Merge pull request #242 from goccy/feature/improve-decoder-performance

Add DecodeFieldPriorityFirstWin option

benchmarks/decode_test.go

@@ -375,6 +375,34 @@ func Benchmark_Decode_LargeStruct_Unmarshal_GoJsonNoEscape(b *testing.B) {
 	}
 }
 
+func Benchmark_Decode_LargeStruct_Unmarshal_GoJsonFirstWinMode(b *testing.B) {
+	b.ReportAllocs()
+	for i := 0; i < b.N; i++ {
+		result := LargePayload{}
+		if err := gojson.UnmarshalWithOption(
+			LargeFixture,
+			&result,
+			gojson.DecodeFieldPriorityFirstWin(),
+		); err != nil {
+			b.Fatal(err)
+		}
+	}
+}
+
+func Benchmark_Decode_LargeStruct_Unmarshal_GoJsonNoEscapeFirstWinMode(b *testing.B) {
+	b.ReportAllocs()
+	for i := 0; i < b.N; i++ {
+		result := LargePayload{}
+		if err := gojson.UnmarshalNoEscape(
+			LargeFixture,
+			&result,
+			gojson.DecodeFieldPriorityFirstWin(),
+		); err != nil {
+			b.Fatal(err)
+		}
+	}
+}
+
 func Benchmark_Decode_LargeStruct_Stream_EncodingJson(b *testing.B) {
 	b.ReportAllocs()
 	reader := bytes.NewReader(LargeFixture)
@@ -434,3 +462,18 @@ func Benchmark_Decode_LargeStruct_Stream_GoJson(b *testing.B) {
 		}
 	}
 }
+
+func Benchmark_Decode_LargeStruct_Stream_GoJsonFirstWinMode(b *testing.B) {
+	b.ReportAllocs()
+	reader := bytes.NewReader(LargeFixture)
+	for i := 0; i < b.N; i++ {
+		result := LargePayload{}
+		reader.Reset(LargeFixture)
+		if err := gojson.NewDecoder(reader).DecodeWithOption(
+			&result,
+			gojson.DecodeFieldPriorityFirstWin(),
+		); err != nil {
+			b.Fatal(err)
+		}
+	}
+}

decode.go

@@ -24,7 +24,7 @@ type emptyInterface struct {
 	ptr unsafe.Pointer
 }
 
-func unmarshal(data []byte, v interface{}) error {
+func unmarshal(data []byte, v interface{}, optFuncs ...DecodeOptionFunc) error {
 	src := make([]byte, len(data)+1) // append nul byte to the end
 	copy(src, data)
 
@@ -37,14 +37,22 @@ func unmarshal(data []byte, v interface{}) error {
 	if err != nil {
 		return err
 	}
-	cursor, err := dec.Decode(src, 0, 0, header.ptr)
+	ctx := decoder.TakeRuntimeContext()
+	ctx.Buf = src
+	ctx.Option.Flag = 0
+	for _, optFunc := range optFuncs {
+		optFunc(ctx.Option)
+	}
+	cursor, err := dec.Decode(ctx, 0, 0, header.ptr)
 	if err != nil {
+		decoder.ReleaseRuntimeContext(ctx)
 		return err
 	}
+	decoder.ReleaseRuntimeContext(ctx)
 	return validateEndBuf(src, cursor)
 }
 
-func unmarshalNoEscape(data []byte, v interface{}) error {
+func unmarshalNoEscape(data []byte, v interface{}, optFuncs ...DecodeOptionFunc) error {
 	src := make([]byte, len(data)+1) // append nul byte to the end
 	copy(src, data)
 
@@ -57,10 +65,19 @@ func unmarshalNoEscape(data []byte, v interface{}) error {
 	if err != nil {
 		return err
 	}
-	cursor, err := dec.Decode(src, 0, 0, noescape(header.ptr))
+
+	ctx := decoder.TakeRuntimeContext()
+	ctx.Buf = src
+	ctx.Option.Flag = 0
+	for _, optFunc := range optFuncs {
+		optFunc(ctx.Option)
+	}
+	cursor, err := dec.Decode(ctx, 0, 0, noescape(header.ptr))
 	if err != nil {
+		decoder.ReleaseRuntimeContext(ctx)
 		return err
 	}
+	decoder.ReleaseRuntimeContext(ctx)
 	return validateEndBuf(src, cursor)
 }
 
@@ -117,6 +134,10 @@ func (d *Decoder) Buffered() io.Reader {
 // See the documentation for Unmarshal for details about
 // the conversion of JSON into a Go value.
 func (d *Decoder) Decode(v interface{}) error {
+	return d.DecodeWithOption(v)
+}
+
+func (d *Decoder) DecodeWithOption(v interface{}, optFuncs ...DecodeOptionFunc) error {
 	header := (*emptyInterface)(unsafe.Pointer(&v))
 	typ := header.typ
 	ptr := uintptr(header.ptr)
@@ -136,6 +157,9 @@ func (d *Decoder) Decode(v interface{}) error {
 		return err
 	}
 	s := d.s
+	for _, optFunc := range optFuncs {
+		optFunc(s.Option)
+	}
 	if err := dec.DecodeStream(s, 0, header.ptr); err != nil {
 		return err
 	}

internal/decoder/anonymous_field.go

@@ -28,10 +28,10 @@ func (d *anonymousFieldDecoder) DecodeStream(s *Stream, depth int64, p unsafe.Po
 	return d.dec.DecodeStream(s, depth, unsafe.Pointer(uintptr(p)+d.offset))
 }
 
