Basic support for kubectl plugins

hack/make-rules/test-cmd-util.sh

@@ -3679,5 +3679,49 @@ __EOF__
     kube::test::get_object_assert csr "{{range.items}}{{$id_field}}{{end}}" ''
   fi
 
+  ###########
+  # Plugins #
+  ###########
+  kube::log::status "Testing kubectl plugins"
+
+  # single plugins path
+  output_message=$(KUBECTL_PLUGINS_PATH=test/fixtures/pkg/kubectl/plugins kubectl -h 2>&1)
+  kube::test::if_has_string "${output_message}" 'echo\s\+Echoes for test-cmd'
+  kube::test::if_has_string "${output_message}" 'get\s\+The wonderful new plugin-based get!'
+  kube::test::if_has_string "${output_message}" 'error\s\+The tremendous plugin that always fails!'
+  kube::test::if_has_not_string "${output_message}" 'The hello plugin'
+  kube::test::if_has_not_string "${output_message}" 'Incomplete plugin'
+
+  # when overriding existing command, both appear in help. TODO handle this to not register plugins that override existing cmd.
+  kube::test::if_has_string "${output_message}" 'get\s\+Display one or many resources'
+
+  # multiple plugins path
+  output_message=$(KUBECTL_PLUGINS_PATH=test/fixtures/pkg/kubectl/plugins/:test/fixtures/pkg/kubectl/plugins2/ kubectl -h 2>&1)
+  kube::test::if_has_string "${output_message}" 'echo\s\+Echoes for test-cmd'
+  kube::test::if_has_string "${output_message}" 'get\s\+The wonderful new plugin-based get!'
+  kube::test::if_has_string "${output_message}" 'error\s\+The tremendous plugin that always fails!'
+  kube::test::if_has_string "${output_message}" 'hello\s\+The hello plugin'
+  kube::test::if_has_not_string "${output_message}" 'Incomplete plugin'
+
+  # don't override existing commands
+  output_message=$(KUBECTL_PLUGINS_PATH=test/fixtures/pkg/kubectl/plugins/:test/fixtures/pkg/kubectl/plugins2/ kubectl get -h 2>&1)
+  kube::test::if_has_string "${output_message}" 'Display one or many resources'
+  kube::test::if_has_not_string "$output_message{output_message}" 'The wonderful new plugin-based get'
+
+  # plugin help
+  output_message=$(KUBECTL_PLUGINS_PATH=test/fixtures/pkg/kubectl/plugins/:test/fixtures/pkg/kubectl/plugins2/ kubectl hello -h 2>&1)
+  kube::test::if_has_string "${output_message}" 'The hello plugin is a new plugin used by test-cmd to test multiple plugin locations.'
+  kube::test::if_has_string "${output_message}" 'Usage:'
+
+  # run plugin
+  output_message=$(KUBECTL_PLUGINS_PATH=test/fixtures/pkg/kubectl/plugins/:test/fixtures/pkg/kubectl/plugins2/ kubectl hello 2>&1)
+  kube::test::if_has_string "${output_message}" '#hello#'
+  output_message=$(KUBECTL_PLUGINS_PATH=test/fixtures/pkg/kubectl/plugins/:test/fixtures/pkg/kubectl/plugins2/ kubectl echo 2>&1)
+  kube::test::if_has_string "${output_message}" 'This plugin works!'
+  output_message=$(! KUBECTL_PLUGINS_PATH=test/fixtures/pkg/kubectl/plugins/ kubectl hello 2>&1)
+  kube::test::if_has_string "${output_message}" 'unknown command'
+  output_message=$(! KUBECTL_PLUGINS_PATH=test/fixtures/pkg/kubectl/plugins/ kubectl error 2>&1)
+  kube::test::if_has_string "${output_message}" 'error: exit status 1'
+
   kube::test::clear_all
 }

pkg/kubectl/BUILD

@@ -190,6 +190,7 @@ filegroup(
         ":package-srcs",
         "//pkg/kubectl/cmd:all-srcs",
         "//pkg/kubectl/metricsutil:all-srcs",
+        "//pkg/kubectl/plugins:all-srcs",
         "//pkg/kubectl/resource:all-srcs",
         "//pkg/kubectl/testing:all-srcs",
     ],

pkg/kubectl/cmd/BUILD

@@ -51,6 +51,7 @@ go_library(
         "logs.go",
         "options.go",
         "patch.go",
+        "plugin.go",
         "portforward.go",
         "proxy.go",
         "replace.go",
@@ -93,6 +94,7 @@ go_library(
         "//pkg/kubectl/cmd/util:go_default_library",
         "//pkg/kubectl/cmd/util/editor:go_default_library",
         "//pkg/kubectl/metricsutil:go_default_library",
+        "//pkg/kubectl/plugins:go_default_library",
         "//pkg/kubectl/resource:go_default_library",
         "//pkg/kubelet/types:go_default_library",
         "//pkg/printers:go_default_library",
@@ -173,6 +175,7 @@ go_test(
         "label_test.go",
         "logs_test.go",
         "patch_test.go",
+        "plugin_test.go",
         "portforward_test.go",
         "replace_test.go",
         "rollingupdate_test.go",
@@ -207,6 +210,7 @@ go_test(
         "//pkg/kubectl:go_default_library",
         "//pkg/kubectl/cmd/testing:go_default_library",
         "//pkg/kubectl/cmd/util:go_default_library",
+        "//pkg/kubectl/plugins:go_default_library",
         "//pkg/kubectl/resource:go_default_library",
         "//pkg/printers:go_default_library",
         "//pkg/printers/internalversion:go_default_library",

