versioning: add basic version decode for network config

pkg/version/conf.go

@@ -0,0 +1,37 @@
+// Copyright 2016 CNI authors
+//
+// 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 version
+
+import (
+	"encoding/json"
+	"fmt"
+)
+
+// ConfigDecoder can decode the CNI version available in network config data
+type ConfigDecoder struct{}
+
+func (*ConfigDecoder) Decode(jsonBytes []byte) (string, error) {
+	var conf struct {
+		CNIVersion string `json:"cniVersion"`
+	}
+	err := json.Unmarshal(jsonBytes, &conf)
+	if err != nil {
+		return "", fmt.Errorf("decoding version from network config: %s", err)
+	}
+	if conf.CNIVersion == "" {
+		return "0.1.0", nil
+	}
+	return conf.CNIVersion, nil
+}