invoke: correctly infer version for 0.1.0-vintage plugins

Older plugins return a known error when issued the VERSION command.
Capture this error and report it as a 0.1.0 version plugin.

invoke/exec.go

@@ -65,9 +65,19 @@ func (e *PluginExec) WithoutResult(pluginPath string, netconf []byte, args CNIAr
 }
 
 func (e *PluginExec) GetVersion(pluginPath string) (version.PluginInfo, error) {
-	args := &Args{Command: "VERSION"}
+	args := &Args{
+		Command: "VERSION",
+
+		// set fake values required by plugins built against an older version of skel
+		NetNS:  "/tmp/not/a/container",
+		IfName: "not-an-interface",
+		Path:   "/tmp/not/a/path",
+	}
 	stdoutBytes, err := e.RawExec.ExecPlugin(pluginPath, nil, args.AsEnv())
 	if err != nil {
+		if err.Error() == "unknown CNI_COMMAND: VERSION" {
+			return version.PluginSupports("0.1.0"), nil
+		}
 		return nil, err
 	}
 

invoke/exec_integration_test.go

@@ -0,0 +1,72 @@
+// 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 invoke_test
+
+import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
+
+	"github.com/containernetworking/cni/pkg/invoke"
+	"github.com/containernetworking/cni/pkg/version"
+	"github.com/containernetworking/cni/pkg/version/testhelpers"
+
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/ginkgo/extensions/table"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("GetVersion, integration tests", func() {
+	var (
+		pluginDir  string
+		pluginPath string
+	)
+
+	BeforeEach(func() {
+		pluginDir, err := ioutil.TempDir("", "plugins")
+		Expect(err).NotTo(HaveOccurred())
+		pluginPath = filepath.Join(pluginDir, "test-plugin")
+	})
+
+	AfterEach(func() {
+		Expect(os.RemoveAll(pluginDir)).To(Succeed())
+	})
+
+	DescribeTable("correctly reporting plugin versions",
+		func(gitRef string, pluginSource string, expectedVersions version.PluginInfo) {
+			Expect(testhelpers.BuildAt([]byte(pluginSource), gitRef, pluginPath)).To(Succeed())
+			versionInfo, err := invoke.ExecPluginForVersion(pluginPath)
+			Expect(err).NotTo(HaveOccurred())
+
+			Expect(versionInfo.SupportedVersions()).To(ConsistOf(expectedVersions.SupportedVersions()))
+		},
+		Entry("old plugin, before VERSION was introduced", git_ref_v010, plugin_source_v010, version.PluginSupports("0.1.0")),
+		Entry("when VERSION was introduced", git_ref_v020, plugin_source_v010, version.PluginSupports("0.1.0", "0.2.0")),
+	)
+})
+
+// a minimal 0.1.0 / 0.2.0 plugin
+const plugin_source_v010 = `package main
+
+import "github.com/containernetworking/cni/pkg/skel"
+import "fmt"
+
+func c(_ *skel.CmdArgs) error { fmt.Println("{}"); return nil }
+
+func main() { skel.PluginMain(c, c) }
+`
+
+const git_ref_v010 = "2c482f4"
+const git_ref_v020 = "349d66d"

invoke/exec_test.go

@@ -25,7 +25,7 @@ import (
 	. "github.com/onsi/gomega"
 )
 
-var _ = Describe("Executing a plugin", func() {
+var _ = Describe("Executing a plugin, unit tests", func() {
 	var (
 		pluginExec     *invoke.PluginExec
 		rawExec        *fakes.RawExec