rlp: fix pointer reuse

rlp/decode.go

@@ -309,6 +309,7 @@ func makePtrDecoder(typ reflect.Type) (decoder, error) {
 	dec := func(s *Stream, val reflect.Value) (err error) {
 		_, size, err := s.Kind()
 		if err != nil || size == 0 && s.byteval == 0 {
+			val.Set(reflect.Zero(typ)) // set to nil
 			return err
 		}
 		newval := val

rlp/decode_test.go

@@ -176,8 +176,6 @@ type recstruct struct {
 	Child *recstruct
 }
 
-var sharedByteArray [5]byte
-
 var (
 	veryBigInt = big.NewInt(0).Add(
 		big.NewInt(0).Lsh(big.NewInt(0xFFFFFFFFFFFFFF), 16),
@@ -185,6 +183,11 @@ var (
 	)
 )
 
+var (
+	sharedByteArray [5]byte
+	sharedPtr       = new(*int)
+)
+
 var decodeTests = []decodeTest{
 	// integers
 	{input: "05", ptr: new(uint32), value: uint32(5)},
@@ -268,6 +271,10 @@ var decodeTests = []decodeTest{
 	{input: "C109", ptr: new(*[]int), value: &[]int{9}},
 	{input: "C58403030303", ptr: new(*[][]byte), value: &[][]byte{{3, 3, 3, 3}}},
 
+	// pointer should be reset to nil
+	{input: "05", ptr: sharedPtr, value: intp(5)},
+	{input: "80", ptr: sharedPtr, value: (*int)(nil)},
+
 	// interface{}
 	{input: "00", ptr: new(interface{}), value: []byte{0}},
 	{input: "01", ptr: new(interface{}), value: []byte{1}},