Refactor plugin & version subcommands (#1359)

pkg/plugin/plugin.go

@@ -0,0 +1,179 @@
+/*
+Copyright 2016 The Fission 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 provides support for creating extensible CLIs
+package plugin
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"errors"
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"path"
+	"strings"
+	"time"
+)
+
+const (
+	cmdTimeout      = 5 * time.Second
+	cmdMetadataArgs = "--plugin"
+)
+
+var (
+	ErrPluginNotFound = errors.New("plugin not found")
+	ErrPluginInvalid  = errors.New("invalid plugin")
+
+	Prefix = "fission-"
+)
+
+// Metadata contains the metadata of a plugin.
+// The only metadata that is guaranteed to be non-empty is the path and Name. All other fields are considered optional.
+type Metadata struct {
+	Name    string   `json:"name,omitempty"`
+	Version string   `json:"version,omitempty"`
+	Aliases []string `json:"aliases,omitempty"`
+	Usage   string   `json:"usage,omitempty"`
+	Path    string   `json:"path,omitempty"`
+}
+
+func (md *Metadata) AddAlias(alias string) {
+	if alias != md.Name && !md.HasAlias(alias) {
+		md.Aliases = append(md.Aliases, alias)
+	}
+}
+
+func (md *Metadata) HasAlias(needle string) bool {
+	for _, alias := range md.Aliases {
+		if alias == needle {
+			return true
+		}
+	}
+	return false
+}
+
+// Find searches the machine for the given plugin, returning the metadata of the plugin.
+// The only metadata that is guaranteed to be non-empty is the path and Name. All other fields are considered optional.
+// If found it returns the plugin, otherwise it returns ErrPluginNotFound if the plugin was not found.
+func Find(pluginName string) (*Metadata, error) {
+	// Search PATH for plugin as command-name
+	// To check if plugin is actually there still.
+	pluginPath, err := findPluginOnPath(pluginName)
+	if err != nil {
+		// Fallback: Search for alias in each command
+		mds := FindAll()
+		for _, md := range mds {
+			if md.HasAlias(pluginName) {
+				return md, nil
+			}
+		}
+		return nil, ErrPluginNotFound
+	}
+
+	md, err := fetchPluginMetadata(pluginPath)
+	if err != nil {
+		return nil, err
+	}
+	return md, nil
+}
+
+// Exec executes the plugin using the provided args.
+// All input and output is redirected to stdin, stdout, and stderr.
+func Exec(md *Metadata, args []string) error {
+	cmd := exec.Command(md.Path, args...)
+	cmd.Stdin = os.Stdin
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+	return cmd.Run()
+}
+
+// FindAll searches the machine for all plugins currently present.
+func FindAll() map[string]*Metadata {
+	plugins := map[string]*Metadata{}
+
+	dirs := strings.Split(os.Getenv("PATH"), ":")
+	for _, dir := range dirs {
+		fs, err := ioutil.ReadDir(dir)
+		if err != nil {
+			continue
+		}
+		for _, f := range fs {
+			if !strings.HasPrefix(f.Name(), Prefix) {
+				continue
+			}
+			fp := path.Join(dir, f.Name())
+			md, err := fetchPluginMetadata(fp)
+			if err != nil {
+				continue
+			}
+			if existing, ok := plugins[md.Name]; ok {
+				for _, alias := range existing.Aliases {
+					md.AddAlias(alias)
+				}
+			}
+			plugins[md.Name] = md
+		}
+	}
+	return plugins
+}
+
+func findPluginOnPath(pluginName string) (path string, err error) {
+	binaryName := Prefix + pluginName
+	path, err = exec.LookPath(binaryName)
+
+	if err != nil || len(path) == 0 {
+		return "", ErrPluginNotFound
+	}
+	return path, nil
+}
+
+// fetchPluginMetadata attempts to fetch the plugin metadata given the plugin path.
+func fetchPluginMetadata(pluginPath string) (*Metadata, error) {
+	d, err := os.Stat(pluginPath)
+	if err != nil {
+		return nil, ErrPluginNotFound
+	}
+	if m := d.Mode(); m.IsDir() || m&0111 == 0 {
+		return nil, ErrPluginInvalid
+	}
+
+	// Fetch the metadata from the plugin itself.
+	buf := bytes.NewBuffer(nil)
+	ctx, cancel := context.WithTimeout(context.Background(), cmdTimeout)
+	defer cancel()
+
+	cmd := exec.CommandContext(ctx, pluginPath, cmdMetadataArgs) // Note: issue can occur with signal propagation
+	cmd.Stdout = buf
+	err = cmd.Run()
+	if err != nil {
+		return nil, err
+	}
+
+	// Parse metadata if possible
+	pluginName := strings.TrimPrefix(path.Base(pluginPath), Prefix)
+	md := &Metadata{}
+	err = json.Unmarshal(buf.Bytes(), md)
+
+	// If metadata could not be retrieved, or if no name was provided, use the filename of the binary
+	if err != nil || len(md.Name) == 0 {
+		md.Name = pluginName
+	}
+	md.Path = pluginPath
+	md.AddAlias(pluginName)
+	return md, nil
+}