pkg/kubectl/cmd/cmd.go

@@ -347,6 +347,24 @@ func NewKubectlCommand(f cmdutil.Factory, in io.Reader, out, err io.Writer) *cob
 			},
 		},
 	}
+
+	// Loads plugins and create commands for each plugin identified
+	loadedPlugins, loadErr := f.PluginLoader().Load()
+	if loadErr != nil {
+		glog.V(1).Infof("Unable to load plugins: %v", loadErr)
+	}
+	pluginRunner := f.PluginRunner()
+	if len(loadedPlugins) > 0 {
+		pluginCmds := []*cobra.Command{}
+		for _, p := range loadedPlugins {
+			pluginCmds = append(pluginCmds, NewCmdForPlugin(p, pluginRunner, in, out, err))
+		}
+		groups = append(groups, templates.CommandGroup{
+			Message:  "Plugins:",
+			Commands: pluginCmds,
+		})
+	}
+
 	groups.Add(cmds)
 
 	filters := []string{

pkg/kubectl/cmd/plugin.go

@@ -0,0 +1,54 @@
+/*
+Copyright 2017 The Kubernetes 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 cmd
+
+import (
+	"io"
+	"os"
+
+	"github.com/spf13/cobra"
+	"k8s.io/kubernetes/pkg/kubectl/cmd/templates"
+	cmdutil "k8s.io/kubernetes/pkg/kubectl/cmd/util"
+	"k8s.io/kubernetes/pkg/kubectl/plugins"
+)
+
+// NewCmdForPlugin creates a command capable of running the provided plugin.
+func NewCmdForPlugin(plugin *plugins.Plugin, runner plugins.PluginRunner, in io.Reader, out, errout io.Writer) *cobra.Command {
+	if !plugin.IsValid() {
+		return nil
+	}
+
+	return &cobra.Command{
+		Use:     plugin.Name,
+		Short:   plugin.ShortDesc,
+		Long:    templates.LongDesc(plugin.LongDesc),
+		Example: templates.Examples(plugin.Example),
+		Run: func(cmd *cobra.Command, args []string) {
+			ctx := plugins.RunningContext{
+				In:         in,
+				Out:        out,
+				ErrOut:     errout,
+				Args:       args,
+				Env:        os.Environ(),
+				WorkingDir: plugin.Dir,
+			}
+			if err := runner.Run(plugin, ctx); err != nil {
+				cmdutil.CheckErr(err)
+			}
+		},
+	}
+}

pkg/kubectl/cmd/plugin_test.go

@@ -0,0 +1,111 @@
+/*
+Copyright 2017 The Kubernetes 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 cmd
+
+import (
+	"bytes"
+	"fmt"
+	"testing"
+
+	cmdutil "k8s.io/kubernetes/pkg/kubectl/cmd/util"
+	"k8s.io/kubernetes/pkg/kubectl/plugins"
+)
+
+type mockPluginRunner struct {
+	success bool
+}
+
+func (r *mockPluginRunner) Run(p *plugins.Plugin, ctx plugins.RunningContext) error {
+	if !r.success {
+		return fmt.Errorf("oops %s", p.Name)
+	}
+	ctx.Out.Write([]byte(fmt.Sprintf("ok: %s", p.Name)))
+	return nil
+}
+
+func TestPluginCmd(t *testing.T) {
+	tests := []struct {
+		name            string
+		plugin          *plugins.Plugin
+		expectedSuccess bool
+		expectedNilCmd  bool
+	}{
+		{
+			name: "success",
+			plugin: &plugins.Plugin{
+				Description: plugins.Description{
+					Name:      "success",
+					ShortDesc: "The Test Plugin",
+					Command:   "echo ok",
+				},
+			},
+			expectedSuccess: true,
+		},
+		{
+			name: "incomplete",
+			plugin: &plugins.Plugin{
+				Description: plugins.Description{
+					Name:      "incomplete",
+					ShortDesc: "The Incomplete Plugin",
+				},
+			},
+			expectedNilCmd: true,
+		},
+		{
+			name: "failure",
+			plugin: &plugins.Plugin{
+				Description: plugins.Description{
+					Name:      "failure",
+					ShortDesc: "The Failing Plugin",
+					Command:   "false",
+				},
+			},
+			expectedSuccess: false,
+		},
+	}
+
+	for _, test := range tests {
+		inBuf := bytes.NewBuffer([]byte{})
+		outBuf := bytes.NewBuffer([]byte{})
+		errBuf := bytes.NewBuffer([]byte{})
+
+		cmdutil.BehaviorOnFatal(func(str string, code int) {
+			errBuf.Write([]byte(str))
+		})
+
+		runner := &mockPluginRunner{
+			success: test.expectedSuccess,
+		}
+
+		cmd := NewCmdForPlugin(test.plugin, runner, inBuf, outBuf, errBuf)
+		if cmd == nil {
+			if !test.expectedNilCmd {
+				t.Fatalf("%s: command was unexpectedly not registered", test.name)
+			}
+			continue
+		}
+		cmd.Run(cmd, []string{})
+
+		if test.expectedSuccess && outBuf.String() != fmt.Sprintf("ok: %s", test.plugin.Name) {
+			t.Errorf("%s: unexpected output: %q", test.name, outBuf.String())
+		}
+
+		if !test.expectedSuccess && errBuf.String() != fmt.Sprintf("error: oops %s", test.plugin.Name) {
+			t.Errorf("%s: unexpected err output: %q", test.name, errBuf.String())
+		}
+	}
+}

