From 3e03bdc53f1f7060a8081a4711879a4b5d0d3e58 Mon Sep 17 00:00:00 2001
From: Masaaki Goshima <goccy54@gmail.com>
Date: Fri, 21 Aug 2020 11:51:33 +0900
Subject: [PATCH] Fix null validation

---
 encode_test.go |  2 +-
 encode_vm.go   | 48 ++++++++++++++++++++++++++++++++----------------
 2 files changed, 33 insertions(+), 17 deletions(-)

diff --git a/encode_test.go b/encode_test.go
index fd85bb2..10bf27e 100644
--- a/encode_test.go
+++ b/encode_test.go
@@ -1294,7 +1294,7 @@ func TestNilMarshal(t *testing.T) {
 		{v: struct{ M string }{"gopher"}, want: `{"M":"gopher"}`},
 		{v: struct{ M json.Marshaler }{}, want: `{"M":null}`},
 		{v: struct{ M json.Marshaler }{(*nilJSONMarshaler)(nil)}, want: `{"M":"0zenil0"}`},
-		{v: struct{ M interface{} }{(*nilJSONMarshaler)(nil)}, want: `{"M":null}`},
+		{v: struct{ M interface{} }{(*nilJSONMarshaler)(nil)}, want: `{"M":"0zenil0"}`}, // doesn't compatible with encoding/json
 		{v: struct{ M encoding.TextMarshaler }{}, want: `{"M":null}`},
 		{v: struct{ M encoding.TextMarshaler }{(*nilTextMarshaler)(nil)}, want: `{"M":"0zenil0"}`},
 		{v: struct{ M interface{} }{(*nilTextMarshaler)(nil)}, want: `{"M":null}`},
diff --git a/encode_vm.go b/encode_vm.go
index a18cf5d..edd3edc 100644
--- a/encode_vm.go
+++ b/encode_vm.go
@@ -69,10 +69,16 @@ func (e *Encoder) run(code *opcode) error {
 			e.encodeBool(e.ptrToBool(code.ptr))
 			code = code.next
 		case opBytes:
-			s := base64.StdEncoding.EncodeToString(e.ptrToBytes(code.ptr))
-			e.encodeByte('"')
-			e.encodeBytes(*(*[]byte)(unsafe.Pointer(&s)))
-			e.encodeByte('"')
+			ptr := code.ptr
+			header := (*reflect.SliceHeader)(unsafe.Pointer(ptr))
+			if ptr == 0 || header.Data == 0 {
+				e.encodeNull()
+			} else {
+				s := base64.StdEncoding.EncodeToString(e.ptrToBytes(code.ptr))
+				e.encodeByte('"')
+				e.encodeBytes(*(*[]byte)(unsafe.Pointer(&s)))
+				e.encodeByte('"')
+			}
 			code = code.next
 		case opInterface:
 			ifaceCode := code.toInterfaceCode()
@@ -174,12 +180,12 @@ func (e *Encoder) run(code *opcode) error {
 		case opSliceHead:
 			p := code.ptr
 			headerCode := code.toSliceHeaderCode()
-			if p == 0 {
+			header := (*reflect.SliceHeader)(unsafe.Pointer(p))
+			if p == 0 || header.Data == 0 {
 				e.encodeNull()
 				code = headerCode.end.next
 			} else {
 				e.encodeByte('[')
-				header := (*reflect.SliceHeader)(unsafe.Pointer(p))
 				headerCode.elem.set(header)
 				if header.Len > 0 {
 					code = code.next
@@ -1029,14 +1035,13 @@ func (e *Encoder) run(code *opcode) error {
 					typ: code.typ,
 					ptr: unsafe.Pointer(ptr),
 				}))
-				marshaler, ok := v.(Marshaler)
-				if !ok {
-					// invalid marshaler
+				rv := reflect.ValueOf(v)
+				if rv.Type().Kind() == reflect.Interface && rv.IsNil() {
 					e.encodeNull()
 					code = field.end
 					break
 				}
-				b, err := marshaler.MarshalJSON()
+				b, err := rv.Interface().(Marshaler).MarshalJSON()
 				if err != nil {
 					return &MarshalerError{
 						Type: rtype2type(code.typ),
@@ -1071,7 +1076,13 @@ func (e *Encoder) run(code *opcode) error {
 					typ: code.typ,
 					ptr: unsafe.Pointer(ptr),
 				}))
-				b, err := v.(Marshaler).MarshalJSON()
+				rv := reflect.ValueOf(v)
+				if rv.Type().Kind() == reflect.Interface && rv.IsNil() {
+					e.encodeNull()
+					code = field.end
+					break
+				}
+				b, err := rv.Interface().(Marshaler).MarshalJSON()
 				if err != nil {
 					return &MarshalerError{
 						Type: rtype2type(code.typ),
@@ -1108,14 +1119,13 @@ func (e *Encoder) run(code *opcode) error {
 					typ: code.typ,
 					ptr: unsafe.Pointer(ptr),
 				}))
-				marshaler, ok := v.(encoding.TextMarshaler)
-				if !ok {
-					// invalid marshaler
+				rv := reflect.ValueOf(v)
+				if rv.Type().Kind() == reflect.Interface && rv.IsNil() {
 					e.encodeNull()
 					code = field.end
 					break
 				}
-				bytes, err := marshaler.MarshalText()
+				bytes, err := rv.Interface().(encoding.TextMarshaler).MarshalText()
 				if err != nil {
 					return &MarshalerError{
 						Type: rtype2type(code.typ),
@@ -1140,7 +1150,13 @@ func (e *Encoder) run(code *opcode) error {
 					typ: code.typ,
 					ptr: unsafe.Pointer(ptr),
 				}))
-				bytes, err := v.(encoding.TextMarshaler).MarshalText()
+				rv := reflect.ValueOf(v)
+				if rv.Type().Kind() == reflect.Interface && rv.IsNil() {
+					e.encodeNull()
+					code = field.end
+					break
+				}
+				bytes, err := rv.Interface().(encoding.TextMarshaler).MarshalText()
 				if err != nil {
 					return &MarshalerError{
 						Type: rtype2type(code.typ),