-func (d *anonymousFieldDecoder) Decode(buf []byte, cursor, depth int64, p unsafe.Pointer) (int64, error) {
+func (d *anonymousFieldDecoder) Decode(ctx *RuntimeContext, cursor, depth int64, p unsafe.Pointer) (int64, error) {
 	if *(*unsafe.Pointer)(p) == nil {
 		*(*unsafe.Pointer)(p) = unsafe_New(d.structType)
 	}
 	p = *(*unsafe.Pointer)(p)
-	return d.dec.Decode(buf, cursor, depth, unsafe.Pointer(uintptr(p)+d.offset))
+	return d.dec.Decode(ctx, cursor, depth, unsafe.Pointer(uintptr(p)+d.offset))
 }

internal/decoder/array.go

@@ -58,8 +58,7 @@ func (d *arrayDecoder) DecodeStream(s *Stream, depth int64, p unsafe.Pointer) er
 					}
 				}
 				idx++
-				s.skipWhiteSpace()
+				switch s.skipWhiteSpace() {
-				switch s.char() {
 				case ']':
 					for idx < d.alen {
 						*(*unsafe.Pointer)(unsafe.Pointer(uintptr(p) + uintptr(idx)*d.size)) = d.zeroValue
@@ -92,7 +91,8 @@ ERROR:
 	return errors.ErrUnexpectedEndOfJSON("array", s.totalOffset())
 }
 
-func (d *arrayDecoder) Decode(buf []byte, cursor, depth int64, p unsafe.Pointer) (int64, error) {
+func (d *arrayDecoder) Decode(ctx *RuntimeContext, cursor, depth int64, p unsafe.Pointer) (int64, error) {
+	buf := ctx.Buf
 	depth++
 	if depth > maxDecodeNestingDepth {
 		return 0, errors.ErrExceededMaxDepth(buf[cursor], cursor)
@@ -114,7 +114,7 @@ func (d *arrayDecoder) Decode(buf []byte, cursor, depth int64, p unsafe.Pointer)
 			for {
 				cursor++
 				if idx < d.alen {
-					c, err := d.valueDecoder.Decode(buf, cursor, depth, unsafe.Pointer(uintptr(p)+uintptr(idx)*d.size))
+					c, err := d.valueDecoder.Decode(ctx, cursor, depth, unsafe.Pointer(uintptr(p)+uintptr(idx)*d.size))
 					if err != nil {
 						return 0, err
 					}

internal/decoder/bool.go

@@ -16,9 +16,9 @@ func newBoolDecoder(structName, fieldName string) *boolDecoder {
 }
 
 func (d *boolDecoder) DecodeStream(s *Stream, depth int64, p unsafe.Pointer) error {
-	s.skipWhiteSpace()
+	c := s.skipWhiteSpace()
 	for {
-		switch s.char() {
+		switch c {
 		case 't':
 			if err := trueBytes(s); err != nil {
 				return err
@@ -38,6 +38,7 @@ func (d *boolDecoder) DecodeStream(s *Stream, depth int64, p unsafe.Pointer) err
 			return nil
 		case nul:
 			if s.read() {
+				c = s.char()
 				continue
 			}
 			goto ERROR
@@ -48,7 +49,8 @@ ERROR:
 	return errors.ErrUnexpectedEndOfJSON("bool", s.totalOffset())
 }
 
-func (d *boolDecoder) Decode(buf []byte, cursor, depth int64, p unsafe.Pointer) (int64, error) {
+func (d *boolDecoder) Decode(ctx *RuntimeContext, cursor, depth int64, p unsafe.Pointer) (int64, error) {
+	buf := ctx.Buf
 	cursor = skipWhiteSpace(buf, cursor)
 	switch buf[cursor] {
 	case 't':

internal/decoder/bytes.go

@@ -57,8 +57,8 @@ func (d *bytesDecoder) DecodeStream(s *Stream, depth int64, p unsafe.Pointer) er
 	return nil
 }
 
-func (d *bytesDecoder) Decode(buf []byte, cursor, depth int64, p unsafe.Pointer) (int64, error) {
+func (d *bytesDecoder) Decode(ctx *RuntimeContext, cursor, depth int64, p unsafe.Pointer) (int64, error) {
-	bytes, c, err := d.decodeBinary(buf, cursor, depth, p)
+	bytes, c, err := d.decodeBinary(ctx, cursor, depth, p)
 	if err != nil {
 		return 0, err
 	}
@@ -131,7 +131,8 @@ func (d *bytesDecoder) decodeStreamBinary(s *Stream, depth int64, p unsafe.Point
 	return nil, errors.ErrNotAtBeginningOfValue(s.totalOffset())
 }
 
-func (d *bytesDecoder) decodeBinary(buf []byte, cursor, depth int64, p unsafe.Pointer) ([]byte, int64, error) {
+func (d *bytesDecoder) decodeBinary(ctx *RuntimeContext, cursor, depth int64, p unsafe.Pointer) ([]byte, int64, error) {
+	buf := ctx.Buf
 	for {
 		switch buf[cursor] {
 		case ' ', '\n', '\t', '\r':
@@ -157,7 +158,7 @@ func (d *bytesDecoder) decodeBinary(buf []byte, cursor, depth int64, p unsafe.Po
 					Offset: cursor,
 				}
 			}
-			c, err := d.sliceDecoder.Decode(buf, cursor, depth, p)
+			c, err := d.sliceDecoder.Decode(ctx, cursor, depth, p)
 			if err != nil {
 				return nil, 0, err
 			}

internal/decoder/context.go

@@ -1,11 +1,35 @@
 package decoder
 
 import (
+	"sync"
 	"unsafe"
 
 	"github.com/goccy/go-json/internal/errors"
 )
 
