fix reading null virtual field of a struct

meta.go

@@ -6,6 +6,17 @@ func ReadGeneric(r Reader, createFunc StructFactory, field string) (Readable, er
 	if err := r.BeginContainer(field); err != nil {
 		return nil, err
 	}
+	size, err := r.ContainerSize()
+	if err != nil {
+		return nil, err
+	}
+	if size == 0 {
+		if err := r.EndContainer(); err != nil {
+			return nil, err
+		}
+
+		return nil, nil
+	}
 
 	var classId uint32
 	if err := r.ReadUint32(&classId, classField); err != nil {

msgpack_assoc_reader.go

@@ -559,6 +559,19 @@ func (rd *msgpackAssocReader) beginContainer(field string) error {
 	}
 
 	switch {
+	case code == msgpcode.Nil:
+		if err := rd.dec.DecodeNil(); err != nil {
+			return errors.WithStack(err)
+		}
+		rd.stack = append(rd.stack, rd.curr)
+		rd.curr = assocReadContainer{
+			started: true,
+			length:  0,
+			assoc:   true,
+			values:  make(map[string]msgpack.RawMessage),
+			reader:  rd.dec.Buffered(),
+		}
+
 	case msgpcode.IsFixedMap(code), code == msgpcode.Map16, code == msgpcode.Map32:
 		l, err := rd.dec.DecodeMapLen()
 		if err != nil {

msgpack_assoc_reader_test.go

@@ -11,8 +11,8 @@ import (
 
 func TestAssocMsgpackReader(t *testing.T) {
 	t.Run("reading parent", func(t *testing.T) {
-		// {"f1":"blabla","f3":[2,4,6],"f2":{"field":1},"f4":[{"field":10},{"field":1024}]}
-		src := "84a26631a6626c61626c61a2663393020406a2663281a56669656c6401a266349281a56669656c640a81a56669656c64cd0400"
+		// {"f1":"blabla","f3":[2,4,6],"f2":{"field":1},"f4":[{"field":10},{"field":1024}],"f5":null}
+		src := "85A26631A6626C61626C61A2663393020406A2663281A56669656C6401A266349281A56669656C640A81A56669656C64CD0400A26635C0"
 
 		expected := TestParent{
 			Field1: "blabla",
@@ -39,7 +39,7 @@ func TestAssocMsgpackReader(t *testing.T) {
 
 	t.Run("reading child", func(t *testing.T) {
 		// {"f":"qwerty","f1":"blabla","f3":[2,4,6],"f2":{"field":1},"f4":[{"field":10},{"field":1024}]}
-		src := "85a166a6717765727479a26631a6626c61626c61a2663393020406a2663281a56669656c6401a266349281a56669656c640a81a56669656c64cd0400"
+		src := "85A166A6717765727479A26631A6626C61626C61A2663393020406A2663281A56669656C6401A266349281A56669656C640A81A56669656C64CD0400"
 
 		expected := TestChild{
 			Field: "qwerty",
@@ -68,8 +68,8 @@ func TestAssocMsgpackReader(t *testing.T) {
 	})
 
 	t.Run("fail reading parent as array", func(t *testing.T) {
-		// ["blabla",[1],[2,4,6],[[10],[1024]]]
-		src := "94a6626c61626c6191019302040692910a91cd0400"
+		// ["blabla",[1],[2,4,6],[[10],[1024]],null]
+		src := "95A6626C61626C6191019302040692910A91CD0400C0"
 
 		expected := TestParent{}
 
@@ -85,8 +85,8 @@ func TestAssocMsgpackReader(t *testing.T) {
 	})
 
 	t.Run("fail reading parent as array with maps", func(t *testing.T) {
-		// ["blabla",{"field":1},[2,4,6],[{"field":10},{"field":1024}]]
-		src := "94a6626c61626c6181a56669656c6401930204069281a56669656c640a81a56669656c64cd0400"
+		// ["blabla",{"field":1},[2,4,6],[{"field":10},{"field":1024}],null]
+		src := "95A6626C61626C6181A56669656C6401930204069281A56669656C640A81A56669656C64CD0400C0"
 
 		expected := TestParent{}
 
@@ -102,8 +102,8 @@ func TestAssocMsgpackReader(t *testing.T) {
 	})
 
 	t.Run("fail reading child as array", func(t *testing.T) {
-		// ["blabla",[1],[2,4,6],[[10],[1024]],"qwerty"]
-		src := "95a6626c61626c6191019302040692910a91cd0400a6717765727479"
+		// ["blabla",[1],[2,4,6],[[10],[1024]],null,"qwerty"]
+		src := "96A6626C61626C6191019302040692910A91CD0400C0A6717765727479"
 
