[#77] protogen: Initial implementation

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>

util/proto/encoding/json.go

@@ -0,0 +1,48 @@
+package encoding
+
+import (
+	"encoding/json"
+	"fmt"
+
+	"google.golang.org/grpc/encoding"
+	"google.golang.org/protobuf/encoding/protojson"
+)
+
+// JSONCodec is easyjson codec used for code generated by protogen.
+// It is binary-level compatible with the standard protojson format, thus uses the same name.
+type JSONCodec struct{}
+
+var _ encoding.Codec = JSONCodec{}
+
+func init() {
+	encoding.RegisterCodec(JSONCodec{})
+}
+
+// Name implements the encoding.Codec interface.
+func (JSONCodec) Name() string { return "json" }
+
+// Marshal implements the encoding.Codec interface.
+func (JSONCodec) Marshal(v any) ([]byte, error) {
+	switch v := v.(type) {
+	case json.Marshaler:
+		return json.Marshal(v)
+	default:
+		if v := messageV2Of(v); v != nil {
+			return protojson.Marshal(v)
+		}
+		return nil, fmt.Errorf("failed to marshal, message is %T, want proto.Message", v)
+	}
+}
+
+// Unmarshal implements the encoding.Codec interface.
+func (JSONCodec) Unmarshal(data []byte, v any) error {
+	switch v := v.(type) {
+	case json.Unmarshaler:
+		return json.Unmarshal(data, v)
+	default:
+		if v := messageV2Of(v); v != nil {
+			return protojson.Unmarshal(data, v)
+		}
+		return fmt.Errorf("failed to unmarshal, message is %T, want proto.Message", v)
+	}
+}