Support DisallowUnknownFields

decode.go

@@ -18,10 +18,12 @@ func (d Delim) String() string {
 type decoder interface {
 	decode([]byte, int64, uintptr) (int64, error)
 	decodeStream(*stream, uintptr) error
+	setDisallowUnknownFields(bool)
 }
 
 type Decoder struct {
-	s *stream
+	s                     *stream
+	disallowUnknownFields bool
 }
 
 type decoderMap struct {
@@ -97,6 +99,7 @@ func (d *Decoder) decode(src []byte, header *interfaceHeader) error {
 		cachedDecoder.set(typeptr, compiledDec)
 		dec = compiledDec
 	}
+	dec.setDisallowUnknownFields(d.disallowUnknownFields)
 	if _, err := dec.decode(src, 0, ptr); err != nil {
 		return err
 	}
@@ -161,6 +164,7 @@ func (d *Decoder) Decode(v interface{}) error {
 		cachedDecoder.set(typeptr, compiledDec)
 		dec = compiledDec
 	}
+	dec.setDisallowUnknownFields(d.disallowUnknownFields)
 	if err := d.prepareForDecode(); err != nil {
 		return err
 	}
@@ -248,7 +252,7 @@ func (d *Decoder) Token() (Token, error) {
 // is a struct and the input contains object keys which do not match any
 // non-ignored, exported fields in the destination.
 func (d *Decoder) DisallowUnknownFields() {
-
+	d.disallowUnknownFields = true
 }
 
 func (d *Decoder) InputOffset() int64 {

decode_array.go

@@ -16,6 +16,10 @@ func newArrayDecoder(dec decoder, elemType *rtype, alen int) *arrayDecoder {
 	}
 }
 
+func (d *arrayDecoder) setDisallowUnknownFields(disallowUnknownFields bool) {
+	d.valueDecoder.setDisallowUnknownFields(disallowUnknownFields)
+}
+
 func (d *arrayDecoder) decodeStream(s *stream, p uintptr) error {
 	for {
 		switch s.char() {

decode_bool.go

@@ -58,6 +58,8 @@ func falseBytes(s *stream) error {
 	return nil
 }
 
+func (d *boolDecoder) setDisallowUnknownFields(_ bool) {}
+
 func (d *boolDecoder) decodeStream(s *stream, p uintptr) error {
 	s.skipWhiteSpace()
 	for {

decode_float.go

@@ -46,6 +46,8 @@ func floatBytes(s *stream) []byte {
 	return s.buf[start:s.cursor]
 }
 
+func (d *floatDecoder) setDisallowUnknownFields(_ bool) {}
+
 func (d *floatDecoder) decodeStreamByte(s *stream) ([]byte, error) {
 	for {
 		switch s.char() {

decode_int.go

@@ -49,6 +49,8 @@ var (
 	}
 )
 
+func (d *intDecoder) setDisallowUnknownFields(_ bool) {}
+
 func (d *intDecoder) decodeStreamByte(s *stream) ([]byte, error) {
 	for {
 		switch s.char() {

decode_interface.go

@@ -6,8 +6,9 @@ import (
 )
 
 type interfaceDecoder struct {
-	typ   *rtype
-	dummy unsafe.Pointer // for escape value
+	typ                   *rtype
+	dummy                 unsafe.Pointer // for escape value
+	disallowUnknownFields bool
 }
 
 func newInterfaceDecoder(typ *rtype) *interfaceDecoder {
@@ -16,6 +17,10 @@ func newInterfaceDecoder(typ *rtype) *interfaceDecoder {
 	}
 }
 
