From 6ebd44bb936b77ea6f33d2061b80c93f9d401b9b Mon Sep 17 00:00:00 2001
From: Masaaki Goshima <goccy54@gmail.com>
Date: Fri, 12 Feb 2021 20:05:44 +0900
Subject: [PATCH] Fix decoding of pointer of empty interface type

---
 decode_interface.go | 25 ++++++++++++++++---------
 1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/decode_interface.go b/decode_interface.go
index a46abe5..3019b05 100644
--- a/decode_interface.go
+++ b/decode_interface.go
@@ -13,6 +13,12 @@ type interfaceDecoder struct {
 }
 
 func newInterfaceDecoder(typ *rtype, structName, fieldName string) *interfaceDecoder {
+	if typ == emptyInterfaceType {
+		// If type is the same as emptyInterface ( `interface{}` ),
+		// the address of `*interface{}` type will be passed when actually decoding,
+		// so type must be converted to pointer type.
+		typ = type2rtype(reflect.New(rtype2type(typ)).Type())
+	}
 	return &interfaceDecoder{
 		typ:        typ,
 		structName: structName,
@@ -32,7 +38,8 @@ func (d *interfaceDecoder) numDecoder(s *stream) decoder {
 }
 
 var (
-	interfaceMapType = type2rtype(
+	emptyInterfaceType = type2rtype(reflect.TypeOf((*interface{})(nil)).Elem())
+	interfaceMapType   = type2rtype(
 		reflect.TypeOf((*map[string]interface{})(nil)).Elem(),
 	)
 	stringType = type2rtype(
@@ -82,7 +89,7 @@ func (d *interfaceDecoder) decodeStreamEmptyInterface(s *stream, p unsafe.Pointe
 				stringType,
 				newStringDecoder(d.structName, d.fieldName),
 				interfaceMapType.Elem(),
-				newInterfaceDecoder(d.typ, d.structName, d.fieldName),
+				newInterfaceDecoder(emptyInterfaceType, d.structName, d.fieldName),
 				d.structName,
 				d.fieldName,
 			).decodeStream(s, ptr); err != nil {
@@ -94,9 +101,9 @@ func (d *interfaceDecoder) decodeStreamEmptyInterface(s *stream, p unsafe.Pointe
 			var v []interface{}
 			ptr := unsafe.Pointer(&v)
 			if err := newSliceDecoder(
-				newInterfaceDecoder(d.typ, d.structName, d.fieldName),
-				d.typ,
-				d.typ.Size(),
+				newInterfaceDecoder(emptyInterfaceType, d.structName, d.fieldName),
+				emptyInterfaceType,
+				emptyInterfaceType.Size(),
 				d.structName,
 				d.fieldName,
 			).decodeStream(s, ptr); err != nil {
@@ -246,7 +253,7 @@ func (d *interfaceDecoder) decodeEmptyInterface(buf []byte, cursor int64, p unsa
 			stringType,
 			newStringDecoder(d.structName, d.fieldName),
 			interfaceMapType.Elem(),
-			newInterfaceDecoder(d.typ, d.structName, d.fieldName),
+			newInterfaceDecoder(emptyInterfaceType, d.structName, d.fieldName),
 			d.structName, d.fieldName,
 		)
 		cursor, err := dec.decode(buf, cursor, ptr)
@@ -259,9 +266,9 @@ func (d *interfaceDecoder) decodeEmptyInterface(buf []byte, cursor int64, p unsa
 		var v []interface{}
 		ptr := unsafe.Pointer(&v)
 		dec := newSliceDecoder(
-			newInterfaceDecoder(d.typ, d.structName, d.fieldName),
-			d.typ,
-			d.typ.Size(),
+			newInterfaceDecoder(emptyInterfaceType, d.structName, d.fieldName),
+			emptyInterfaceType,
+			emptyInterfaceType.Size(),
 			d.structName, d.fieldName,
 		)
 		cursor, err := dec.decode(buf, cursor, ptr)