From 6eb23deb6f2da36c949088e12839fae70d5b0e0c Mon Sep 17 00:00:00 2001
From: Masaaki Goshima <goccy54@gmail.com>
Date: Thu, 18 Feb 2021 17:46:28 +0900
Subject: [PATCH] Fix decoding of embedded unexported pointer field

---
 decode_compile.go | 20 ++++++++++++++++----
 decode_struct.go  |  7 +++++++
 decode_test.go    |  6 ++----
 3 files changed, 25 insertions(+), 8 deletions(-)

diff --git a/decode_compile.go b/decode_compile.go
index b563d50..da9f1c0 100644
--- a/decode_compile.go
+++ b/decode_compile.go
@@ -1,8 +1,10 @@
 package json
 
 import (
+	"fmt"
 	"reflect"
 	"strings"
+	"unicode"
 	"unsafe"
 )
 
@@ -247,7 +249,7 @@ func decodeCompileInterface(typ *rtype, structName, fieldName string) (decoder,
 	return newInterfaceDecoder(typ, structName, fieldName), nil
 }
 
-func decodeRemoveConflictFields(fieldMap map[string]*structFieldSet, conflictedMap map[string]struct{}, dec *structDecoder, baseOffset uintptr) {
+func decodeRemoveConflictFields(fieldMap map[string]*structFieldSet, conflictedMap map[string]struct{}, dec *structDecoder, field reflect.StructField) {
 	for k, v := range dec.fieldMap {
 		if _, exists := conflictedMap[k]; exists {
 			// already conflicted key
@@ -257,7 +259,7 @@ func decodeRemoveConflictFields(fieldMap map[string]*structFieldSet, conflictedM
 		if !exists {
 			fieldSet := &structFieldSet{
 				dec:         v.dec,
-				offset:      baseOffset + v.offset,
+				offset:      field.Offset + v.offset,
 				isTaggedKey: v.isTaggedKey,
 				key:         k,
 				keyLen:      int64(len(k)),
@@ -281,7 +283,7 @@ func decodeRemoveConflictFields(fieldMap map[string]*structFieldSet, conflictedM
 			if v.isTaggedKey {
 				fieldSet := &structFieldSet{
 					dec:         v.dec,
-					offset:      baseOffset + v.offset,
+					offset:      field.Offset + v.offset,
 					isTaggedKey: v.isTaggedKey,
 					key:         k,
 					keyLen:      int64(len(k)),
@@ -318,6 +320,7 @@ func decodeCompileStruct(typ *rtype, structName, fieldName string, structTypeToD
 		if isIgnoredStructField(field) {
 			continue
 		}
+		isUnexportedField := unicode.IsLower([]rune(field.Name)[0])
 		tag := structTagFromField(field)
 		dec, err := decodeCompile(type2rtype(field.Type), structName, field.Name, structTypeToDecoder)
 		if err != nil {
@@ -329,13 +332,20 @@ func decodeCompileStruct(typ *rtype, structName, fieldName string, structTypeToD
 					// recursive definition
 					continue
 				}
-				decodeRemoveConflictFields(fieldMap, conflictedMap, stDec, field.Offset)
+				decodeRemoveConflictFields(fieldMap, conflictedMap, stDec, field)
 			} else if pdec, ok := dec.(*ptrDecoder); ok {
 				contentDec := pdec.contentDecoder()
 				if pdec.typ == typ {
 					// recursive definition
 					continue
 				}
+				var fieldSetErr error
+				if isUnexportedField {
+					fieldSetErr = fmt.Errorf(
+						"json: cannot set embedded pointer to unexported struct: %v",
+						field.Type.Elem(),
+					)
+				}
 				if dec, ok := contentDec.(*structDecoder); ok {
 					for k, v := range dec.fieldMap {
 						if _, exists := conflictedMap[k]; exists {
@@ -350,6 +360,7 @@ func decodeCompileStruct(typ *rtype, structName, fieldName string, structTypeToD
 								isTaggedKey: v.isTaggedKey,
 								key:         k,
 								keyLen:      int64(len(k)),
+								err:         fieldSetErr,
 							}
 							fieldMap[k] = fieldSet
 							lower := strings.ToLower(k)
@@ -374,6 +385,7 @@ func decodeCompileStruct(typ *rtype, structName, fieldName string, structTypeToD
 									isTaggedKey: v.isTaggedKey,
 									key:         k,
 									keyLen:      int64(len(k)),
+									err:         fieldSetErr,
 								}
 								fieldMap[k] = fieldSet
 								lower := strings.ToLower(k)
diff --git a/decode_struct.go b/decode_struct.go
index f1e347a..4264620 100644
--- a/decode_struct.go
+++ b/decode_struct.go
@@ -15,6 +15,7 @@ type structFieldSet struct {
 	isTaggedKey bool
 	key         string
 	keyLen      int64
+	err         error
 }
 
 type structDecoder struct {
@@ -524,6 +525,9 @@ func (d *structDecoder) decodeStream(s *stream, p unsafe.Pointer) error {
 			}
 		}
 		if field != nil {
+			if field.err != nil {
+				return field.err
+			}
 			if err := field.dec.decodeStream(s, unsafe.Pointer(uintptr(p)+field.offset)); err != nil {
 				return err
 			}
@@ -591,6 +595,9 @@ func (d *structDecoder) decode(buf []byte, cursor int64, p unsafe.Pointer) (int6
 			return 0, errExpected("object value after colon", cursor)
 		}
 		if field != nil {
+			if field.err != nil {
+				return 0, field.err
+			}
 			c, err := field.dec.decode(buf, cursor, unsafe.Pointer(uintptr(p)+field.offset))
 			if err != nil {
 				return 0, err
diff --git a/decode_test.go b/decode_test.go
index e5e7da9..26c91fe 100644
--- a/decode_test.go
+++ b/decode_test.go
@@ -2539,7 +2539,6 @@ func TestInvalidStringOption(t *testing.T) {
 }
 */
 
-/*
 // Test unmarshal behavior with regards to embedded unexported structs.
 //
 // (Issue 21357) If the embedded struct is a pointer and is unallocated,
@@ -2604,7 +2603,7 @@ func TestUnmarshalEmbeddedUnexported(t *testing.T) {
 		in:  `{"R":2,"Q":1}`,
 		ptr: new(S1),
 		out: &S1{R: 2},
-		err: fmt.Errorf("json: cannot set embedded pointer to unexported struct: json.embed1"),
+		err: fmt.Errorf("json: cannot set embedded pointer to unexported struct: json_test.embed1"),
 	}, {
 		// The top level Q field takes precedence.
 		in:  `{"Q":1}`,
@@ -2626,7 +2625,7 @@ func TestUnmarshalEmbeddedUnexported(t *testing.T) {
 		in:  `{"R":2,"Q":1}`,
 		ptr: new(S5),
 		out: &S5{R: 2},
-		err: fmt.Errorf("json: cannot set embedded pointer to unexported struct: json.embed3"),
+		err: fmt.Errorf("json: cannot set embedded pointer to unexported struct: json_test.embed3"),
 	}, {
 		// Issue 24152, ensure decodeState.indirect does not panic.
 		in:  `{"embed1": {"Q": 1}}`,
@@ -2670,7 +2669,6 @@ func TestUnmarshalEmbeddedUnexported(t *testing.T) {
 		}
 	}
 }
-*/
 
 /*
 func TestUnmarshalErrorAfterMultipleJSON(t *testing.T) {