+func (d *interfaceDecoder) setDisallowUnknownFields(disallowUnknownFields bool) {
+	d.disallowUnknownFields = disallowUnknownFields
+}
+
 func (d *interfaceDecoder) numDecoder(s *stream) decoder {
 	if s.useNumber {
 		return newNumberDecoder(func(p uintptr, v Number) {
@@ -46,6 +51,7 @@ func (d *interfaceDecoder) decodeStream(s *stream, p uintptr) error {
 				newInterfaceDecoder(d.typ),
 				newInterfaceDecoder(d.typ),
 			)
+			dec.setDisallowUnknownFields(d.disallowUnknownFields)
 			if err := dec.decodeStream(s, uintptr(ptr)); err != nil {
 				return err
 			}
@@ -60,6 +66,7 @@ func (d *interfaceDecoder) decodeStream(s *stream, p uintptr) error {
 				d.typ,
 				d.typ.Size(),
 			)
+			dec.setDisallowUnknownFields(d.disallowUnknownFields)
 			if err := dec.decodeStream(s, uintptr(ptr)); err != nil {
 				return err
 			}
@@ -128,6 +135,7 @@ func (d *interfaceDecoder) decode(buf []byte, cursor int64, p uintptr) (int64, e
 			newInterfaceDecoder(d.typ),
 			newInterfaceDecoder(d.typ),
 		)
+		dec.setDisallowUnknownFields(d.disallowUnknownFields)
 		cursor, err := dec.decode(buf, cursor, uintptr(ptr))
 		if err != nil {
 			return 0, err
@@ -143,6 +151,7 @@ func (d *interfaceDecoder) decode(buf []byte, cursor int64, p uintptr) (int64, e
 			d.typ,
 			d.typ.Size(),
 		)
+		dec.setDisallowUnknownFields(d.disallowUnknownFields)
 		cursor, err := dec.decode(buf, cursor, uintptr(ptr))
 		if err != nil {
 			return 0, err

decode_map.go

@@ -26,6 +26,11 @@ func makemap(*rtype, int) unsafe.Pointer
 //go:noescape
 func mapassign(t *rtype, m unsafe.Pointer, key, val unsafe.Pointer)
 
+func (d *mapDecoder) setDisallowUnknownFields(disallowUnknownFields bool) {
+	d.keyDecoder.setDisallowUnknownFields(disallowUnknownFields)
+	d.valueDecoder.setDisallowUnknownFields(disallowUnknownFields)
+}
+
 func (d *mapDecoder) setKey(buf []byte, cursor int64, key interface{}) (int64, error) {
 	header := (*interfaceHeader)(unsafe.Pointer(&key))
 	return d.keyDecoder.decode(buf, cursor, uintptr(header.ptr))

decode_number.go

@@ -16,6 +16,8 @@ func newNumberDecoder(op func(uintptr, Number)) *numberDecoder {
 	}
 }
 
+func (d *numberDecoder) setDisallowUnknownFields(_ bool) {}
+
 func (d *numberDecoder) decodeStream(s *stream, p uintptr) error {
 	bytes, err := d.floatDecoder.decodeStreamByte(s)
 	if err != nil {

decode_ptr.go

@@ -16,6 +16,10 @@ func newPtrDecoder(dec decoder, typ *rtype) *ptrDecoder {
 //go:linkname unsafe_New reflect.unsafe_New
 func unsafe_New(*rtype) uintptr
 
+func (d *ptrDecoder) setDisallowUnknownFields(disallowUnknownFields bool) {
+	d.dec.setDisallowUnknownFields(disallowUnknownFields)
+}
+
 func (d *ptrDecoder) decodeStream(s *stream, p uintptr) error {
 	newptr := unsafe_New(d.typ)
 	if err := d.dec.decodeStream(s, newptr); err != nil {

decode_slice.go

@@ -56,6 +56,10 @@ func copySlice(elemType *rtype, dst, src reflect.SliceHeader) int
 //go:linkname newArray reflect.unsafe_NewArray
 func newArray(*rtype, int) unsafe.Pointer
 
+func (d *sliceDecoder) setDisallowUnknownFields(disallowUnknownFields bool) {
+	d.valueDecoder.setDisallowUnknownFields(disallowUnknownFields)
+}
+
 func (d *sliceDecoder) decodeStream(s *stream, p uintptr) error {
 	for {
 		switch s.char() {

decode_string.go

@@ -11,6 +11,8 @@ func newStringDecoder() *stringDecoder {
 	return &stringDecoder{}
 }
 