 		expected := TestChild{}
 

msgpack_reader.go

@@ -139,6 +139,15 @@ func (rd *msgpackReader) beginContainer(field string) error {
 	}
 
 	switch {
+	case code == msgpcode.Nil:
+		if err := rd.dec.DecodeNil(); err != nil {
+			return errors.WithStack(err)
+		}
+		rd.stack = append(rd.stack, rd.curr)
+		rd.curr = readContainer{
+			length: 0,
+		}
+
 	case msgpcode.IsFixedArray(code), code == msgpcode.Array16, code == msgpcode.Array32:
 		l, err := rd.dec.DecodeArrayLen()
 		if err != nil {

msgpack_reader_test.go

@@ -11,8 +11,8 @@ import (
 
 func TestMsgpackReader(t *testing.T) {
 	t.Run("reading parent", func(t *testing.T) {
-		// ["blabla",[1],[2,4,6],[[10],[1024]]]
-		src := "94a6626c61626c6191019302040692910a91cd0400"
+		// ["blabla",[1],[2,4,6],[[10],[1024]],null]
+		src := "95A6626C61626C6191019302040692910A91CD0400C0"
 
 		expected := TestParent{
 			Field1: "blabla",
@@ -38,8 +38,8 @@ func TestMsgpackReader(t *testing.T) {
 	})
 
 	t.Run("reading child", func(t *testing.T) {
-		// ["blabla",[1],[2,4,6],[[10],[1024]],"qwerty"]
-		src := "95a6626c61626c6191019302040692910a91cd0400a6717765727479"
+		// ["blabla",[1],[2,4,6],[[10],[1024]],null,"qwerty"]
+		src := "96A6626C61626C6191019302040692910A91CD0400C0A6717765727479"
 
 		expected := TestChild{
 			Field: "qwerty",

structs_test.go

@@ -2,13 +2,39 @@ package meta_test
 
 import (
 	"git.bit5.ru/backend/meta/v5"
+	"github.com/pkg/errors"
 )
 
+func CreateTestParent(id uint32) (meta.Readable, error) {
+	if id == 111 {
+		return &TestParent{}, nil
+	}
+	return nil, errors.Errorf("wrong id")
+}
+
 type TestParent struct {
-	Field1 string    `json:"f1" msgpack:"f1"`
-	Field2 TestFoo   `json:"f2" msgpack:"f2"`
-	Field3 []int8    `json:"f3" msgpack:"f3"`
-	Field4 []TestFoo `json:"f4" msgpack:"f4"`
+	Field1 string      `json:"f1" msgpack:"f1"`
+	Field2 TestFoo     `json:"f2" msgpack:"f2"`
+	Field3 []int8      `json:"f3" msgpack:"f3"`
+	Field4 []TestFoo   `json:"f4" msgpack:"f4"`
+	Field5 ITestParent `json:"f5" msgpack:"f5"`
+}
+
+type ITestParent interface {
+	meta.Struct
+	PtrTestParent() *TestParent
+}
+
+func (s *TestParent) PtrTestParent() *TestParent {
+	return s
+}
+
+func (s *TestParent) ClassId() uint32 {
+	return 111
+}
+
+func (s *TestParent) ClassName() string {
+	return "TestParent"
 }
 
 func (s *TestParent) Reset() {
@@ -26,6 +52,8 @@ func (s *TestParent) Reset() {
 		s.Field4 = s.Field4[:0]
 	}
 
+	s.Field5 = nil
+
 }
 
 func (s *TestParent) Read(reader meta.Reader) error {
@@ -46,8 +74,8 @@ func (s *TestParent) ReadFields(reader meta.Reader) error {
 		return err
 	}
 
-	if contSize < 4 {
-		contSize = 4
+	if contSize < 5 {
+		contSize = 5
 	}
 
 	if contSize <= 0 {
@@ -128,6 +156,21 @@ func (s *TestParent) ReadFields(reader meta.Reader) error {
 		return err
 	}
 
+	if contSize <= 0 {
+		return nil
+	}
+
+	contSize--
+	if v, err := meta.ReadGeneric(reader, CreateTestParent, "f5"); err != nil {
+		if err != meta.FieldNotFound {
+			return err
+		}
+	} else {
+		if v != nil {
+			s.Field5 = v.(ITestParent)
+		}
+	}
+
 	return nil
 }
 
@@ -191,6 +234,10 @@ func (s *TestParent) WriteFields(writer meta.Writer) error {
 	return nil
 }
 
+func (s *TestParent) FieldsCount() int {
+	return 5
+}
+
 type TestChild struct {
 	TestParent