versioning: plugins require version match with config

infer version 0.1.0 when config is missing an explicit "cniVersion" field

pkg/skel/skel.go

@@ -17,7 +17,6 @@
 package skel
 
 import (
-	"encoding/json"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -44,6 +43,9 @@ type dispatcher struct {
 	Stdin  io.Reader
 	Stdout io.Writer
 	Stderr io.Writer
+
+	ConfVersionDecoder version.ConfigDecoder
+	VersionReconciler  version.Reconciler
 }
 
 type reqForCmdEntry map[string]bool
@@ -144,16 +146,20 @@ func createTypedError(f string, args ...interface{}) *types.Error {
 	}
 }
 
-func (t *dispatcher) validateVersion(stdinData []byte) error {
-	var netconf types.NetConf
-	if err := json.Unmarshal(stdinData, &netconf); err != nil {
+func (t *dispatcher) checkVersionAndCall(cmdArgs *CmdArgs, pluginVersionInfo version.PluginInfo, toCall func(*CmdArgs) error) error {
+	configVersion, err := t.ConfVersionDecoder.Decode(cmdArgs.StdinData)
+	if err != nil {
 		return err
 	}
-	if netconf.CNIVersion == "" {
-		return fmt.Errorf("missing required config cniVersion")
+	verErr := t.VersionReconciler.Check(configVersion, pluginVersionInfo)
+	if verErr != nil {
+		return &types.Error{
+			Code:    types.ErrIncompatibleCNIVersion,
+			Msg:     "incompatible CNI versions",
+			Details: verErr.Details(),
+		}
 	}
-
-	return nil
+	return toCall(cmdArgs)
 }
 
 func (t *dispatcher) pluginMain(cmdAdd, cmdDel func(_ *CmdArgs) error, versionInfo version.PluginInfo) *types.Error {
@@ -162,20 +168,13 @@ func (t *dispatcher) pluginMain(cmdAdd, cmdDel func(_ *CmdArgs) error, versionIn
 		return createTypedError(err.Error())
 	}
 
-	if err = t.validateVersion(cmdArgs.StdinData); err != nil {
-		return createTypedError(err.Error())
-	}
-
 	switch cmd {
 	case "ADD":
-		err = cmdAdd(cmdArgs)
-
+		err = t.checkVersionAndCall(cmdArgs, versionInfo, cmdAdd)
 	case "DEL":
-		err = cmdDel(cmdArgs)
-
+		err = t.checkVersionAndCall(cmdArgs, versionInfo, cmdDel)
 	case "VERSION":
 		err = versionInfo.Encode(t.Stdout)
-
 	default:
 		return createTypedError("unknown CNI_COMMAND: %v", cmd)
 	}

pkg/skel/skel_test.go

@@ -150,14 +150,38 @@ var _ = Describe("dispatching to the correct callback", func() {
 				dispatch.Stdin = strings.NewReader(`{ "some": "config" }`)
 			})
 
-			It("immediately returns a useful error", func() {
-				err := dispatch.pluginMain(cmdAdd.Func, cmdDel.Func, versionInfo)
-				Expect(err).To(MatchError("missing required config cniVersion"))
+			Context("when the plugin supports version 0.1.0", func() {
+				BeforeEach(func() {
+					versionInfo = version.PluginSupports("0.1.0")
+					expectedCmdArgs.StdinData = []byte(`{ "some": "config" }`)
+				})
+
+				It("infers the config is 0.1.0 and calls the cmdAdd callback", func() {
+					err := dispatch.pluginMain(cmdAdd.Func, cmdDel.Func, versionInfo)
+					Expect(err).NotTo(HaveOccurred())
+
+					Expect(cmdAdd.CallCount).To(Equal(1))
+					Expect(cmdAdd.Received.CmdArgs).To(Equal(expectedCmdArgs))
+				})
 			})
 
-			It("does not call either callback", func() {
-				Expect(cmdAdd.CallCount).To(Equal(0))
-				Expect(cmdDel.CallCount).To(Equal(0))
+			Context("when the plugin does not support 0.1.0", func() {
+				BeforeEach(func() {
+					versionInfo = version.PluginSupports("4.3.2")
+				})
+
+				It("immediately returns a useful error", func() {
+					err := dispatch.pluginMain(cmdAdd.Func, cmdDel.Func, versionInfo)
+					Expect(err.Code).To(Equal(uint(1))) // see https://github.com/containernetworking/cni/blob/master/SPEC.md#well-known-error-codes
+					Expect(err.Msg).To(Equal("incompatible CNI versions"))
+					Expect(err.Details).To(Equal(`config is "0.1.0", plugin supports ["4.3.2"]`))
+				})
+
+				It("does not call either callback", func() {
+					dispatch.pluginMain(cmdAdd.Func, cmdDel.Func, versionInfo)
+					Expect(cmdAdd.CallCount).To(Equal(0))
+					Expect(cmdDel.CallCount).To(Equal(0))
+				})
 			})
 		})
 	})
@@ -223,6 +247,22 @@ var _ = Describe("dispatching to the correct callback", func() {
 			Entry("args", "CNI_ARGS", false),
 			Entry("path", "CNI_PATH", false),
 		)
+
+		Context("when the stdin is empty", func() {
+			BeforeEach(func() {
+				dispatch.Stdin = strings.NewReader("")
+			})
+
+			It("succeeds without error", func() {
+				err := dispatch.pluginMain(cmdAdd.Func, cmdDel.Func, versionInfo)
+
+				Expect(err).NotTo(HaveOccurred())
+				Expect(stdout).To(MatchJSON(`{
+					"cniVersion": "0.2.0",
+					"supportedVersions": ["9.8.7"]
+			}`))
+			})
+		})
 	})
 
 	Context("when the CNI_COMMAND is unrecognized", func() {