+type RuntimeContext struct {
+	Buf    []byte
+	Option *Option
+}
+
+var (
+	runtimeContextPool = sync.Pool{
+		New: func() interface{} {
+			return &RuntimeContext{
+				Option: &Option{},
+			}
+		},
+	}
+)
+
+func TakeRuntimeContext() *RuntimeContext {
+	return runtimeContextPool.Get().(*RuntimeContext)
+}
+
+func ReleaseRuntimeContext(ctx *RuntimeContext) {
+	runtimeContextPool.Put(ctx)
+}
+
 var (
 	isWhiteSpace = [256]bool{}
 )

internal/decoder/float.go

@@ -135,7 +135,8 @@ func (d *floatDecoder) DecodeStream(s *Stream, depth int64, p unsafe.Pointer) er
 	return nil
 }
 
-func (d *floatDecoder) Decode(buf []byte, cursor, depth int64, p unsafe.Pointer) (int64, error) {
+func (d *floatDecoder) Decode(ctx *RuntimeContext, cursor, depth int64, p unsafe.Pointer) (int64, error) {
+	buf := ctx.Buf
 	bytes, c, err := d.decodeByte(buf, cursor)
 	if err != nil {
 		return 0, err

internal/decoder/int.go

@@ -209,8 +209,8 @@ func (d *intDecoder) DecodeStream(s *Stream, depth int64, p unsafe.Pointer) erro
 	return nil
 }
 
-func (d *intDecoder) Decode(buf []byte, cursor, depth int64, p unsafe.Pointer) (int64, error) {
+func (d *intDecoder) Decode(ctx *RuntimeContext, cursor, depth int64, p unsafe.Pointer) (int64, error) {
-	bytes, c, err := d.decodeByte(buf, cursor)
+	bytes, c, err := d.decodeByte(ctx.Buf, cursor)
 	if err != nil {
 		return 0, err
 	}

internal/decoder/interface.go

@@ -176,9 +176,9 @@ func decodeTextUnmarshaler(buf []byte, cursor, depth int64, unmarshaler encoding
 }
 
 func (d *interfaceDecoder) decodeStreamEmptyInterface(s *Stream, depth int64, p unsafe.Pointer) error {
-	s.skipWhiteSpace()
+	c := s.skipWhiteSpace()
 	for {
-		switch s.char() {
+		switch c {
 		case '{':
 			var v map[string]interface{}
 			ptr := unsafe.Pointer(&v)
@@ -203,7 +203,7 @@ func (d *interfaceDecoder) decodeStreamEmptyInterface(s *Stream, depth int64, p
 			for {
 				switch s.char() {
 				case '\\':
-					if err := decodeEscapeString(s); err != nil {
+					if _, err := decodeEscapeString(s, nil); err != nil {
 						return err
 					}
 				case '"':
@@ -239,6 +239,7 @@ func (d *interfaceDecoder) decodeStreamEmptyInterface(s *Stream, depth int64, p
 			return nil
 		case nul:
 			if s.read() {
+				c = s.char()
 				continue
 			}
 		}
@@ -265,8 +266,7 @@ func (d *interfaceDecoder) DecodeStream(s *Stream, depth int64, p unsafe.Pointer
 		if u, ok := rv.Interface().(encoding.TextUnmarshaler); ok {
 			return decodeStreamTextUnmarshaler(s, depth, u, p)
 		}
-		s.skipWhiteSpace()
+		if s.skipWhiteSpace() == 'n' {
-		if s.char() == 'n' {
 			if err := nullBytes(s); err != nil {
 				return err
 			}
@@ -285,8 +285,7 @@ func (d *interfaceDecoder) DecodeStream(s *Stream, depth int64, p unsafe.Pointer
 	if typ.Kind() == reflect.Ptr && typ.Elem() == d.typ || typ.Kind() != reflect.Ptr {
 		return d.decodeStreamEmptyInterface(s, depth, p)
 	}
-	s.skipWhiteSpace()
+	if s.skipWhiteSpace() == 'n' {
-	if s.char() == 'n' {
 		if err := nullBytes(s); err != nil {
 			return err
 		}
@@ -310,7 +309,8 @@ func (d *interfaceDecoder) errUnmarshalType(typ reflect.Type, offset int64) *err
 	}
 }
 
-func (d *interfaceDecoder) Decode(buf []byte, cursor, depth int64, p unsafe.Pointer) (int64, error) {
+func (d *interfaceDecoder) Decode(ctx *RuntimeContext, cursor, depth int64, p unsafe.Pointer) (int64, error) {
+	buf := ctx.Buf
 	runtimeInterfaceValue := *(*interface{})(unsafe.Pointer(&emptyInterface{
 		typ: d.typ,
 		ptr: p,
@@ -340,10 +340,10 @@ func (d *interfaceDecoder) Decode(buf []byte, cursor, depth int64, p unsafe.Poin
 	typ := ifaceHeader.typ
 	if ifaceHeader.ptr == nil || d.typ == typ || typ == nil {
 		// concrete type is empty interface
-		return d.decodeEmptyInterface(buf, cursor, depth, p)
+		return d.decodeEmptyInterface(ctx, cursor, depth, p)
 	}
 	if typ.Kind() == reflect.Ptr && typ.Elem() == d.typ || typ.Kind() != reflect.Ptr {
-		return d.decodeEmptyInterface(buf, cursor, depth, p)
+		return d.decodeEmptyInterface(ctx, cursor, depth, p)
 	}
 	cursor = skipWhiteSpace(buf, cursor)
 	if buf[cursor] == 'n' {
@@ -358,16 +358,17 @@ func (d *interfaceDecoder) Decode(buf []byte, cursor, depth int64, p unsafe.Poin
 	if err != nil {
 		return 0, err
 	}
-	return decoder.Decode(buf, cursor, depth, ifaceHeader.ptr)
+	return decoder.Decode(ctx, cursor, depth, ifaceHeader.ptr)
 }
 