pkg/kubectl/cmd/templates/normalizers.go

@@ -28,11 +28,17 @@ const Indentation = `  `
 
 // LongDesc normalizes a command's long description to follow the conventions.
 func LongDesc(s string) string {
+	if len(s) == 0 {
+		return s
+	}
 	return normalizer{s}.heredoc().markdown().trim().string
 }
 
 // Examples normalizes a command's examples to follow the conventions.
 func Examples(s string) string {
+	if len(s) == 0 {
+		return s
+	}
 	return normalizer{s}.trim().indent().string
 }
 

pkg/kubectl/cmd/testing/BUILD

@@ -20,6 +20,7 @@ go_library(
         "//pkg/kubectl:go_default_library",
         "//pkg/kubectl/cmd/util:go_default_library",
         "//pkg/kubectl/cmd/util/openapi:go_default_library",
+        "//pkg/kubectl/plugins:go_default_library",
         "//pkg/kubectl/resource:go_default_library",
         "//pkg/printers:go_default_library",
         "//vendor/github.com/emicklei/go-restful/swagger:go_default_library",

pkg/kubectl/cmd/testing/fake.go

@@ -43,6 +43,7 @@ import (
 	"k8s.io/kubernetes/pkg/kubectl"
 	cmdutil "k8s.io/kubernetes/pkg/kubectl/cmd/util"
 	"k8s.io/kubernetes/pkg/kubectl/cmd/util/openapi"
+	"k8s.io/kubernetes/pkg/kubectl/plugins"
 	"k8s.io/kubernetes/pkg/kubectl/resource"
 	"k8s.io/kubernetes/pkg/printers"
 )
@@ -481,6 +482,14 @@ func (f *FakeFactory) SuggestedPodTemplateResources() []schema.GroupResource {
 	return []schema.GroupResource{}
 }
 
+func (f *FakeFactory) PluginLoader() plugins.PluginLoader {
+	return &plugins.DummyPluginLoader{}
+}
+
+func (f *FakeFactory) PluginRunner() plugins.PluginRunner {
+	return &plugins.ExecPluginRunner{}
+}
+
 type fakeMixedFactory struct {
 	cmdutil.Factory
 	tf        *TestFactory

pkg/kubectl/cmd/util/BUILD

@@ -38,6 +38,7 @@ go_library(
         "//pkg/controller:go_default_library",
         "//pkg/kubectl:go_default_library",
         "//pkg/kubectl/cmd/util/openapi:go_default_library",
+        "//pkg/kubectl/plugins:go_default_library",
         "//pkg/kubectl/resource:go_default_library",
         "//pkg/printers:go_default_library",
         "//pkg/printers/internalversion:go_default_library",

pkg/kubectl/cmd/util/factory.go

@@ -52,6 +52,7 @@ import (
 	coreclient "k8s.io/kubernetes/pkg/client/clientset_generated/internalclientset/typed/core/internalversion"
 	"k8s.io/kubernetes/pkg/kubectl"
 	"k8s.io/kubernetes/pkg/kubectl/cmd/util/openapi"
+	"k8s.io/kubernetes/pkg/kubectl/plugins"
 	"k8s.io/kubernetes/pkg/kubectl/resource"
 	"k8s.io/kubernetes/pkg/printers"
 )
@@ -240,6 +241,10 @@ type BuilderFactory interface {
 	PrintObject(cmd *cobra.Command, mapper meta.RESTMapper, obj runtime.Object, out io.Writer) error
 	// One stop shopping for a Builder
 	NewBuilder() *resource.Builder
+	// PluginLoader provides the implementation to be used to load cli plugins.
+	PluginLoader() plugins.PluginLoader
+	// PluginRunner provides the implementation to be used to run cli plugins.
+	PluginRunner() plugins.PluginRunner
 }
 
 func getGroupVersionKinds(gvks []schema.GroupVersionKind, group string) []schema.GroupVersionKind {

pkg/kubectl/cmd/util/factory_builder.go

@@ -21,12 +21,14 @@ package util
 import (
 	"fmt"
 	"io"
+	"os"
 
 	"github.com/spf13/cobra"
 