+func (d *stringDecoder) setDisallowUnknownFields(_ bool) {}
+
 func (d *stringDecoder) decodeStream(s *stream, p uintptr) error {
 	bytes, err := d.decodeStreamByte(s)
 	if err != nil {

decode_struct.go

@@ -1,6 +1,7 @@
 package json
 
 import (
+	"fmt"
 	"unsafe"
 )
 
@@ -10,8 +11,9 @@ type structFieldSet struct {
 }
 
 type structDecoder struct {
-	fieldMap   map[string]*structFieldSet
-	keyDecoder *stringDecoder
+	fieldMap              map[string]*structFieldSet
+	keyDecoder            *stringDecoder
+	disallowUnknownFields bool
 }
 
 func newStructDecoder(fieldMap map[string]*structFieldSet) *structDecoder {
@@ -21,6 +23,13 @@ func newStructDecoder(fieldMap map[string]*structFieldSet) *structDecoder {
 	}
 }
 
+func (d *structDecoder) setDisallowUnknownFields(disallowUnknownFields bool) {
+	d.disallowUnknownFields = disallowUnknownFields
+	for _, field := range d.fieldMap {
+		field.dec.setDisallowUnknownFields(disallowUnknownFields)
+	}
+}
+
 func (d *structDecoder) decodeStream(s *stream, p uintptr) error {
 	s.skipWhiteSpace()
 	if s.char() == nul {
@@ -56,6 +65,8 @@ func (d *structDecoder) decodeStream(s *stream, p uintptr) error {
 			if err := field.dec.decodeStream(s, p+field.offset); err != nil {
 				return err
 			}
+		} else if d.disallowUnknownFields {
+			return fmt.Errorf("json: unknown field %q", k)
 		} else {
 			if err := s.skipValue(); err != nil {
 				return err
@@ -110,6 +121,8 @@ func (d *structDecoder) decode(buf []byte, cursor int64, p uintptr) (int64, erro
 				return 0, err
 			}
 			cursor = c
+		} else if d.disallowUnknownFields {
+			return 0, fmt.Errorf("json: unknown field %q", k)
 		} else {
 			c, err := skipValue(buf, cursor)
 			if err != nil {

decode_test.go

@@ -225,6 +225,21 @@ func Test_Decoder_UseNumber(t *testing.T) {
 	assertEq(t, "json.Number", "json.Number", fmt.Sprintf("%T", v["a"]))
 }
 
+func Test_Decoder_DisallowUnknownFields(t *testing.T) {
+	dec := json.NewDecoder(strings.NewReader(`{"x": 1}`))
+	dec.DisallowUnknownFields()
+	var v struct {
+		x int
+	}
+	err := dec.Decode(&v)
+	if err == nil {
+		t.Fatal("expected unknown field error")
+	}
+	if err.Error() != `json: unknown field "x"` {
+		t.Fatal("expected unknown field error")
+	}
+}
+
 type unmarshalJSON struct {
 	v int
 }

decode_uint.go

@@ -24,6 +24,8 @@ func (d *uintDecoder) parseUint(b []byte) uint64 {
 	return sum
 }
 
+func (d *uintDecoder) setDisallowUnknownFields(_ bool) {}
+
 func (d *uintDecoder) decodeStreamByte(s *stream) ([]byte, error) {
 	for {
 		switch s.char() {

decode_unmarshal_json.go

@@ -12,6 +12,8 @@ func newUnmarshalJSONDecoder(typ *rtype) *unmarshalJSONDecoder {
 	return &unmarshalJSONDecoder{typ: typ}
 }
 
+func (d *unmarshalJSONDecoder) setDisallowUnknownFields(_ bool) {}
+
 func (d *unmarshalJSONDecoder) decodeStream(s *stream, p uintptr) error {
 	s.skipWhiteSpace()
 	start := s.cursor

decode_unmarshal_text.go

@@ -13,6 +13,8 @@ func newUnmarshalTextDecoder(typ *rtype) *unmarshalTextDecoder {
 	return &unmarshalTextDecoder{typ: typ}
 }
 
+func (d *unmarshalTextDecoder) setDisallowUnknownFields(_ bool) {}
+
 func (d *unmarshalTextDecoder) decodeStream(s *stream, p uintptr) error {
 	s.skipWhiteSpace()
 	start := s.cursor