-func (d *interfaceDecoder) decodeEmptyInterface(buf []byte, cursor, depth int64, p unsafe.Pointer) (int64, error) {
+func (d *interfaceDecoder) decodeEmptyInterface(ctx *RuntimeContext, cursor, depth int64, p unsafe.Pointer) (int64, error) {
+	buf := ctx.Buf
 	cursor = skipWhiteSpace(buf, cursor)
 	switch buf[cursor] {
 	case '{':
 		var v map[string]interface{}
 		ptr := unsafe.Pointer(&v)
-		cursor, err := d.mapDecoder.Decode(buf, cursor, depth, ptr)
+		cursor, err := d.mapDecoder.Decode(ctx, cursor, depth, ptr)
 		if err != nil {
 			return 0, err
 		}
@@ -376,18 +377,18 @@ func (d *interfaceDecoder) decodeEmptyInterface(buf []byte, cursor, depth int64,
 	case '[':
 		var v []interface{}
 		ptr := unsafe.Pointer(&v)
-		cursor, err := d.sliceDecoder.Decode(buf, cursor, depth, ptr)
+		cursor, err := d.sliceDecoder.Decode(ctx, cursor, depth, ptr)
 		if err != nil {
 			return 0, err
 		}
 		**(**interface{})(unsafe.Pointer(&p)) = v
 		return cursor, nil
 	case '-', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
-		return d.floatDecoder.Decode(buf, cursor, depth, p)
+		return d.floatDecoder.Decode(ctx, cursor, depth, p)
 	case '"':
 		var v string
 		ptr := unsafe.Pointer(&v)
-		cursor, err := d.stringDecoder.Decode(buf, cursor, depth, ptr)
+		cursor, err := d.stringDecoder.Decode(ctx, cursor, depth, ptr)
 		if err != nil {
 			return 0, err
 		}

internal/decoder/map.go

@@ -42,8 +42,7 @@ func (d *mapDecoder) DecodeStream(s *Stream, depth int64, p unsafe.Pointer) erro
 		return errors.ErrExceededMaxDepth(s.char(), s.cursor)
 	}
 
-	s.skipWhiteSpace()
+	switch s.skipWhiteSpace() {
-	switch s.char() {
 	case 'n':
 		if err := nullBytes(s); err != nil {
 			return err
@@ -54,7 +53,6 @@ func (d *mapDecoder) DecodeStream(s *Stream, depth int64, p unsafe.Pointer) erro
 	default:
 		return errors.ErrExpected("{ character for map value", s.totalOffset())
 	}
-	s.skipWhiteSpace()
 	mapValue := *(*unsafe.Pointer)(p)
 	if mapValue == nil {
 		mapValue = makemap(d.mapType, 0)
@@ -92,7 +90,8 @@ func (d *mapDecoder) DecodeStream(s *Stream, depth int64, p unsafe.Pointer) erro
 	}
 }
 
-func (d *mapDecoder) Decode(buf []byte, cursor, depth int64, p unsafe.Pointer) (int64, error) {
+func (d *mapDecoder) Decode(ctx *RuntimeContext, cursor, depth int64, p unsafe.Pointer) (int64, error) {
+	buf := ctx.Buf
 	depth++
 	if depth > maxDecodeNestingDepth {
 		return 0, errors.ErrExceededMaxDepth(buf[cursor], cursor)
@@ -128,7 +127,7 @@ func (d *mapDecoder) Decode(buf []byte, cursor, depth int64, p unsafe.Pointer) (
 	}
 	for {
 		k := unsafe_New(d.keyType)
-		keyCursor, err := d.keyDecoder.Decode(buf, cursor, depth, k)
+		keyCursor, err := d.keyDecoder.Decode(ctx, cursor, depth, k)
 		if err != nil {
 			return 0, err
 		}
@@ -138,7 +137,7 @@ func (d *mapDecoder) Decode(buf []byte, cursor, depth int64, p unsafe.Pointer) (
 		}
 		cursor++
 		v := unsafe_New(d.valueType)
-		valueCursor, err := d.valueDecoder.Decode(buf, cursor, depth, v)
+		valueCursor, err := d.valueDecoder.Decode(ctx, cursor, depth, v)
 		if err != nil {
 			return 0, err
 		}

internal/decoder/number.go

@@ -37,8 +37,8 @@ func (d *numberDecoder) DecodeStream(s *Stream, depth int64, p unsafe.Pointer) e
 	return nil
 }
 
-func (d *numberDecoder) Decode(buf []byte, cursor, depth int64, p unsafe.Pointer) (int64, error) {
+func (d *numberDecoder) Decode(ctx *RuntimeContext, cursor, depth int64, p unsafe.Pointer) (int64, error) {
-	bytes, c, err := d.decodeByte(buf, cursor)
+	bytes, c, err := d.decodeByte(ctx.Buf, cursor)
 	if err != nil {
 		return 0, err
 	}

internal/decoder/option.go

@@ -0,0 +1,11 @@
+package decoder
+
+type OptionFlag int
+
+const (
+	FirstWinOption OptionFlag = 1 << iota
+)
+
+type Option struct {
+	Flag OptionFlag
+}

internal/decoder/ptr.go

@@ -35,8 +35,7 @@ func (d *ptrDecoder) contentDecoder() Decoder {
 func unsafe_New(*runtime.Type) unsafe.Pointer
 
 func (d *ptrDecoder) DecodeStream(s *Stream, depth int64, p unsafe.Pointer) error {
-	s.skipWhiteSpace()
+	if s.skipWhiteSpace() == nul {
-	if s.char() == nul {
 		s.read()
 	}
 	if s.char() == 'n' {
@@ -59,7 +58,8 @@ func (d *ptrDecoder) DecodeStream(s *Stream, depth int64, p unsafe.Pointer) erro
 	return nil
 }
 
