versioning: misc cleanups

highlights:
 - NetConf struct finally includes cniVersion field
 - improve test coverage of current version report behavior
 - godoc a few key functions
 - allow tests to control version list reported by no-op plugin

pkg/version/plugin.go

@@ -0,0 +1,77 @@
+// 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"
+	"io"
+)
+
+// PluginInfo reports information about CNI versioning
+type PluginInfo interface {
+	// SupportedVersions returns one or more CNI spec versions that the plugin
+	// supports.  If input is provided in one of these versions, then the plugin
+	// promises to use the same CNI version in its response
+	SupportedVersions() []string
+
+	// Encode writes this CNI version information as JSON to the given Writer
+	Encode(io.Writer) error
+}
+
+type pluginInfo struct {
+	CNIVersion_        string   `json:"cniVersion"`
+	SupportedVersions_ []string `json:"supportedVersions,omitempty"`
+}
+
+func (p *pluginInfo) Encode(w io.Writer) error {
+	return json.NewEncoder(w).Encode(p)
+}
+
+func (p *pluginInfo) SupportedVersions() []string {
+	return p.SupportedVersions_
+}
+
+// PluginSupports returns a new PluginInfo that will report the given versions
+// as supported
+func PluginSupports(supportedVersions ...string) PluginInfo {
+	if len(supportedVersions) < 1 {
+		panic("programmer error: you must support at least one version")
+	}
+	return &pluginInfo{
+		CNIVersion_:        Current(),
+		SupportedVersions_: supportedVersions,
+	}
+}
+
+type PluginDecoder struct{}
+
+func (_ *PluginDecoder) Decode(jsonBytes []byte) (PluginInfo, error) {
+	var info pluginInfo
+	err := json.Unmarshal(jsonBytes, &info)
+	if err != nil {
+		return nil, fmt.Errorf("decoding version info: %s", err)
+	}
+	if info.CNIVersion_ == "" {
+		return nil, fmt.Errorf("decoding version info: missing field cniVersion")
+	}
+	if len(info.SupportedVersions_) == 0 {
+		if info.CNIVersion_ == "0.2.0" {
+			return PluginSupports("0.1.0", "0.2.0"), nil
+		}
+		return nil, fmt.Errorf("decoding version info: missing field supportedVersions")
+	}
+	return &info, nil
+}