
		}
		if err := opts.MarshalNext(enc, &member.Value); err != nil {
			return err
		}
	}
	if err := enc.WriteToken(json.ObjectEnd); err != nil {
		return err
	}
	return nil
}

// UnmarshalNextJSON decodes a JSON object from dec into obj.
func (obj *OrderedObject[V]) UnmarshalNextJSON(opts json.UnmarshalOptions, dec *json.Decoder) error {
	if k := dec.PeekKind(); k != '{' {
		return fmt.Errorf("expected object start, but encountered %v", k)
	}
	if _, err := dec.ReadToken(); err != nil {
		return err
	}
	for dec.PeekKind() != '}' {
		*obj = append(*obj, ObjectMember[V]{})
		member := &(*obj)[len(*obj)-1]
		if err := opts.UnmarshalNext(dec, &member.Name); err != nil {
			return err
		}
		if err := opts.UnmarshalNext(dec, &member.Value); err != nil {
			return err
		}
	}
	if _, err := dec.ReadToken(); err != nil {
		return err
	}
	return nil
}

// The exact order of JSON object can be preserved through the use of a
// specialized type that implements MarshalerV2 and UnmarshalerV2.
func Example_orderedObject() {
	// Round-trip marshal and unmarshal an ordered object.
	// We expect the order and duplicity of JSON object members to be preserved.
	want := OrderedObject[string]{
		{"fizz", "buzz"},
		{"hello", "world"},
		{"fizz", "wuzz"},
	}
	b, err := json.MarshalOptions{}.Marshal(json.EncodeOptions{
		AllowDuplicateNames: true, // since the object contains "fizz" twice
	}, &want)
	if err != nil {
		log.Fatal(err)
	}
	var got OrderedObject[string]
	err = json.UnmarshalOptions{}.Unmarshal(json.DecodeOptions{
		AllowDuplicateNames: true, // since the object contains "fizz" twice
	}, b, &got)
	if err != nil {
		log.Fatal(err)
	}

	// Sanity check.
	if !reflect.DeepEqual(got, want) {
		log.Fatalf("roundtrip mismatch: got %v, want %v", got, want)
	}

	// Print the serialized JSON object.
	(*json.RawValue)(&b).Indent("", "\t") // indent for readability
	fmt.Println(string(b))

	// Output:
	// {
	// 	"fizz": "buzz",
	// 	"hello": "world",
	// 	"fizz": "wuzz"
	// }
}