init plugin system

cmd/root.go

@@ -60,6 +60,17 @@ k3d is a wrapper CLI that helps you to easily create k3s clusters inside docker.
 Nodes of a k3d cluster are docker containers running a k3s image.
 All Nodes of a k3d cluster are part of the same docker network.`,
 	Run: func(cmd *cobra.Command, args []string) {
+		if len(args) > 1 {
+			parts := args[1:]
+
+			// Check if it's a built-in command, else try to execute it as a plugin
+			if _, _, err := cmd.Find(parts); err != nil {
+				if err := util.HandlePlugin(parts); err != nil {
+					log.Errorf("Failed to execute plugin '%+v'", parts)
+					log.Fatalln(err)
+				}
+			}
+		}
 		if flags.version {
 			printVersion()
 		} else {

cmd/util/plugins.go

@@ -0,0 +1,76 @@
+/*
+Copyright © 2020 The k3d Author(s)
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
+*/
+package util
+
+import (
+	"fmt"
+	"os"
+	"os/exec"
+	"strings"
+)
+
+func HandlePlugin(args []string) error {
+	argsPrefix := []string{}
+
+	for _, arg := range args {
+		if strings.HasPrefix(arg, "-") {
+			continue // drop flags
+		}
+		argsPrefix = append(argsPrefix, strings.ReplaceAll(arg, "-", "_")) // plugin executables assumed to have underscores
+	}
+
+	execPath := ""
+
+	for len(argsPrefix) > 0 {
+		path, found := FindPlugin(strings.Join(argsPrefix, "-"))
+
+		if !found {
+			argsPrefix = argsPrefix[:len(argsPrefix)-1] // drop last element
+			continue
+		}
+
+		execPath = path
+		break
+	}
+
+	if execPath == "" {
+		return nil
+	}
+
+	return ExecPlugin(execPath, args[len(argsPrefix):], os.Environ())
+
+}
+
+// FindPlugin tries to find the plugin executable on the filesystem
+func FindPlugin(name string) (string, bool) {
+	path, err := exec.LookPath(fmt.Sprintf("%s-%s", k3d.DefaultObjectNamePrefix, name))
+	if err == nil && len(path) > 0 {
+		return path, true
+	}
+	return "", false
+}
+
+// ExecPlugin executes a found plugin
+func ExecPlugin(path string, args []string, env []string) error {
+
+	return nil
+}