pkg/skel: plugins now respond to VERSION command

To support CNI spec versioning, plugins must be able to report version
information to container runtimes.

skel/skel.go

@@ -24,6 +24,7 @@ import (
 	"os"
 
 	"github.com/containernetworking/cni/pkg/types"
+	"github.com/containernetworking/cni/pkg/version"
 )
 
 // CmdArgs captures all the arguments passed in to the plugin
@@ -40,7 +41,9 @@ type CmdArgs struct {
 type dispatcher struct {
 	Getenv    func(string) string
 	Stdin     io.Reader
+	Stdout    io.Writer
 	Stderr    io.Writer
+	Versioner version.PluginVersioner
 }
 
 type reqForCmdEntry map[string]bool
@@ -154,6 +157,9 @@ func (t *dispatcher) pluginMain(cmdAdd, cmdDel func(_ *CmdArgs) error) *types.Er
 	case "DEL":
 		err = cmdDel(cmdArgs)
 
+	case "VERSION":
+		err = t.Versioner.Encode(t.Stdout)
+
 	default:
 		return createTypedError("unknown CNI_COMMAND: %v", cmd)
 	}
@@ -174,7 +180,9 @@ func PluginMain(cmdAdd, cmdDel func(_ *CmdArgs) error) {
 	caller := dispatcher{
 		Getenv:    os.Getenv,
 		Stdin:     os.Stdin,
+		Stdout:    os.Stdout,
 		Stderr:    os.Stderr,
+		Versioner: version.DefaultPluginVersioner,
 	}
 
 	err := caller.pluginMain(cmdAdd, cmdDel)

skel/skel_test.go

@@ -21,6 +21,7 @@ import (
 	"strings"
 
 	"github.com/containernetworking/cni/pkg/types"
+	"github.com/containernetworking/cni/pkg/version"
 
 	"github.com/containernetworking/cni/pkg/testutils"
 	. "github.com/onsi/ginkgo"
@@ -48,7 +49,7 @@ var _ = Describe("dispatching to the correct callback", func() {
 	var (
 		environment     map[string]string
 		stdin           io.Reader
-		stderr          *bytes.Buffer
+		stdout, stderr  *bytes.Buffer
 		cmdAdd, cmdDel  *fakeCmd
 		dispatch        *dispatcher
 		expectedCmdArgs *CmdArgs
@@ -64,11 +65,15 @@ var _ = Describe("dispatching to the correct callback", func() {
 			"CNI_PATH":        "/some/cni/path",
 		}
 		stdin = strings.NewReader(`{ "some": "config" }`)
+		stdout = &bytes.Buffer{}
 		stderr = &bytes.Buffer{}
+		versioner := &version.BasicVersioner{CNIVersion: "9.8.7"}
 		dispatch = &dispatcher{
 			Getenv:    func(key string) string { return environment[key] },
 			Stdin:     stdin,
+			Stdout:    stdout,
 			Stderr:    stderr,
+			Versioner: versioner,
 		}
 		cmdAdd = &fakeCmd{}
 		cmdDel = &fakeCmd{}
@@ -171,6 +176,36 @@ var _ = Describe("dispatching to the correct callback", func() {
 		)
 	})
 
+	Context("when the CNI_COMMAND is VERSION", func() {
+		BeforeEach(func() {
+			environment["CNI_COMMAND"] = "VERSION"
+		})
+
+		It("prints the version to stdout", func() {
+			err := dispatch.pluginMain(cmdAdd.Func, cmdDel.Func)
+
+			Expect(err).NotTo(HaveOccurred())
+			Expect(stdout).To(MatchJSON(`{ "cniVersion": "9.8.7" }`))
+		})
+
+		It("does not call cmdAdd or cmdDel", func() {
+			err := dispatch.pluginMain(cmdAdd.Func, cmdDel.Func)
+
+			Expect(err).NotTo(HaveOccurred())
+			Expect(cmdAdd.CallCount).To(Equal(0))
+			Expect(cmdDel.CallCount).To(Equal(0))
+		})
+
+		DescribeTable("VERSION does not need the usual env vars", envVarChecker,
+			Entry("command", "CNI_COMMAND", true),
+			Entry("container id", "CNI_CONTAINER_ID", false),
+			Entry("net ns", "CNI_NETNS", false),
+			Entry("if name", "CNI_IFNAME", false),
+			Entry("args", "CNI_ARGS", false),
+			Entry("path", "CNI_PATH", false),
+		)
+	})
+
 	Context("when the CNI_COMMAND is unrecognized", func() {
 		BeforeEach(func() {
 			environment["CNI_COMMAND"] = "NOPE"

version/version.go

@@ -0,0 +1,42 @@
+// 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"
+	"io"
+)
+
+// A PluginVersioner can encode information about its version
+type PluginVersioner interface {
+	Encode(io.Writer) error
+}
+
+// BasicVersioner is a PluginVersioner which reports a single cniVersion string
+type BasicVersioner struct {
+	CNIVersion string `json:"cniVersion"`
+}
+
+func (p *BasicVersioner) Encode(w io.Writer) error {
+	return json.NewEncoder(w).Encode(p)
+}
+
+// Current reports the version of the CNI spec implemented by this library
+func Current() string {
+	return "0.2.0"
+}
+
+// DefaultPluginVersioner reports the Current library spec version as the cniVersion
+var DefaultPluginVersioner = &BasicVersioner{CNIVersion: Current()}