allow re-usability of plugin handler, allow support for multiple valid plugin filename prefixes

pkg/kubectl/cmd/cmd.go

@@ -293,7 +293,7 @@ var (
 
 // NewDefaultKubectlCommand creates the `kubectl` command with default arguments
 func NewDefaultKubectlCommand() *cobra.Command {
-	return NewDefaultKubectlCommandWithArgs(&defaultPluginHandler{}, os.Args, os.Stdin, os.Stdout, os.Stderr)
+	return NewDefaultKubectlCommandWithArgs(NewDefaultPluginHandler(plugin.ValidPluginFilenamePrefixes), os.Args, os.Stdin, os.Stdout, os.Stderr)
 }
 
 // NewDefaultKubectlCommandWithArgs creates the `kubectl` command with arguments
@@ -310,7 +310,7 @@ func NewDefaultKubectlCommandWithArgs(pluginHandler PluginHandler, args []string
 		// only look for suitable extension executables if
 		// the specified command does not already exist
 		if _, _, err := cmd.Find(cmdPathPieces); err != nil {
-			if err := handleEndpointExtensions(pluginHandler, cmdPathPieces); err != nil {
+			if err := HandlePluginCommand(pluginHandler, cmdPathPieces); err != nil {
 				fmt.Fprintf(errout, "%v\n", err)
 				os.Exit(1)
 			}
@@ -324,29 +324,51 @@ func NewDefaultKubectlCommandWithArgs(pluginHandler PluginHandler, args []string
 // and performing executable filename lookups to search
 // for valid plugin files, and execute found plugins.
 type PluginHandler interface {
-	// Lookup receives a potential filename and returns
-	// a full or relative path to an executable, if one
-	// exists at the given filename, or an error.
-	Lookup(filename string) (string, error)
+	// exists at the given filename, or a boolean false.
+	// Lookup will iterate over a list of given prefixes
+	// in order to recognize valid plugin filenames.
+	// The first filepath to match a prefix is returned.
+	Lookup(filename string) (string, bool)
 	// Execute receives an executable's filepath, a slice
 	// of arguments, and a slice of environment variables
 	// to relay to the executable.
 	Execute(executablePath string, cmdArgs, environment []string) error
 }
 
-type defaultPluginHandler struct{}
+// DefaultPluginHandler implements PluginHandler
+type DefaultPluginHandler struct {
+	ValidPrefixes []string
+}
+
+// NewDefaultPluginHandler instantiates the DefaultPluginHandler with a list of
+// given filename prefixes used to identify valid plugin filenames.
+func NewDefaultPluginHandler(validPrefixes []string) *DefaultPluginHandler {
+	return &DefaultPluginHandler{
+		ValidPrefixes: validPrefixes,
+	}
+}
 
 // Lookup implements PluginHandler
-func (h *defaultPluginHandler) Lookup(filename string) (string, error) {
-	return exec.LookPath(filename)
+func (h *DefaultPluginHandler) Lookup(filename string) (string, bool) {
+	for _, prefix := range h.ValidPrefixes {
+		path, err := exec.LookPath(fmt.Sprintf("%s-%s", prefix, filename))
+		if err != nil || len(path) == 0 {
+			continue
+		}
+		return path, true
+	}
+
+	return "", false
 }
 
 // Execute implements PluginHandler
-func (h *defaultPluginHandler) Execute(executablePath string, cmdArgs, environment []string) error {
+func (h *DefaultPluginHandler) Execute(executablePath string, cmdArgs, environment []string) error {
 	return syscall.Exec(executablePath, cmdArgs, environment)
 }
 
-func handleEndpointExtensions(pluginHandler PluginHandler, cmdArgs []string) error {
+// HandlePluginCommand receives a pluginHandler and command-line arguments and attempts to find
+// a plugin executable on the PATH that satisfies the given arguments.
+func HandlePluginCommand(pluginHandler PluginHandler, cmdArgs []string) error {
 	remainingArgs := []string{} // all "non-flag" arguments
 
 	for idx := range cmdArgs {
@@ -360,8 +382,8 @@ func handleEndpointExtensions(pluginHandler PluginHandler, cmdArgs []string) err
 
 	// attempt to find binary, starting at longest possible name with given cmdArgs
 	for len(remainingArgs) > 0 {
-		path, err := pluginHandler.Lookup(fmt.Sprintf("kubectl-%s", strings.Join(remainingArgs, "-")))
-		if err != nil || len(path) == 0 {
+		path, found := pluginHandler.Lookup(strings.Join(remainingArgs, "-"))
+		if !found {
 			remainingArgs = remainingArgs[:len(remainingArgs)-1]
 			continue
 		}

pkg/kubectl/cmd/cmd_test.go

@@ -175,32 +175,35 @@ type testPluginHandler struct {
 	err error
 }
 
-func (h *testPluginHandler) Lookup(filename string) (string, error) {
+func (h *testPluginHandler) Lookup(filename string) (string, bool) {
+	// append supported plugin prefix to the filename
+	filename = fmt.Sprintf("%s-%s", "kubectl", filename)
+
 	dir, err := os.Stat(h.pluginsDirectory)
 	if err != nil {
 		h.err = err
-		return "", err
+		return "", false
 	}
 
 	if !dir.IsDir() {
 		h.err = fmt.Errorf("expected %q to be a directory", h.pluginsDirectory)
-		return "", h.err
+		return "", false
 	}
 
 	plugins, err := ioutil.ReadDir(h.pluginsDirectory)
 	if err != nil {
 		h.err = err
-		return "", err
+		return "", false
 	}
 
 	for _, p := range plugins {
 		if p.Name() == filename {
-			return fmt.Sprintf("%s/%s", h.pluginsDirectory, p.Name()), nil
+			return fmt.Sprintf("%s/%s", h.pluginsDirectory, p.Name()), true
 		}
 	}
 
 	h.err = fmt.Errorf("unable to find a plugin executable %q", filename)
-	return "", h.err
+	return "", false
 }
 
 func (h *testPluginHandler) Execute(executablePath string, cmdArgs, env []string) error {

pkg/kubectl/cmd/plugin/plugin.go

@@ -49,6 +49,8 @@ var (
 		- anywhere on the user's PATH
 		- begin with "kubectl-"
 `)
+
+	ValidPluginFilenamePrefixes = []string{"kubectl"}
 )
 
 func NewCmdPlugin(f cmdutil.Factory, streams genericclioptions.IOStreams) *cobra.Command {
@@ -127,12 +129,12 @@ func (o *PluginListOptions) Run() error {
 			if f.IsDir() {
 				continue
 			}
-			if !strings.HasPrefix(f.Name(), "kubectl-") {
+			if !hasValidPrefix(f.Name(), ValidPluginFilenamePrefixes) {
 				continue
 			}
 
 			if isFirstFile {
-				fmt.Fprintf(o.ErrOut, "The following kubectl-compatible plugins are available:\n\n")
+				fmt.Fprintf(o.ErrOut, "The following compatible plugins are available:\n\n")
 				pluginsFound = true
 				isFirstFile = false
 			}
@@ -262,3 +264,13 @@ func uniquePathsList(paths []string) []string {
 	}
 	return newPaths
 }
+
+func hasValidPrefix(filepath string, validPrefixes []string) bool {
+	for _, prefix := range validPrefixes {
+		if !strings.HasPrefix(filepath, prefix+"-") {
+			continue
+		}
+		return true
+	}
+	return false
+}