feature #384: Specify custom map key sort function

api_tests/marshal_json_test.go

@@ -4,11 +4,10 @@ import (
 	"bytes"
 	"encoding/json"
 	"github.com/json-iterator/go"
-	"testing"
 	"github.com/stretchr/testify/require"
+	"testing"
 )
 
-
 type Foo struct {
 	Bar interface{}
 }
@@ -19,11 +18,10 @@ func (f Foo) MarshalJSON() ([]byte, error) {
 	return buf.Bytes(), err
 }
 
-
 // Standard Encoder has trailing newline.
 func TestEncodeMarshalJSON(t *testing.T) {
 
-	foo := Foo {
+	foo := Foo{
 		Bar: 123,
 	}
 	should := require.New(t)

extension_tests/extension_test.go

@@ -61,6 +61,79 @@ func Test_customize_map_key_encoder(t *testing.T) {
 	should.Equal(map[int]int{1: 2}, m)
 }
 
+// Test using custom encoder with sorted map keys.
+// Keys should be numerically sorted AFTER the custom key encoder runs.
+func Test_customize_map_key_encoder_with_sorted_keys(t *testing.T) {
+	should := require.New(t)
+	cfg := jsoniter.Config{
+		SortMapKeys: true,
+	}.Froze()
+	cfg.RegisterExtension(&testMapKeyExtension{})
+	m := map[int]int{
+		3: 3,
+		1: 9,
+	}
+	output, err := cfg.MarshalToString(m)
+	should.NoError(err)
+	should.Equal(`{"2":9,"4":3}`, output)
+	m2 := map[int]int{}
+	should.NoError(cfg.UnmarshalFromString(output, &m2))
+	should.Equal(map[int]int{
+		1: 9,
+		3: 3,
+	}, m2)
+}
+
+func Test_customize_map_key_sorter(t *testing.T) {
+	should := require.New(t)
+	cfg := jsoniter.Config{
+		SortMapKeys: true,
+	}.Froze()
+
+	cfg.RegisterExtension(&testMapKeySorterExtension{
+		sorter: &testKeySorter{},
+	})
+
+	m := map[string]int{
+		"a":   1,
+		"foo": 2,
+		"b":   3,
+	}
+	output, err := cfg.MarshalToString(m)
+	should.NoError(err)
+	should.Equal(`{"foo":2,"a":1,"b":3}`, output)
+	m = map[string]int{}
+	should.NoError(cfg.UnmarshalFromString(output, &m))
+	should.Equal(map[string]int{
+		"foo": 2,
+		"a":   1,
+		"b":   3,
+	}, m)
+}
+
+type testKeySorter struct {
+}
+
+func (sorter *testKeySorter) Sort(keyA string, keyB string) bool {
+	// Prioritize "foo" over other keys, otherwise alpha-sort
+	if keyA == "foo" {
+		return true
+	} else if keyB == "foo" {
+		return false
+	} else {
+		return keyA < keyB
+	}
+}
+
+type testMapKeySorterExtension struct {
+	jsoniter.DummyExtension
+	sorter jsoniter.MapKeySorter
+}
+
+func (extension *testMapKeySorterExtension) CreateMapKeySorter() jsoniter.MapKeySorter {
+	return extension.sorter
+}
+
 type testMapKeyExtension struct {
 	jsoniter.DummyExtension
 }

reflect.go

@@ -30,6 +30,11 @@ type ValEncoder interface {
 	Encode(ptr unsafe.Pointer, stream *Stream)
 }
 
+// MapKeySorter is used to define a custom function for sorting the keys of maps
+type MapKeySorter interface {
+	Sort(keyA string, keyB string) bool
+}
+
 type checkIsEmpty interface {
 	IsEmpty(ptr unsafe.Pointer) bool
 }

reflect_extension.go

@@ -49,6 +49,7 @@ type Extension interface {
 	UpdateStructDescriptor(structDescriptor *StructDescriptor)
 	CreateMapKeyDecoder(typ reflect2.Type) ValDecoder
 	CreateMapKeyEncoder(typ reflect2.Type) ValEncoder
+	CreateMapKeySorter() MapKeySorter
 	CreateDecoder(typ reflect2.Type) ValDecoder
 	CreateEncoder(typ reflect2.Type) ValEncoder
 	DecorateDecoder(typ reflect2.Type, decoder ValDecoder) ValDecoder
@@ -73,6 +74,11 @@ func (extension *DummyExtension) CreateMapKeyEncoder(typ reflect2.Type) ValEncod
 	return nil
 }
 
+// CreateMapKeySorter No-op
+func (extension *DummyExtension) CreateMapKeySorter() MapKeySorter {
+	return nil
+}
+
 // CreateDecoder No-op
 func (extension *DummyExtension) CreateDecoder(typ reflect2.Type) ValDecoder {
 	return nil
@@ -119,6 +125,11 @@ func (extension EncoderExtension) CreateMapKeyEncoder(typ reflect2.Type) ValEnco
 	return nil
 }
 
