example_orderedobject_test.go

Documentation: k8s.io/kube-openapi/pkg/internal/third_party/go-json-experiment/json

     1  // Copyright 2022 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package json_test
     6  
     7  import (
     8  	"fmt"
     9  	"log"
    10  	"reflect"
    11  
    12  	"k8s.io/kube-openapi/pkg/internal/third_party/go-json-experiment/json"
    13  )
    14  
    15  // OrderedObject is an ordered sequence of name/value members in a JSON object.
    16  //
    17  // RFC 8259 defines an object as an "unordered collection".
    18  // JSON implementations need not make "ordering of object members visible"
    19  // to applications nor will they agree on the semantic meaning of an object if
    20  // "the names within an object are not unique". For maximum compatibility,
    21  // applications should avoid relying on ordering or duplicity of object names.
    22  type OrderedObject[V any] []ObjectMember[V]
    23  
    24  // ObjectMember is a JSON object member.
    25  type ObjectMember[V any] struct {
    26  	Name  string
    27  	Value V
    28  }
    29  
    30  // MarshalNextJSON encodes obj as a JSON object into enc.
    31  func (obj *OrderedObject[V]) MarshalNextJSON(opts json.MarshalOptions, enc *json.Encoder) error {
    32  	if err := enc.WriteToken(json.ObjectStart); err != nil {
    33  		return err
    34  	}
    35  	for i := range *obj {
    36  		member := &(*obj)[i]
    37  		if err := opts.MarshalNext(enc, &member.Name); err != nil {
    38  			return err
    39  		}
    40  		if err := opts.MarshalNext(enc, &member.Value); err != nil {
    41  			return err
    42  		}
    43  	}
    44  	if err := enc.WriteToken(json.ObjectEnd); err != nil {
    45  		return err
    46  	}
    47  	return nil
    48  }
    49  
    50  // UnmarshalNextJSON decodes a JSON object from dec into obj.
    51  func (obj *OrderedObject[V]) UnmarshalNextJSON(opts json.UnmarshalOptions, dec *json.Decoder) error {
    52  	if k := dec.PeekKind(); k != '{' {
    53  		return fmt.Errorf("expected object start, but encountered %v", k)
    54  	}
    55  	if _, err := dec.ReadToken(); err != nil {
    56  		return err
    57  	}
    58  	for dec.PeekKind() != '}' {
    59  		*obj = append(*obj, ObjectMember[V]{})
    60  		member := &(*obj)[len(*obj)-1]
    61  		if err := opts.UnmarshalNext(dec, &member.Name); err != nil {
    62  			return err
    63  		}
    64  		if err := opts.UnmarshalNext(dec, &member.Value); err != nil {
    65  			return err
    66  		}
    67  	}
    68  	if _, err := dec.ReadToken(); err != nil {
    69  		return err
    70  	}
    71  	return nil
    72  }
    73  
    74  // The exact order of JSON object can be preserved through the use of a
    75  // specialized type that implements MarshalerV2 and UnmarshalerV2.
    76  func Example_orderedObject() {
    77  	// Round-trip marshal and unmarshal an ordered object.
    78  	// We expect the order and duplicity of JSON object members to be preserved.
    79  	want := OrderedObject[string]{
    80  		{"fizz", "buzz"},
    81  		{"hello", "world"},
    82  		{"fizz", "wuzz"},
    83  	}
    84  	b, err := json.MarshalOptions{}.Marshal(json.EncodeOptions{
    85  		AllowDuplicateNames: true, // since the object contains "fizz" twice
    86  	}, &want)
    87  	if err != nil {
    88  		log.Fatal(err)
    89  	}
    90  	var got OrderedObject[string]
    91  	err = json.UnmarshalOptions{}.Unmarshal(json.DecodeOptions{
    92  		AllowDuplicateNames: true, // since the object contains "fizz" twice
    93  	}, b, &got)
    94  	if err != nil {
    95  		log.Fatal(err)
    96  	}
    97  
    98  	// Sanity check.
    99  	if !reflect.DeepEqual(got, want) {
   100  		log.Fatalf("roundtrip mismatch: got %v, want %v", got, want)
   101  	}
   102  
   103  	// Print the serialized JSON object.
   104  	(*json.RawValue)(&b).Indent("", "\t") // indent for readability
   105  	fmt.Println(string(b))
   106  
   107  	// Output:
   108  	// {
   109  	// 	"fizz": "buzz",
   110  	// 	"hello": "world",
   111  	// 	"fizz": "wuzz"
   112  	// }
   113  }
   114
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