[Feature] Basic Plugin System - SubGoal: callables

cmd/root.go

@@ -22,6 +22,7 @@ THE SOFTWARE.
 package cmd
 
 import (
+	"context"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -34,9 +35,9 @@ import (
 	"github.com/rancher/k3d/v3/cmd/image"
 	"github.com/rancher/k3d/v3/cmd/kubeconfig"
 	"github.com/rancher/k3d/v3/cmd/node"
+	cliutil "github.com/rancher/k3d/v3/cmd/util"
 	"github.com/rancher/k3d/v3/pkg/runtimes"
 	"github.com/rancher/k3d/v3/version"
-
 	log "github.com/sirupsen/logrus"
 	"github.com/sirupsen/logrus/hooks/writer"
 )
@@ -73,6 +74,19 @@ All Nodes of a k3d cluster are part of the same docker network.`,
 // Execute adds all child commands to the root command and sets flags appropriately.
 // This is called by main.main(). It only needs to happen once to the rootCmd.
 func Execute() {
+	if len(os.Args) > 1 {
+		parts := os.Args[1:]
+		// Check if it's a built-in command, else try to execute it as a plugin
+		if _, _, err := rootCmd.Find(parts); err != nil {
+			pluginFound, err := cliutil.HandlePlugin(context.Background(), parts)
+			if err != nil {
+				log.Errorf("Failed to execute plugin '%+v'", parts)
+				log.Fatalln(err)
+			} else if pluginFound {
+				os.Exit(0)
+			}
+		}
+	}
 	if err := rootCmd.Execute(); err != nil {
 		log.Fatalln(err)
 	}

cmd/util/plugins.go

@@ -0,0 +1,84 @@
+/*
+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 (
+	"context"
+	"fmt"
+	"os"
+	"os/exec"
+	"strings"
+
+	k3d "github.com/rancher/k3d/v3/pkg/types"
+)
+
+// HandlePlugin takes care of finding and executing a plugin based on the longest prefix
+func HandlePlugin(ctx context.Context, args []string) (bool, 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 false, nil
+	}
+
+	return true, ExecPlugin(ctx, 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(ctx context.Context, path string, args []string, env []string) error {
+	cmd := exec.CommandContext(ctx, path, args...)
+	cmd.Env = env
+	cmd.Stderr = os.Stderr
+	cmd.Stdout = os.Stdout
+	cmd.Stdin = os.Stdin
+	return cmd.Run()
+}