-func (d *ptrDecoder) Decode(buf []byte, cursor, depth int64, p unsafe.Pointer) (int64, error) {
+func (d *ptrDecoder) Decode(ctx *RuntimeContext, cursor, depth int64, p unsafe.Pointer) (int64, error) {
+	buf := ctx.Buf
 	cursor = skipWhiteSpace(buf, cursor)
 	if buf[cursor] == 'n' {
 		if err := validateNull(buf, cursor); err != nil {
@@ -78,7 +78,7 @@ func (d *ptrDecoder) Decode(buf []byte, cursor, depth int64, p unsafe.Pointer) (
 	} else {
 		newptr = *(*unsafe.Pointer)(p)
 	}
-	c, err := d.dec.Decode(buf, cursor, depth, newptr)
+	c, err := d.dec.Decode(ctx, cursor, depth, newptr)
 	if err != nil {
 		return 0, err
 	}

internal/decoder/slice.go

@@ -111,8 +111,7 @@ func (d *sliceDecoder) DecodeStream(s *Stream, depth int64, p unsafe.Pointer) er
 			return nil
 		case '[':
 			s.cursor++
-			s.skipWhiteSpace()
+			if s.skipWhiteSpace() == ']' {
-			if s.char() == ']' {
 				dst := (*sliceHeader)(p)
 				if dst.data == nil {
 					dst.data = newArray(d.elemType, 0)
@@ -200,7 +199,8 @@ ERROR:
 	return errors.ErrUnexpectedEndOfJSON("slice", s.totalOffset())
 }
 
-func (d *sliceDecoder) Decode(buf []byte, cursor, depth int64, p unsafe.Pointer) (int64, error) {
+func (d *sliceDecoder) Decode(ctx *RuntimeContext, cursor, depth int64, p unsafe.Pointer) (int64, error) {
+	buf := ctx.Buf
 	depth++
 	if depth > maxDecodeNestingDepth {
 		return 0, errors.ErrExceededMaxDepth(buf[cursor], cursor)
@@ -254,7 +254,7 @@ func (d *sliceDecoder) Decode(buf []byte, cursor, depth int64, p unsafe.Pointer)
 						typedmemmove(d.elemType, ep, unsafe_New(d.elemType))
 					}
 				}
-				c, err := d.valueDecoder.Decode(buf, cursor, depth, ep)
+				c, err := d.valueDecoder.Decode(ctx, cursor, depth, ep)
 				if err != nil {
 					return 0, err
 				}

internal/decoder/stream.go

@@ -25,13 +25,15 @@ type Stream struct {
 	allRead               bool
 	UseNumber             bool
 	DisallowUnknownFields bool
+	Option                *Option
 }
 
 func NewStream(r io.Reader) *Stream {
 	return &Stream{
 		r:       r,
 		bufSize: initBufSize,
-		buf:     []byte{nul},
+		buf:     make([]byte, initBufSize),
+		Option:  &Option{},
 	}
 }
 
@@ -90,6 +92,10 @@ func (s *Stream) stat() ([]byte, int64, unsafe.Pointer) {
 	return s.buf, s.cursor, (*sliceHeader)(unsafe.Pointer(&s.buf)).data
 }
 
+func (s *Stream) bufptr() unsafe.Pointer {
+	return (*sliceHeader)(unsafe.Pointer(&s.buf)).data
+}
+
 func (s *Stream) statForRetry() ([]byte, int64, unsafe.Pointer) {
 	s.cursor-- // for retry ( because caller progress cursor position in each loop )
 	return s.buf, s.cursor, (*sliceHeader)(unsafe.Pointer(&s.buf)).data
@@ -194,6 +200,7 @@ func (s *Stream) readBuf() []byte {
 		}
 		remainNotNulCharNum++
 	}
+	s.length = s.cursor + remainNotNulCharNum
 	return s.buf[s.cursor+remainNotNulCharNum:]
 }
 
@@ -205,7 +212,7 @@ func (s *Stream) read() bool {
 	last := len(buf) - 1
 	buf[last] = nul
 	n, err := s.r.Read(buf[:last])
-	s.length = s.cursor + int64(n)
+	s.length += int64(n)
 	if n == last {
 		s.filledBuffer = true
 	} else {
@@ -219,17 +226,21 @@ func (s *Stream) read() bool {
 	return true
 }
 
-func (s *Stream) skipWhiteSpace() {
+func (s *Stream) skipWhiteSpace() byte {
+	p := s.bufptr()
 LOOP:
-	switch s.char() {
+	c := char(p, s.cursor)
+	switch c {
 	case ' ', '\n', '\t', '\r':
 		s.cursor++
 		goto LOOP
 	case nul:
 		if s.read() {
+			p = s.bufptr()
 			goto LOOP
 		}
 	}
+	return c
 }
 
 func (s *Stream) skipObject(depth int64) error {

internal/decoder/string.go

@@ -45,8 +45,8 @@ func (d *stringDecoder) DecodeStream(s *Stream, depth int64, p unsafe.Pointer) e
 	return nil
 }
 
-func (d *stringDecoder) Decode(buf []byte, cursor, depth int64, p unsafe.Pointer) (int64, error) {
+func (d *stringDecoder) Decode(ctx *RuntimeContext, cursor, depth int64, p unsafe.Pointer) (int64, error) {
-	bytes, c, err := d.decodeByte(buf, cursor)
+	bytes, c, err := d.decodeByte(ctx.Buf, cursor)
 	if err != nil {
 		return 0, err
 	}
@@ -93,38 +93,40 @@ func unicodeToRune(code []byte) rune {
 	return r
 }
 
