invoke: Enable plugin file names with extensions

A CNI network configuration file contains the plugin's executable file name.
Some platforms like Windows require a file name extension for executables.
This causes unnecessary burden on admins as they now have to maintain two
versions of each type of netconfig file, which differ only by the ".exe"
extension. A much simpler design is for invoke package to also look for
well-known extensions on platforms that require it. Existing tests are
improved and new tests are added to cover the new behavior.

Fixes #360

invoke/find.go

@@ -30,18 +30,14 @@ func FindInPath(plugin string, paths []string) (string, error) {
 		return "", fmt.Errorf("no paths provided")
 	}
 
-	var fullpath string
 	for _, path := range paths {
-		full := filepath.Join(path, plugin)
-		if fi, err := os.Stat(full); err == nil && fi.Mode().IsRegular() {
-			fullpath = full
-			break
-		}
-	}
-
-	if fullpath == "" {
-		return "", fmt.Errorf("failed to find plugin %q in path %s", plugin, paths)
-	}
-
+		for _, fe := range ExecutableFileExtensions {
+			fullpath := filepath.Join(path, plugin) + fe
+			if fi, err := os.Stat(fullpath); err == nil && fi.Mode().IsRegular() {
 				return fullpath, nil
+			}
+		}
+	}
+
+	return "", fmt.Errorf("failed to find plugin %q in path %s", plugin, paths)
 }

invoke/find_test.go

@@ -17,7 +17,9 @@ package invoke_test
 import (
 	"fmt"
 	"io/ioutil"
+	"os"
 	"path/filepath"
+	"strings"
 
 	"github.com/containernetworking/cni/pkg/invoke"
 	. "github.com/onsi/ginkgo"
@@ -28,6 +30,8 @@ var _ = Describe("FindInPath", func() {
 	var (
 		multiplePaths         []string
 		pluginName            string
+		plugin2NameWithExt    string
+		plugin2NameWithoutExt string
 		pluginDir             string
 		anotherTempDir        string
 	)
@@ -37,11 +41,24 @@ var _ = Describe("FindInPath", func() {
 		Expect(err).NotTo(HaveOccurred())
 
 		plugin, err := ioutil.TempFile(tempDir, "a-cni-plugin")
+		Expect(err).NotTo(HaveOccurred())
+
+		plugin2Name := "a-plugin-with-extension" + invoke.ExecutableFileExtensions[0]
+		plugin2, err := os.Create(filepath.Join(tempDir, plugin2Name))
+		Expect(err).NotTo(HaveOccurred())
 
 		anotherTempDir, err = ioutil.TempDir("", "nothing-here")
+		Expect(err).NotTo(HaveOccurred())
 
 		multiplePaths = []string{anotherTempDir, tempDir}
 		pluginDir, pluginName = filepath.Split(plugin.Name())
+		_, plugin2NameWithExt = filepath.Split(plugin2.Name())
+		plugin2NameWithoutExt = strings.Split(plugin2NameWithExt, ".")[0]
+	})
+
+	AfterEach(func() {
+		os.RemoveAll(pluginDir)
+		os.RemoveAll(anotherTempDir)
 	})
 
 	Context("when multiple paths are provided", func() {
@@ -52,6 +69,14 @@ var _ = Describe("FindInPath", func() {
 		})
 	})
 
+	Context("when a plugin name without its file name extension is provided", func() {
+		It("returns the path to the plugin, including its extension", func() {
+			pluginPath, err := invoke.FindInPath(plugin2NameWithoutExt, multiplePaths)
+			Expect(err).NotTo(HaveOccurred())
+			Expect(pluginPath).To(Equal(filepath.Join(pluginDir, plugin2NameWithExt)))
+		})
+	})
+
 	Context("when an error occurs", func() {
 		Context("when no paths are provided", func() {
 			It("returns an error noting no paths were provided", func() {

invoke/os_unix.go

@@ -0,0 +1,20 @@
+// 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.
+
+// +build darwin dragonfly freebsd linux netbsd opensbd solaris
+
+package invoke
+
+// Valid file extensions for plugin executables.
+var ExecutableFileExtensions = []string{""}

invoke/os_windows.go

@@ -0,0 +1,18 @@
+// 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
+
+// Valid file extensions for plugin executables.
+var ExecutableFileExtensions = []string{".exe", ""}