+// CreateMapKeySorter No-op
+func (extension EncoderExtension) CreateMapKeySorter() MapKeySorter {
+	return nil
+}
+
 // DecorateDecoder No-op
 func (extension EncoderExtension) DecorateDecoder(typ reflect2.Type, decoder ValDecoder) ValDecoder {
 	return decoder
@@ -145,6 +156,11 @@ func (extension DecoderExtension) CreateMapKeyEncoder(typ reflect2.Type) ValEnco
 	return nil
 }
 
+// CreateMapKeySorter No-op
+func (extension DecoderExtension) CreateMapKeySorter() MapKeySorter {
+	return nil
+}
+
 // CreateDecoder get decoder from map
 func (extension DecoderExtension) CreateDecoder(typ reflect2.Type) ValDecoder {
 	return extension[typ]

reflect_map.go

@@ -28,6 +28,7 @@ func encoderOfMap(ctx *ctx, typ reflect2.Type) ValEncoder {
 		return &sortKeysMapEncoder{
 			mapType:     mapType,
 			keyEncoder:  encoderOfMapKey(ctx.append("[mapKey]"), mapType.Key()),
+			keySorter:   sorterOfMapKey(ctx),
 			elemEncoder: encoderOfType(ctx.append("[mapElem]"), mapType.Elem()),
 		}
 	}
@@ -38,6 +39,23 @@ func encoderOfMap(ctx *ctx, typ reflect2.Type) ValEncoder {
 	}
 }
 
+type defaultMapKeySorter struct {
+}
+
+func (sorter defaultMapKeySorter) Sort(keyA string, keyB string) bool {
+	return keyA < keyB
+}
+
+func sorterOfMapKey(ctx *ctx) MapKeySorter {
+	for _, extension := range ctx.extraExtensions {
+		sorter := extension.CreateMapKeySorter()
+		if sorter != nil {
+			return sorter
+		}
+	}
+	return defaultMapKeySorter{}
+}
+
 func decoderOfMapKey(ctx *ctx, typ reflect2.Type) ValDecoder {
 	decoder := ctx.decoderExtension.CreateMapKeyDecoder(typ)
 	if decoder != nil {
@@ -275,6 +293,7 @@ func (encoder *mapEncoder) IsEmpty(ptr unsafe.Pointer) bool {
 type sortKeysMapEncoder struct {
 	mapType     *reflect2.UnsafeMapType
 	keyEncoder  ValEncoder
+	keySorter   MapKeySorter
 	elemEncoder ValEncoder
 }
 
@@ -287,7 +306,7 @@ func (encoder *sortKeysMapEncoder) Encode(ptr unsafe.Pointer, stream *Stream) {
 	mapIter := encoder.mapType.UnsafeIterate(ptr)
 	subStream := stream.cfg.BorrowStream(nil)
 	subIter := stream.cfg.BorrowIterator(nil)
-	keyValues := encodedKeyValues{}
+	keyValues := []encodedKV{}
 	for mapIter.HasNext() {
 		subStream.buf = make([]byte, 0, 64)
 		key, elem := mapIter.UnsafeNext()
@@ -309,7 +328,11 @@ func (encoder *sortKeysMapEncoder) Encode(ptr unsafe.Pointer, stream *Stream) {
 			keyValue: subStream.Buffer(),
 		})
 	}
-	sort.Sort(keyValues)
+	keyValueWrapper := encodedKeyValues{
+		keySorter: encoder.keySorter,
+		values:    keyValues,
+	}
+	sort.Sort(keyValueWrapper)
 	for i, keyValue := range keyValues {
 		if i != 0 {
 			stream.WriteMore()
@@ -326,13 +349,18 @@ func (encoder *sortKeysMapEncoder) IsEmpty(ptr unsafe.Pointer) bool {
 	return !iter.HasNext()
 }
 
-type encodedKeyValues []encodedKV
+type encodedKeyValues struct {
+	keySorter MapKeySorter
+	values    []encodedKV
+}
 
 type encodedKV struct {
 	key      string
 	keyValue []byte
 }
 
-func (sv encodedKeyValues) Len() int           { return len(sv) }
+func (sv encodedKeyValues) Len() int      { return len(sv.values) }
-func (sv encodedKeyValues) Swap(i, j int)      { sv[i], sv[j] = sv[j], sv[i] }
+func (sv encodedKeyValues) Swap(i, j int) { sv.values[i], sv.values[j] = sv.values[j], sv.values[i] }
-func (sv encodedKeyValues) Less(i, j int) bool { return sv[i].key < sv[j].key }
+func (sv encodedKeyValues) Less(i, j int) bool {
+	return sv.keySorter.Sort(sv.values[i].key, sv.values[j].key)
+}