-func decodeUnicodeRune(s *Stream) (rune, int64, error) {
+func decodeUnicodeRune(s *Stream, p unsafe.Pointer) (rune, int64, unsafe.Pointer, error) {
 	const defaultOffset = 5
 	const surrogateOffset = 11
 
 	if s.cursor+defaultOffset >= s.length {
 		if !s.read() {
-			return rune(0), 0, errors.ErrInvalidCharacter(s.char(), "escaped string", s.totalOffset())
+			return rune(0), 0, nil, errors.ErrInvalidCharacter(s.char(), "escaped string", s.totalOffset())
 		}
+		p = s.bufptr()
 	}
 
 	r := unicodeToRune(s.buf[s.cursor+1 : s.cursor+defaultOffset])
 	if utf16.IsSurrogate(r) {
 		if s.cursor+surrogateOffset >= s.length {
 			s.read()
+			p = s.bufptr()
 		}
 		if s.cursor+surrogateOffset >= s.length || s.buf[s.cursor+defaultOffset] != '\\' || s.buf[s.cursor+defaultOffset+1] != 'u' {
-			return unicode.ReplacementChar, defaultOffset, nil
+			return unicode.ReplacementChar, defaultOffset, p, nil
 		}
 		r2 := unicodeToRune(s.buf[s.cursor+defaultOffset+2 : s.cursor+surrogateOffset])
 		if r := utf16.DecodeRune(r, r2); r != unicode.ReplacementChar {
-			return r, surrogateOffset, nil
+			return r, surrogateOffset, p, nil
 		}
 	}
-	return r, defaultOffset, nil
+	return r, defaultOffset, p, nil
 }
 
-func decodeUnicode(s *Stream) error {
+func decodeUnicode(s *Stream, p unsafe.Pointer) (unsafe.Pointer, error) {
 	const backSlashAndULen = 2 // length of \u
 
-	r, offset, err := decodeUnicodeRune(s)
+	r, offset, pp, err := decodeUnicodeRune(s, p)
 	if err != nil {
-		return err
+		return nil, err
 	}
 	unicode := []byte(string(r))
 	unicodeLen := int64(len(unicode))
@@ -132,10 +134,10 @@ func decodeUnicode(s *Stream) error {
 	unicodeOrgLen := offset - 1
 	s.length = s.length - (backSlashAndULen + (unicodeOrgLen - unicodeLen))
 	s.cursor = s.cursor - backSlashAndULen + unicodeLen
-	return nil
+	return pp, nil
 }
 
-func decodeEscapeString(s *Stream) error {
+func decodeEscapeString(s *Stream, p unsafe.Pointer) (unsafe.Pointer, error) {
 	s.cursor++
 RETRY:
 	switch s.buf[s.cursor] {
@@ -156,19 +158,19 @@ RETRY:
 	case 't':
 		s.buf[s.cursor] = '\t'
 	case 'u':
-		return decodeUnicode(s)
+		return decodeUnicode(s, p)
 	case nul:
 		if !s.read() {
-			return errors.ErrInvalidCharacter(s.char(), "escaped string", s.totalOffset())
+			return nil, errors.ErrInvalidCharacter(s.char(), "escaped string", s.totalOffset())
 		}
 		goto RETRY
 	default:
-		return errors.ErrUnexpectedEndOfJSON("string", s.totalOffset())
+		return nil, errors.ErrUnexpectedEndOfJSON("string", s.totalOffset())
 	}
 	s.buf = append(s.buf[:s.cursor-1], s.buf[s.cursor:]...)
 	s.length--
 	s.cursor--
-	return nil
+	return p, nil
 }
 
 var (
@@ -184,9 +186,11 @@ func stringBytes(s *Stream) ([]byte, error) {
 		switch char(p, cursor) {
 		case '\\':
 			s.cursor = cursor
-			if err := decodeEscapeString(s); err != nil {
+			pp, err := decodeEscapeString(s, p)
+			if err != nil {
 				return nil, err
 			}
+			p = pp
 			cursor = s.cursor
 		case '"':
 			literal := s.buf[start:cursor]

internal/decoder/struct.go

@@ -17,6 +17,7 @@ type structFieldSet struct {
 	dec         Decoder
 	offset      uintptr
 	isTaggedKey bool
+	fieldIdx    int
 	key         string
 	keyLen      int64
 	err         error
@@ -24,6 +25,7 @@ type structFieldSet struct {
 
 type structDecoder struct {
 	fieldMap           map[string]*structFieldSet
+	fieldUniqueNameNum int
 	stringDecoder      *stringDecoder
 	structName         string
 	fieldName          string
@@ -66,6 +68,21 @@ const (
 )
 
 func (d *structDecoder) tryOptimize() {
+	fieldUniqueNameMap := map[string]int{}
+	fieldIdx := -1
+	for k, v := range d.fieldMap {
+		lower := strings.ToLower(k)
+		idx, exists := fieldUniqueNameMap[lower]
+		if exists {
+			v.fieldIdx = idx
+		} else {
+			fieldIdx++
+			v.fieldIdx = fieldIdx
+		}
+		fieldUniqueNameMap[lower] = fieldIdx
+	}
+	d.fieldUniqueNameNum = len(fieldUniqueNameMap)
+
 	if d.isTriedOptimize {
 		return
 	}
@@ -627,49 +644,65 @@ func (d *structDecoder) DecodeStream(s *Stream, depth int64, p unsafe.Pointer) e
 		return errors.ErrExceededMaxDepth(s.char(), s.cursor)
 	}
 
