[#168] container: Implement binary/JSON encoders/decoders on Container

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

v2/container/json.go

@@ -1,40 +1,10 @@
 package container
 
 import (
-	"errors"
-
 	container "github.com/nspcc-dev/neofs-api-go/v2/container/grpc"
 	"google.golang.org/protobuf/encoding/protojson"
 )
 
-var (
-	errEmptyInput = errors.New("empty input")
-)
-
-func ContainerToJSON(c *Container) ([]byte, error) {
-	if c == nil {
-		return nil, errEmptyInput
-	}
-
-	msg := ContainerToGRPCMessage(c)
-
-	return protojson.MarshalOptions{EmitUnpopulated: true}.Marshal(msg)
-}
-
-func ContainerFromJSON(data []byte) (*Container, error) {
-	if len(data) == 0 {
-		return nil, errEmptyInput
-	}
-
-	msg := new(container.Container)
-
-	if err := protojson.Unmarshal(data, msg); err != nil {
-		return nil, err
-	}
-
-	return ContainerFromGRPCMessage(msg), nil
-}
-
 func (a *Attribute) MarshalJSON() ([]byte, error) {
 	return protojson.MarshalOptions{
 		EmitUnpopulated: true,
@@ -54,3 +24,23 @@ func (a *Attribute) UnmarshalJSON(data []byte) error {
 
 	return nil
 }
+
+func (c *Container) MarshalJSON() ([]byte, error) {
+	return protojson.MarshalOptions{
+		EmitUnpopulated: true,
+	}.Marshal(
+		ContainerToGRPCMessage(c),
+	)
+}
+
+func (c *Container) UnmarshalJSON(data []byte) error {
+	msg := new(container.Container)
+
+	if err := protojson.Unmarshal(data, msg); err != nil {
+		return err
+	}
+
+	*c = *ContainerFromGRPCMessage(msg)
+
+	return nil
+}