 	"k8s.io/apimachinery/pkg/api/meta"
 	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
 	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/kubernetes/pkg/kubectl/plugins"
 	"k8s.io/kubernetes/pkg/kubectl/resource"
 	"k8s.io/kubernetes/pkg/printers"
 )
@@ -130,3 +132,22 @@ func (f *ring2Factory) NewBuilder() *resource.Builder {
 
 	return resource.NewBuilder(mapper, categoryExpander, typer, resource.ClientMapperFunc(f.objectMappingFactory.ClientForMapping), f.clientAccessFactory.Decoder(true))
 }
+
+// PluginLoader loads plugins from a path set by the KUBECTL_PLUGINS_PATH env var.
+// If this env var is not set, it defaults to
+//   "~/.kube/plugins", plus
+//  "./kubectl/plugins" directory under the "data dir" directory specified by the XDG
+// system directory structure spec for the given platform.
+func (f *ring2Factory) PluginLoader() plugins.PluginLoader {
+	if len(os.Getenv("KUBECTL_PLUGINS_PATH")) > 0 {
+		return plugins.PluginsEnvVarPluginLoader()
+	}
+	return plugins.TolerantMultiPluginLoader{
+		plugins.XDGDataPluginLoader(),
+		plugins.UserDirPluginLoader(),
+	}
+}
+
+func (f *ring2Factory) PluginRunner() plugins.PluginRunner {
+	return &plugins.ExecPluginRunner{}
+}

pkg/kubectl/plugins/BUILD

@@ -0,0 +1,48 @@
+package(default_visibility = ["//visibility:public"])
+
+licenses(["notice"])
+
+load(
+    "@io_bazel_rules_go//go:def.bzl",
+    "go_library",
+    "go_test",
+)
+
+go_library(
+    name = "go_default_library",
+    srcs = [
+        "loader.go",
+        "plugins.go",
+        "runner.go",
+    ],
+    tags = ["automanaged"],
+    deps = [
+        "//vendor/github.com/ghodss/yaml:go_default_library",
+        "//vendor/github.com/golang/glog:go_default_library",
+        "//vendor/k8s.io/client-go/tools/clientcmd:go_default_library",
+    ],
+)
+
+filegroup(
+    name = "package-srcs",
+    srcs = glob(["**"]),
+    tags = ["automanaged"],
+    visibility = ["//visibility:private"],
+)
+
+filegroup(
+    name = "all-srcs",
+    srcs = [":package-srcs"],
+    tags = ["automanaged"],
+)
+
+go_test(
+    name = "go_default_test",
+    srcs = [
+        "loader_test.go",
+        "plugins_test.go",
+        "runner_test.go",
+    ],
+    library = ":go_default_library",
+    tags = ["automanaged"],
+)

pkg/kubectl/plugins/examples/aging/aging.rb

@@ -0,0 +1,69 @@
+#!/usr/bin/env ruby
+
+require 'json'
+require 'date'
+
+class Numeric
+  def duration
+    secs  = self.to_int
+    mins  = secs / 60
+    hours = mins / 60
+    days  = hours / 24
+
+    if days > 0
+      "#{days} days and #{hours % 24} hours"
+    elsif hours > 0
+      "#{hours} hours and #{mins % 60} minutes"
+    elsif mins > 0
+      "#{mins} minutes and #{secs % 60} seconds"
+    elsif secs >= 0
+      "#{secs} seconds"
+    end
+  end
+end
+
+pods_json = `kubectl get pods -o json`
+pods_parsed = JSON.parse(pods_json)
+
+puts "The Magnificent Aging Plugin."
+
+data = Hash.new
+max_name_length = 0
+max_age = 0
+min_age = 0
+
+pods_parsed['items'].each { |pod|
+  name = pod['metadata']['name']
+  creation = pod['metadata']['creationTimestamp']
+
+  age = Time.now - DateTime.parse(creation).to_time
+  data[name] = age
+
+  if name.length > max_name_length
+    max_name_length = name.length
+  end
+  if age > max_age
+    max_age = age
+  end
+  if age < min_age
+    min_age = age
+  end
+} 
+
+data = data.sort_by{ |name, age| age }
+
+if data.length > 0
+  puts ""
+  data.each { |name, age|
+    output = ""
+    output += name.rjust(max_name_length, ' ') + ": "
+    bar_size = (age*80/max_age).ceil 
+    bar_size.times{ output += "▒" }
+    output += " " + age.duration
+    puts output
+    puts ""
+  }
+else
+  puts "No pods"
+end
+

pkg/kubectl/plugins/examples/aging/plugin.yaml

@@ -0,0 +1,8 @@
+name: "aging"
+shortDesc: "Aging shows pods by age"
+longDesc: >
+  Aging shows pods from the current namespace by age.
+  Once we have plugin support for global flags through 
+  env vars (planned for V1) we'll be able to switch
+  between namespaces using the --namespace flag.
+command: ./aging.rb

pkg/kubectl/plugins/examples/hello/plugin.yaml

@@ -0,0 +1,3 @@
+name: "hello"
+shortDesc: "I say hello!"
+command: "echo Hello plugins!"