-	s.skipWhiteSpace()
+	c := s.skipWhiteSpace()
-	switch s.char() {
+	switch c {
 	case 'n':
 		if err := nullBytes(s); err != nil {
 			return err
 		}
 		return nil
-	case nul:
-		s.read()
 	default:
 		if s.char() != '{' {
 			return errors.ErrNotAtBeginningOfValue(s.totalOffset())
 		}
 	}
 	s.cursor++
-	s.skipWhiteSpace()
+	if s.skipWhiteSpace() == '}' {
-	if s.char() == '}' {
 		s.cursor++
 		return nil
 	}
+	var (
+		seenFields   map[int]struct{}
+		seenFieldNum int
+	)
+	firstWin := (s.Option.Flag & FirstWinOption) != 0
+	if firstWin {
+		seenFields = make(map[int]struct{}, d.fieldUniqueNameNum)
+	}
 	for {
 		s.reset()
 		field, key, err := d.keyStreamDecoder(d, s)
 		if err != nil {
 			return err
 		}
-		s.skipWhiteSpace()
+		if s.skipWhiteSpace() != ':' {
-		if s.char() != ':' {
 			return errors.ErrExpected("colon after object key", s.totalOffset())
 		}
 		s.cursor++
-		if s.char() == nul {
-			if !s.read() {
-				return errors.ErrExpected("object value after colon", s.totalOffset())
-			}
-		}
 		if field != nil {
 			if field.err != nil {
 				return field.err
 			}
+			if firstWin {
+				if _, exists := seenFields[field.fieldIdx]; exists {
+					if err := s.skipValue(depth); err != nil {
+						return err
+					}
+				} else {
 					if err := field.dec.DecodeStream(s, depth, unsafe.Pointer(uintptr(p)+field.offset)); err != nil {
 						return err
 					}
+					seenFieldNum++
+					if d.fieldUniqueNameNum <= seenFieldNum {
+						return s.skipObject(depth)
+					}
+					seenFields[field.fieldIdx] = struct{}{}
+				}
+			} else {
+				if err := field.dec.DecodeStream(s, depth, unsafe.Pointer(uintptr(p)+field.offset)); err != nil {
+					return err
+				}
+			}
 		} else if s.DisallowUnknownFields {
 			return fmt.Errorf("json: unknown field %q", key)
 		} else {
@@ -677,8 +710,7 @@ func (d *structDecoder) DecodeStream(s *Stream, depth int64, p unsafe.Pointer) e
 				return err
 			}
 		}
-		s.skipWhiteSpace()
+		c := s.skipWhiteSpace()
-		c := s.char()
 		if c == '}' {
 			s.cursor++
 			return nil
@@ -690,7 +722,8 @@ func (d *structDecoder) DecodeStream(s *Stream, depth int64, p unsafe.Pointer) e
 	}
 }
 
-func (d *structDecoder) Decode(buf []byte, cursor, depth int64, p unsafe.Pointer) (int64, error) {
+func (d *structDecoder) Decode(ctx *RuntimeContext, cursor, depth int64, p unsafe.Pointer) (int64, error) {
+	buf := ctx.Buf
 	depth++
 	if depth > maxDecodeNestingDepth {
 		return 0, errors.ErrExceededMaxDepth(buf[cursor], cursor)
@@ -715,6 +748,14 @@ func (d *structDecoder) Decode(buf []byte, cursor, depth int64, p unsafe.Pointer
 		cursor++
 		return cursor, nil
 	}
+	var (
+		seenFields   map[int]struct{}
+		seenFieldNum int
+	)
+	firstWin := (ctx.Option.Flag & FirstWinOption) != 0
+	if firstWin {
+		seenFields = make(map[int]struct{}, d.fieldUniqueNameNum)
+	}
 	for {
 		c, field, err := d.keyDecoder(d, buf, cursor)
 		if err != nil {
@@ -732,11 +773,32 @@ func (d *structDecoder) Decode(buf []byte, cursor, depth int64, p unsafe.Pointer
 			if field.err != nil {
 				return 0, field.err
 			}
-			c, err := field.dec.Decode(buf, cursor, depth, unsafe.Pointer(uintptr(p)+field.offset))
+			if firstWin {
+				if _, exists := seenFields[field.fieldIdx]; exists {
+					c, err := skipValue(buf, cursor, depth)
 					if err != nil {
 						return 0, err
 					}
 					cursor = c
+				} else {
+					c, err := field.dec.Decode(ctx, cursor, depth, unsafe.Pointer(uintptr(p)+field.offset))
+					if err != nil {
+						return 0, err
+					}
+					cursor = c
+					seenFieldNum++
+					if d.fieldUniqueNameNum <= seenFieldNum {
+						return skipObject(buf, cursor, depth)
+					}
+					seenFields[field.fieldIdx] = struct{}{}
+				}
+			} else {
+				c, err := field.dec.Decode(ctx, cursor, depth, unsafe.Pointer(uintptr(p)+field.offset))
+				if err != nil {
+					return 0, err
+				}
+				cursor = c
+			}
 		} else {
 			c, err := skipValue(buf, cursor, depth)
 			if err != nil {

internal/decoder/type.go

@@ -8,7 +8,7 @@ import (
 )
 
 type Decoder interface {
-	Decode([]byte, int64, int64, unsafe.Pointer) (int64, error)
+	Decode(*RuntimeContext, int64, int64, unsafe.Pointer) (int64, error)
 	DecodeStream(*Stream, int64, unsafe.Pointer) error
 }
 

internal/decoder/uint.go

@@ -158,8 +158,8 @@ func (d *uintDecoder) DecodeStream(s *Stream, depth int64, p unsafe.Pointer) err
 	return nil
 }
 
