VOL-2017 voltha-lib moved from voltha-go;
release version 2.2.1

Based on voltha-go commit 5259f8e52b3e3f5c7ad422a4b0e506e1d07f6b36

Change-Id: I8bbecdf456e420714a4016120eafc0d237c80565
diff --git a/pkg/db/model/data_revision.go b/pkg/db/model/data_revision.go
new file mode 100644
index 0000000..d349ec2
--- /dev/null
+++ b/pkg/db/model/data_revision.go
@@ -0,0 +1,73 @@
+/*
+ * Copyright 2018-present Open Networking Foundation
+
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+
+ * http://www.apache.org/licenses/LICENSE-2.0
+
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package model
+
+import (
+	"bytes"
+	"crypto/md5"
+	"encoding/json"
+	"fmt"
+	"github.com/golang/protobuf/proto"
+	"github.com/opencord/voltha-lib-go/pkg/common/log"
+	"reflect"
+)
+
+// DataRevision stores the data associated to a revision along with its calculated checksum hash value
+type DataRevision struct {
+	Data interface{}
+	Hash string
+}
+
+// NewDataRevision creates a new instance of a DataRevision structure
+func NewDataRevision(root *root, data interface{}) *DataRevision {
+	dr := DataRevision{}
+	dr.Data = data
+	dr.Hash = dr.hashData(root, data)
+
+	return &dr
+}
+
+func (dr *DataRevision) hashData(root *root, data interface{}) string {
+	var buffer bytes.Buffer
+
+	if IsProtoMessage(data) {
+		if pbdata, err := proto.Marshal(data.(proto.Message)); err != nil {
+			log.Debugf("problem to marshal protobuf data --> err: %s", err.Error())
+		} else {
+			buffer.Write(pbdata)
+			// To ensure uniqueness in case data is nil, also include data type
+			buffer.Write([]byte(reflect.TypeOf(data).String()))
+		}
+
+	} else if reflect.ValueOf(data).IsValid() {
+		dataObj := reflect.New(reflect.TypeOf(data).Elem())
+		if json, err := json.Marshal(dataObj.Interface()); err != nil {
+			log.Debugf("problem to marshal data --> err: %s", err.Error())
+		} else {
+			buffer.Write(json)
+		}
+	} else {
+		dataObj := reflect.New(reflect.TypeOf(data).Elem())
+		buffer.Write(dataObj.Bytes())
+	}
+
+	// Add the root pointer that owns the current data for extra uniqueness
+	rootPtr := fmt.Sprintf("%p", root)
+	buffer.Write([]byte(rootPtr))
+
+	return fmt.Sprintf("%x", md5.Sum(buffer.Bytes()))[:12]
+}