pkg/kubectl/plugins/loader.go

@@ -0,0 +1,192 @@
+/*
+Copyright 2017 The Kubernetes 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 plugins
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+
+	"github.com/ghodss/yaml"
+	"github.com/golang/glog"
+
+	"k8s.io/client-go/tools/clientcmd"
+)
+
+const PluginDescriptorFilename = "plugin.yaml"
+
+// PluginLoader is capable of loading a list of plugin descriptions.
+type PluginLoader interface {
+	Load() (Plugins, error)
+}
+
+// DirectoryPluginLoader is a PluginLoader that loads plugin descriptions
+// from a given directory in the filesystem. Plugins are located in subdirs
+// under the loader "root", where each subdir must contain, at least, a plugin
+// descriptor file called "plugin.yaml" that translates into a PluginDescription.
+type DirectoryPluginLoader struct {
+	Directory string
+}
+
+// Load reads the directory the loader holds and loads plugin descriptions.
+func (l *DirectoryPluginLoader) Load() (Plugins, error) {
+	if len(l.Directory) == 0 {
+		return nil, fmt.Errorf("directory not specified")
+	}
+
+	list := Plugins{}
+
+	stat, err := os.Stat(l.Directory)
+	if err != nil {
+		return nil, err
+	}
+	if !stat.IsDir() {
+		return nil, fmt.Errorf("not a directory: %s", l.Directory)
+	}
+
+	base, err := filepath.Abs(l.Directory)
+	if err != nil {
+		return nil, err
+	}
+
+	// read the base directory tree searching for plugin descriptors
+	// fails silently (descriptors unable to be read or unmarshalled are logged but skipped)
+	err = filepath.Walk(base, func(path string, fileInfo os.FileInfo, walkErr error) error {
+		if fileInfo.IsDir() || fileInfo.Name() != PluginDescriptorFilename || walkErr != nil {
+			return nil
+		}
+
+		file, err := ioutil.ReadFile(path)
+		if err != nil {
+			glog.V(1).Infof("Unable to read plugin descriptor %s: %v", path, err)
+			return nil
+		}
+
+		plugin := &Plugin{}
+		if err := yaml.Unmarshal(file, plugin); err != nil {
+			glog.V(1).Infof("Unable to unmarshal plugin descriptor %s: %v", path, err)
+			return nil
+		}
+
+		if err := plugin.Validate(); err != nil {
+			glog.V(1).Infof("%v", err)
+			return nil
+		}
+
+		plugin.Dir = filepath.Dir(path)
+		plugin.DescriptorName = fileInfo.Name()
+
+		glog.V(6).Infof("Plugin loaded: %s", plugin.Name)
+		list = append(list, plugin)
+
+		return nil
+	})
+
+	return list, err
+}
+
+// UserDirPluginLoader is a PluginLoader that loads plugins from the
+// "plugins" directory under the user's kubeconfig dir (usually "~/.kube/plugins/").
+func UserDirPluginLoader() PluginLoader {
+	dir := filepath.Join(clientcmd.RecommendedConfigDir, "plugins")
+	return &DirectoryPluginLoader{
+		Directory: dir,
+	}
+}
+
+// PathFromEnvVarPluginLoader is a PluginLoader that loads plugins from one or more
+// directories specified by the provided env var name. In case the env var is not
+// set, the PluginLoader just loads nothing. A list of subdirectories can be provided,
+// which will be appended to each path specified by the env var.
+func PathFromEnvVarPluginLoader(envVarName string, subdirs ...string) PluginLoader {
+	env := os.Getenv(envVarName)
+	if len(env) == 0 {
+		return &DummyPluginLoader{}
+	}
+	loader := MultiPluginLoader{}
+	for _, path := range filepath.SplitList(env) {
+		dir := append([]string{path}, subdirs...)
+		loader = append(loader, &DirectoryPluginLoader{
+			Directory: filepath.Join(dir...),
+		})
+	}
+	return loader
+}
+
+// PluginsEnvVarPluginLoader is a PluginLoader that loads plugins from one or more
+// directories specified by the KUBECTL_PLUGINS_PATH env var.
+func PluginsEnvVarPluginLoader() PluginLoader {
+	return PathFromEnvVarPluginLoader("KUBECTL_PLUGINS_PATH")
+}
+
+// XDGDataPluginLoader is a PluginLoader that loads plugins from one or more
+// directories specified by the XDG system directory structure spec in the
+// XDG_DATA_DIRS env var, plus the "kubectl/plugins/" suffix. According to the
+// spec, if XDG_DATA_DIRS is not set it defaults to "/usr/local/share:/usr/share".
+func XDGDataPluginLoader() PluginLoader {
+	envVarName := "XDG_DATA_DIRS"
+	if len(os.Getenv(envVarName)) > 0 {
+		return PathFromEnvVarPluginLoader(envVarName, "kubectl", "plugins")
+	}
+	return TolerantMultiPluginLoader{
+		&DirectoryPluginLoader{
+			Directory: "/usr/local/share",
+		},
+		&DirectoryPluginLoader{
+			Directory: "/usr/share",
+		},
+	}
+}
+
+// MultiPluginLoader is a PluginLoader that can encapsulate multiple plugin loaders,
+// a successful loading means every encapsulated loader was able to load without errors.
+type MultiPluginLoader []PluginLoader
+
+func (l MultiPluginLoader) Load() (Plugins, error) {
+	plugins := Plugins{}
+	for _, loader := range l {
+		loaded, err := loader.Load()
+		if err != nil {
+			return nil, err
+		}
+		plugins = append(plugins, loaded...)
+	}
+	return plugins, nil
+}
+
+// TolerantMultiPluginLoader is a PluginLoader than encapsulates multiple plugins loaders,
+// but is tolerant to errors while loading from them.
+type TolerantMultiPluginLoader []PluginLoader
+
+func (l TolerantMultiPluginLoader) Load() (Plugins, error) {
+	plugins := Plugins{}
+	for _, loader := range l {
+		loaded, _ := loader.Load()
+		if loaded != nil {
+			plugins = append(plugins, loaded...)
+		}
+	}
+	return plugins, nil
+}
+
+// DummyPluginLoader loads nothing.
+type DummyPluginLoader struct{}
+
+func (l *DummyPluginLoader) Load() (Plugins, error) {
+	return Plugins{}, nil
+}