-func (d *uintDecoder) Decode(buf []byte, cursor, depth int64, p unsafe.Pointer) (int64, error) {
+func (d *uintDecoder) Decode(ctx *RuntimeContext, cursor, depth int64, p unsafe.Pointer) (int64, error) {
-	bytes, c, err := d.decodeByte(buf, cursor)
+	bytes, c, err := d.decodeByte(ctx.Buf, cursor)
 	if err != nil {
 		return 0, err
 	}

internal/decoder/unmarshal_json.go

@@ -53,7 +53,8 @@ func (d *unmarshalJSONDecoder) DecodeStream(s *Stream, depth int64, p unsafe.Poi
 	return nil
 }
 
-func (d *unmarshalJSONDecoder) Decode(buf []byte, cursor, depth int64, p unsafe.Pointer) (int64, error) {
+func (d *unmarshalJSONDecoder) Decode(ctx *RuntimeContext, cursor, depth int64, p unsafe.Pointer) (int64, error) {
+	buf := ctx.Buf
 	cursor = skipWhiteSpace(buf, cursor)
 	start := cursor
 	end, err := skipValue(buf, cursor, depth)

internal/decoder/unmarshal_text.go

@@ -91,7 +91,8 @@ func (d *unmarshalTextDecoder) DecodeStream(s *Stream, depth int64, p unsafe.Poi
 	return nil
 }
 
-func (d *unmarshalTextDecoder) Decode(buf []byte, cursor, depth int64, p unsafe.Pointer) (int64, error) {
+func (d *unmarshalTextDecoder) Decode(ctx *RuntimeContext, cursor, depth int64, p unsafe.Pointer) (int64, error) {
+	buf := ctx.Buf
 	cursor = skipWhiteSpace(buf, cursor)
 	start := cursor
 	end, err := skipValue(buf, cursor, depth)

internal/decoder/wrapped_string.go

@@ -40,14 +40,14 @@ func (d *wrappedStringDecoder) DecodeStream(s *Stream, depth int64, p unsafe.Poi
 	}
 	b := make([]byte, len(bytes)+1)
 	copy(b, bytes)
-	if _, err := d.dec.Decode(b, 0, depth, p); err != nil {
+	if _, err := d.dec.Decode(&RuntimeContext{Buf: b}, 0, depth, p); err != nil {
 		return err
 	}
 	return nil
 }
 
-func (d *wrappedStringDecoder) Decode(buf []byte, cursor, depth int64, p unsafe.Pointer) (int64, error) {
+func (d *wrappedStringDecoder) Decode(ctx *RuntimeContext, cursor, depth int64, p unsafe.Pointer) (int64, error) {
-	bytes, c, err := d.stringDecoder.decodeByte(buf, cursor)
+	bytes, c, err := d.stringDecoder.decodeByte(ctx.Buf, cursor)
 	if err != nil {
 		return 0, err
 	}
@@ -58,8 +58,11 @@ func (d *wrappedStringDecoder) Decode(buf []byte, cursor, depth int64, p unsafe.
 		return c, nil
 	}
 	bytes = append(bytes, nul)
-	if _, err := d.dec.Decode(bytes, 0, depth, p); err != nil {
+	oldBuf := ctx.Buf
+	ctx.Buf = bytes
+	if _, err := d.dec.Decode(ctx, 0, depth, p); err != nil {
 		return 0, err
 	}
+	ctx.Buf = oldBuf
 	return c, nil
 }

json.go

@@ -258,8 +258,12 @@ func Unmarshal(data []byte, v interface{}) error {
 	return unmarshal(data, v)
 }
 
-func UnmarshalNoEscape(data []byte, v interface{}) error {
+func UnmarshalWithOption(data []byte, v interface{}, optFuncs ...DecodeOptionFunc) error {
-	return unmarshalNoEscape(data, v)
+	return unmarshal(data, v, optFuncs...)
+}
+
+func UnmarshalNoEscape(data []byte, v interface{}, optFuncs ...DecodeOptionFunc) error {
+	return unmarshalNoEscape(data, v, optFuncs...)
 }
 
 // A Token holds a value of one of these types:

option.go

@@ -1,28 +1,46 @@
 package json
 
 import (
+	"github.com/goccy/go-json/internal/decoder"
 	"github.com/goccy/go-json/internal/encoder"
 )
 
 type EncodeOption = encoder.Option
-
 type EncodeOptionFunc func(*EncodeOption)
 
+// UnorderedMap doesn't sort when encoding map type.
 func UnorderedMap() EncodeOptionFunc {
 	return func(opt *EncodeOption) {
 		opt.Flag |= encoder.UnorderedMapOption
 	}
 }
 
+// Debug outputs debug information when panic occurs during encoding.
 func Debug() EncodeOptionFunc {
 	return func(opt *EncodeOption) {
 		opt.Flag |= encoder.DebugOption
 	}
 }
 
+// Colorize add an identifier for coloring to the string of the encoded result.
 func Colorize(scheme *ColorScheme) EncodeOptionFunc {
 	return func(opt *EncodeOption) {
 		opt.Flag |= encoder.ColorizeOption
 		opt.ColorScheme = scheme
 	}
 }
+
+type DecodeOption = decoder.Option
+type DecodeOptionFunc func(*DecodeOption)
+
+// DecodeFieldPriorityFirstWin
+// in the default behavior, go-json, like encoding/json,
+// will reflect the result of the last evaluation when a field with the same name exists.
+// This option allow you to change this behavior.
+// this option reflects the result of the first evaluation if a field with the same name exists.
+// This behavior has a performance advantage as it allows the subsequent strings to be skipped if all fields have been evaluated.
+func DecodeFieldPriorityFirstWin() DecodeOptionFunc {
+	return func(opt *DecodeOption) {
+		opt.Flag |= decoder.FirstWinOption
+	}
+}