types: make Result an interface and move existing Result to separate package

pkg/version/legacy_examples/examples.go

@@ -23,6 +23,7 @@ import (
 	"sync"
 
 	"github.com/containernetworking/cni/pkg/types"
+	"github.com/containernetworking/cni/pkg/types/current"
 	"github.com/containernetworking/cni/pkg/version/testhelpers"
 )
 
@@ -114,8 +115,8 @@ func main() { skel.PluginMain(c, c) }
 //
 // As we change the CNI spec, the Result type and this value may change.
 // The text of the example plugins should not.
-var ExpectedResult = &types.Result{
-	IP4: &types.IPConfig{
+var ExpectedResult = &current.Result{
+	IP4: &current.IPConfig{
 		IP: net.IPNet{
 			IP:   net.ParseIP("10.1.2.3"),
 			Mask: net.CIDRMask(24, 32),

pkg/version/reconcile.go

@@ -17,12 +17,12 @@ package version
 import "fmt"
 
 type ErrorIncompatible struct {
-	Config string
-	Plugin []string
+	Config    string
+	Supported []string
 }
 
 func (e *ErrorIncompatible) Details() string {
-	return fmt.Sprintf("config is %q, plugin supports %q", e.Config, e.Plugin)
+	return fmt.Sprintf("config is %q, plugin supports %q", e.Config, e.Supported)
 }
 
 func (e *ErrorIncompatible) Error() string {
@@ -31,17 +31,19 @@ func (e *ErrorIncompatible) Error() string {
 
 type Reconciler struct{}
 
-func (*Reconciler) Check(configVersion string, pluginInfo PluginInfo) *ErrorIncompatible {
-	pluginVersions := pluginInfo.SupportedVersions()
+func (r *Reconciler) Check(configVersion string, pluginInfo PluginInfo) *ErrorIncompatible {
+	return r.CheckRaw(configVersion, pluginInfo.SupportedVersions())
+}
 
-	for _, pluginVersion := range pluginVersions {
-		if configVersion == pluginVersion {
+func (*Reconciler) CheckRaw(configVersion string, supportedVersions []string) *ErrorIncompatible {
+	for _, supportedVersion := range supportedVersions {
+		if configVersion == supportedVersion {
 			return nil
 		}
 	}
 
 	return &ErrorIncompatible{
-		Config: configVersion,
-		Plugin: pluginVersions,
+		Config:    configVersion,
+		Supported: supportedVersions,
 	}
 }

pkg/version/reconcile_test.go

@@ -41,8 +41,8 @@ var _ = Describe("Reconcile versions of net config with versions supported by pl
 			err := reconciler.Check("0.1.0", pluginInfo)
 
 			Expect(err).To(Equal(&version.ErrorIncompatible{
-				Config: "0.1.0",
-				Plugin: []string{"1.2.3", "4.3.2"},
+				Config:    "0.1.0",
+				Supported: []string{"1.2.3", "4.3.2"},
 			}))
 
 			Expect(err.Error()).To(Equal(`incompatible CNI versions: config is "0.1.0", plugin supports ["1.2.3" "4.3.2"]`))

pkg/version/version.go

@@ -14,6 +14,13 @@
 
 package version
 
+import (
+	"fmt"
+
+	"github.com/containernetworking/cni/pkg/types"
+	"github.com/containernetworking/cni/pkg/types/current"
+)
+
 // Current reports the version of the CNI spec implemented by this library
 func Current() string {
 	return "0.2.0"
@@ -27,3 +34,25 @@ func Current() string {
 // Any future CNI spec versions which meet this definition should be added to
 // this list.
 var Legacy = PluginSupports("0.1.0", "0.2.0")
+
+var resultFactories = []struct {
+	supportedVersions []string
+	newResult         types.ResultFactoryFunc
+}{
+	{current.SupportedVersions, current.NewResult},
+}
+
+// Finds a Result object matching the requested version (if any) and asks
+// that object to parse the plugin result, returning an error if parsing failed.
+func NewResult(version string, resultBytes []byte) (types.Result, error) {
+	reconciler := &Reconciler{}
+	for _, resultFactory := range resultFactories {
+		err := reconciler.CheckRaw(version, resultFactory.supportedVersions)
+		if err == nil {
+			// Result supports this version
+			return resultFactory.newResult(resultBytes)
+		}
+	}
+
+	return nil, fmt.Errorf("unsupported CNI result version %q", version)
+}