pkg/kubectl/plugins/loader_test.go

@@ -0,0 +1,197 @@
+/*
+Copyright 2017 The Kubernetes 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 plugins
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strings"
+	"testing"
+)
+
+func TestSuccessfulDirectoryPluginLoader(t *testing.T) {
+	tmp, err := setupValidPlugins(3)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	defer os.RemoveAll(tmp)
+
+	loader := &DirectoryPluginLoader{
+		Directory: tmp,
+	}
+	plugins, err := loader.Load()
+	if err != nil {
+		t.Errorf("Unexpected error loading plugins: %v", err)
+	}
+
+	if count := len(plugins); count != 3 {
+		t.Errorf("Unexpected number of loaded plugins, wanted 3, got %d", count)
+	}
+
+	for _, plugin := range plugins {
+		if m, _ := regexp.MatchString("^plugin[123]$", plugin.Name); !m {
+			t.Errorf("Unexpected plugin name %s", plugin.Name)
+		}
+		if m, _ := regexp.MatchString("^The plugin[123] test plugin$", plugin.ShortDesc); !m {
+			t.Errorf("Unexpected plugin short desc %s", plugin.ShortDesc)
+		}
+		if m, _ := regexp.MatchString("^echo plugin[123]$", plugin.Command); !m {
+			t.Errorf("Unexpected plugin command %s", plugin.Command)
+		}
+	}
+}
+
+func TestEmptyDirectoryPluginLoader(t *testing.T) {
+	loader := &DirectoryPluginLoader{}
+	_, err := loader.Load()
+	if err == nil {
+		t.Errorf("Expected error, got none")
+	}
+	if m, _ := regexp.MatchString("^directory not specified$", err.Error()); !m {
+		t.Errorf("Unexpected error %v", err)
+	}
+}
+
+func TestNotDirectoryPluginLoader(t *testing.T) {
+	tmp, err := ioutil.TempDir("", "")
+	if err != nil {
+		t.Fatalf("unexpected ioutil.TempDir error: %v", err)
+	}
+	defer os.RemoveAll(tmp)
+
+	file := filepath.Join(tmp, "test.tmp")
+	if err := ioutil.WriteFile(file, []byte("test"), 644); err != nil {
+		t.Fatalf("unexpected ioutil.WriteFile error: %v", err)
+	}
+
+	loader := &DirectoryPluginLoader{
+		Directory: file,
+	}
+	_, err = loader.Load()
+	if err == nil {
+		t.Errorf("Expected error, got none")
+	}
+	if !strings.Contains(err.Error(), "not a directory") {
+		t.Errorf("Unexpected error %v", err)
+	}
+}
+
+func TestUnexistentDirectoryPluginLoader(t *testing.T) {
+	loader := &DirectoryPluginLoader{
+		Directory: "/hopefully-does-not-exist",
+	}
+	_, err := loader.Load()
+	if err == nil {
+		t.Errorf("Expected error, got none")
+	}
+	if !strings.Contains(err.Error(), "no such file or directory") {
+		t.Errorf("Unexpected error %v", err)
+	}
+}
+
+func TestPluginsEnvVarPluginLoader(t *testing.T) {
+	tmp, err := setupValidPlugins(1)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	defer os.RemoveAll(tmp)
+
+	env := "KUBECTL_PLUGINS_PATH"
+	os.Setenv(env, tmp)
+	defer os.Unsetenv(env)
+
+	loader := PluginsEnvVarPluginLoader()
+
+	plugins, err := loader.Load()
+	if err != nil {
+		t.Errorf("Unexpected error loading plugins: %v", err)
+	}
+
+	if count := len(plugins); count != 1 {
+		t.Errorf("Unexpected number of loaded plugins, wanted 1, got %d", count)
+	}
+
+	plugin := plugins[0]
+	if "plugin1" != plugin.Name {
+		t.Errorf("Unexpected plugin name %s", plugin.Name)
+	}
+	if "The plugin1 test plugin" != plugin.ShortDesc {
+		t.Errorf("Unexpected plugin short desc %s", plugin.ShortDesc)
+	}
+	if "echo plugin1" != plugin.Command {
+		t.Errorf("Unexpected plugin command %s", plugin.Command)
+	}
+}
+
+func TestIncompletePluginDescriptor(t *testing.T) {
+	tmp, err := ioutil.TempDir("", "")
+	if err != nil {
+		t.Fatalf("unexpected ioutil.TempDir error: %v", err)
+	}
+
+	descriptor := `
+name: incomplete
+shortDesc: The incomplete test plugin`
+
+	if err := os.Mkdir(filepath.Join(tmp, "incomplete"), 0755); err != nil {
+		t.Fatalf("unexpected os.Mkdir error: %v", err)
+	}
+	if err := ioutil.WriteFile(filepath.Join(tmp, "incomplete", "plugin.yaml"), []byte(descriptor), 0644); err != nil {
+		t.Fatalf("unexpected ioutil.WriteFile error: %v", err)
+	}
+
+	defer os.RemoveAll(tmp)
+
+	loader := &DirectoryPluginLoader{
+		Directory: tmp,
+	}
+	plugins, err := loader.Load()
+	if err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+
+	if count := len(plugins); count != 0 {
+		t.Errorf("Unexpected number of loaded plugins, wanted 0, got %d", count)
+	}
+}
+
+func setupValidPlugins(count int) (string, error) {
+	tmp, err := ioutil.TempDir("", "")
+	if err != nil {
+		return "", fmt.Errorf("unexpected ioutil.TempDir error: %v", err)
+	}
+
+	for i := 1; i <= count; i++ {
+		name := fmt.Sprintf("plugin%d", i)
+		descriptor := fmt.Sprintf(`
+name: %[1]s
+shortDesc: The %[1]s test plugin
+command: echo %[1]s`, name)
+
+		if err := os.Mkdir(filepath.Join(tmp, name), 0755); err != nil {
+			return "", fmt.Errorf("unexpected os.Mkdir error: %v", err)
+		}
+		if err := ioutil.WriteFile(filepath.Join(tmp, name, "plugin.yaml"), []byte(descriptor), 0644); err != nil {
+			return "", fmt.Errorf("unexpected ioutil.WriteFile error: %v", err)
+		}
+	}
+
+	return tmp, nil
+}

