versioning: plugins report a list of supported versions

Further progress on versioning support (Issue #266).
Bump CNI spec version to 0.3.0

libcni/api.go

@@ -19,6 +19,7 @@ import (
 
 	"github.com/containernetworking/cni/pkg/invoke"
 	"github.com/containernetworking/cni/pkg/types"
+	"github.com/containernetworking/cni/pkg/version"
 )
 
 type RuntimeConf struct {
@@ -60,6 +61,17 @@ func (c *CNIConfig) DelNetwork(net *NetworkConfig, rt *RuntimeConf) error {
 	return invoke.ExecPluginWithoutResult(pluginPath, net.Bytes, c.args("DEL", rt))
 }
 
+func (c *CNIConfig) GetVersionInfo(pluginType string) (version.PluginInfo, error) {
+	pluginPath, err := invoke.FindInPath(pluginType, c.Path)
+	if err != nil {
+		return nil, err
+	}
+
+	// TODO: if error is because plugin is old and VERSION command is unrecognized
+	// then do the right thing and return version.PluginSupports("0.1.0"), nil
+	return invoke.ExecPluginForVersion(pluginPath)
+}
+
 // =====
 func (c *CNIConfig) args(action string, rt *RuntimeConf) *invoke.Args {
 	return &invoke.Args{

libcni/api_test.go

@@ -155,4 +155,23 @@ var _ = Describe("Invoking the plugin", func() {
 			})
 		})
 	})
+
+	Describe("GetVersionInfo", func() {
+		It("executes the plugin with the command VERSION", func() {
+			versionInfo, err := cniConfig.GetVersionInfo("noop")
+			Expect(err).NotTo(HaveOccurred())
+
+			Expect(versionInfo).NotTo(BeNil())
+			Expect(versionInfo.SupportedVersions()).To(Equal([]string{
+				"0.-42.0", "0.1.0", "0.2.0", "0.3.0",
+			}))
+		})
+
+		Context("when finding the plugin fails", func() {
+			It("returns the error", func() {
+				_, err := cniConfig.GetVersionInfo("does-not-exist")
+				Expect(err).To(MatchError(ContainSubstring(`failed to find plugin "does-not-exist"`)))
+			})
+		})
+	})
 })