pkg/kubectl/plugins/plugins.go

@@ -0,0 +1,58 @@
+/*
+Copyright 2017 The Kubernetes 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 plugins
+
+import "fmt"
+
+// Plugin is the representation of a CLI extension (plugin).
+type Plugin struct {
+	Description
+	Source
+	Context RunningContext `json:"-"`
+}
+
+// PluginDescription holds everything needed to register a
+// plugin as a command. Usually comes from a descriptor file.
+type Description struct {
+	Name      string `json:"name"`
+	ShortDesc string `json:"shortDesc"`
+	LongDesc  string `json:"longDesc,omitempty"`
+	Example   string `json:"example,omitempty"`
+	Command   string `json:"command"`
+}
+
+// PluginSource holds the location of a given plugin in the filesystem.
+type Source struct {
+	Dir            string `json:"-"`
+	DescriptorName string `json:"-"`
+}
+
+var IncompleteError = fmt.Errorf("incomplete plugin descriptor: name, shortDesc and command fields are required")
+
+func (p Plugin) Validate() error {
+	if len(p.Name) == 0 || len(p.ShortDesc) == 0 || len(p.Command) == 0 {
+		return IncompleteError
+	}
+	return nil
+}
+
+func (p Plugin) IsValid() bool {
+	return p.Validate() == nil
+}
+
+// Plugins is a list of plugins.
+type Plugins []*Plugin

pkg/kubectl/plugins/plugins_test.go

@@ -0,0 +1,70 @@
+/*
+Copyright 2017 The Kubernetes 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 plugins
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestPlugin(t *testing.T) {
+	tests := []struct {
+		plugin        Plugin
+		expectedErr   string
+		expectedValid bool
+	}{
+		{
+			plugin: Plugin{
+				Description: Description{
+					Name:      "test",
+					ShortDesc: "The test",
+					Command:   "echo 1",
+				},
+			},
+			expectedValid: true,
+		},
+		{
+			plugin: Plugin{
+				Description: Description{
+					Name:      "test",
+					ShortDesc: "The test",
+				},
+			},
+			expectedErr: "incomplete",
+		},
+		{
+			plugin:      Plugin{},
+			expectedErr: "incomplete",
+		},
+	}
+
+	for _, test := range tests {
+		if is := test.plugin.IsValid(); test.expectedValid != is {
+			t.Errorf("%s: expected valid=%v, got %v", test.plugin.Name, test.expectedValid, is)
+		}
+		err := test.plugin.Validate()
+		if len(test.expectedErr) > 0 {
+			if err == nil {
+				t.Errorf("%s: expected error, got none", test.plugin.Name)
+			} else if !strings.Contains(err.Error(), test.expectedErr) {
+				t.Errorf("%s: expected error containing %q, got %v", test.plugin.Name, test.expectedErr, err)
+			}
+		} else if err != nil {
+			t.Errorf("%s: expected no error, got %v", test.plugin.Name, err)
+		}
+	}
+}

pkg/kubectl/plugins/runner.go

@@ -0,0 +1,69 @@
+/*
+Copyright 2017 The Kubernetes 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 plugins
+
+import (
+	"io"
+	"os/exec"
+	"strings"
+
+	"github.com/golang/glog"
+)
+
+// PluginRunner is capable of running a plugin in a given running context.
+type PluginRunner interface {
+	Run(plugin *Plugin, ctx RunningContext) error
+}
+
+// RunningContext holds the context in which a given plugin is running - the
+// in, out, and err streams, arguments and environment passed to it, and the
+// working directory.
+type RunningContext struct {
+	In         io.Reader
+	Out        io.Writer
+	ErrOut     io.Writer
+	Args       []string
+	Env        []string
+	WorkingDir string
+}
+
+// ExecPluginRunner is a PluginRunner that uses Go's os/exec to run plugins.
+type ExecPluginRunner struct{}
+
+// Run takes a given plugin and runs it in a given context using os/exec, returning
+// any error found while running.
+func (r *ExecPluginRunner) Run(plugin *Plugin, ctx RunningContext) error {
+	command := strings.Split(plugin.Command, " ")
+	base := command[0]
+	args := []string{}
+	if len(command) > 1 {
+		args = command[1:]
+	}
+	args = append(args, ctx.Args...)
+
+	cmd := exec.Command(base, args...)
+
+	cmd.Stdin = ctx.In
+	cmd.Stdout = ctx.Out
+	cmd.Stderr = ctx.ErrOut
+
+	cmd.Env = ctx.Env
+	cmd.Dir = ctx.WorkingDir
+
+	glog.V(9).Infof("Running plugin %q as base command %q with args %v", plugin.Name, base, args)
+	return cmd.Run()
+}

pkg/kubectl/plugins/runner_test.go

@@ -0,0 +1,71 @@
+/*
+Copyright 2017 The Kubernetes 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 plugins
+
+import (
+	"bytes"
+	"testing"
+)
+
+func TestExecRunner(t *testing.T) {
+	tests := []struct {
+		name        string
+		command     string
+		expectedMsg string
+		expectedErr string
+	}{
+		{
+			name:        "success",
+			command:     "echo test ok",
+			expectedMsg: "test ok\n",
+		},
+		{
+			name:        "invalid",
+			command:     "false",
+			expectedErr: "exit status 1",
+		},
+	}
+
+	for _, test := range tests {
+		outBuf := bytes.NewBuffer([]byte{})
+
+		plugin := &Plugin{
+			Description: Description{
+				Name:      test.name,
+				ShortDesc: "Test Runner Plugin",
+				Command:   test.command,
+			},
+		}
+
+		ctx := RunningContext{
+			Out:        outBuf,
+			WorkingDir: ".",
+		}
+
+		runner := &ExecPluginRunner{}
+		err := runner.Run(plugin, ctx)
+
+		if outBuf.String() != test.expectedMsg {
+			t.Errorf("%s: unexpected output: %q", test.name, outBuf.String())
+		}
+
+		if err != nil && err.Error() != test.expectedErr {
+			t.Errorf("%s: unexpected err output: %v", test.name, err)
+		}
+	}
+
+}

staging/src/k8s.io/client-go/tools/clientcmd/loader.go

@@ -47,8 +47,11 @@ const (
 	RecommendedSchemaName       = "schema"
 )
 
-var RecommendedHomeFile = path.Join(homedir.HomeDir(), RecommendedHomeDir, RecommendedFileName)
+var (
-var RecommendedSchemaFile = path.Join(homedir.HomeDir(), RecommendedHomeDir, RecommendedSchemaName)
+	RecommendedConfigDir  = path.Join(homedir.HomeDir(), RecommendedHomeDir)
+	RecommendedHomeFile   = path.Join(RecommendedConfigDir, RecommendedFileName)
+	RecommendedSchemaFile = path.Join(RecommendedConfigDir, RecommendedSchemaName)
+)
 
 // currentMigrationRules returns a map that holds the history of recommended home directories used in previous versions.
 // Any future changes to RecommendedHomeFile and related are expected to add a migration rule here, in order to make

test/fixtures/pkg/kubectl/plugins/echo/plugin.yaml

@@ -0,0 +1,4 @@
+name: "echo"
+shortDesc: "Echoes for test-cmd"
+longDesc: "Long description for the test-cmd echo plugin"
+command: "echo This plugin works!"

test/fixtures/pkg/kubectl/plugins/error/plugin.yaml

@@ -0,0 +1,3 @@
+name: "error"
+shortDesc: "The tremendous plugin that always fails!"
+command: "false"

test/fixtures/pkg/kubectl/plugins/get/plugin.yaml

@@ -0,0 +1,3 @@
+name: "get"
+shortDesc: "The wonderful new plugin-based get!"
+command: "echo new-get"

test/fixtures/pkg/kubectl/plugins/incomplete/plugin.yaml

@@ -0,0 +1,2 @@
+name: "incomplete"
+shortDesc: "Incomplete plugin"

test/fixtures/pkg/kubectl/plugins2/hello/hello.sh

@@ -0,0 +1,19 @@
+#!/bin/bash
+
+# Copyright 2017 The Kubernetes 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.
+
+echo "#######"
+echo "#hello#"
+echo "#######"

test/fixtures/pkg/kubectl/plugins2/hello/plugin.yaml

@@ -0,0 +1,7 @@
+name: hello
+shortDesc: "The hello plugin"
+longDesc: >
+  The hello plugin is a new
+  plugin used by test-cmd
+  to test multiple plugin locations.
+command: ./hello.sh