plugin_manager.go

package command

import (
	"encoding/json"
	"fmt"
	"io"
	"log"
	"os"
	"os/exec"
	"runtime"
	"sync"

	"github.com/hashicorp/go-multierror"
	"github.com/hashicorp/otto/app"
	"github.com/hashicorp/otto/helper/semaphore"
	"github.com/hashicorp/otto/otto"
	"github.com/hashicorp/otto/plugin"
	"github.com/kardianos/osext"
)

// PluginGlob is the glob pattern used to find plugins.
const PluginGlob = "otto-plugin-*"

// PluginManager is responsible for discovering and starting plugins.
//
// Plugin cleanup is done out in the main package: we just defer
// plugin.CleanupClients in main itself.
type PluginManager struct {
	// PluginDirs are the directories where plugins can be found.
	// Any plugins with the same types found later (higher index) will
	// override earlier (lower index) directories.
	PluginDirs []string

	// PluginMap is the map of availabile built-in plugins
	PluginMap plugin.ServeMuxMap

	plugins []*Plugin
}

// Plugin is a single plugin that has been loaded.
type Plugin struct {
	// Path and Args are the method used to invocate this plugin.
	// These are the only two values that need to be set manually. Once
	// these are set, call Load to load the plugin.
	Path string   `json:"path,omitempty"`
	Args []string `json:"args"`

	// Builtin will be set to true by the PluginManager if this plugin
	// represents a built-in plugin. If it does, then Path above has
	// no affect, we always use the current executable.
	Builtin bool `json:"builtin"`

	// The fields below are loaded as part of the Load() call and should
	// not be set manually, but can be accessed after Load.
	App     app.Factory `json:"-"`
	AppMeta *app.Meta   `json:"-"`

	used bool
}

// Load loads the plugin specified by the Path and instantiates the
// other fields on this structure.
func (p *Plugin) Load() error {
	// If it is builtin, then we always use our own path
	path := p.Path
	if p.Builtin {
		path = pluginExePath
	}

	// Create the plugin client to communicate with the process
	pluginClient := plugin.NewClient(&plugin.ClientConfig{
		Cmd:        exec.Command(path, p.Args...),
		Managed:    true,
		SyncStdout: os.Stdout,
		SyncStderr: os.Stderr,
	})

	// Request the client
	client, err := pluginClient.Client()
	if err != nil {
		return err
	}

	// Get the app implementation
	appImpl, err := client.App()
	if err != nil {
		return err
	}
	if c, ok := appImpl.(io.Closer); ok {
		defer c.Close()
	}

	p.AppMeta, err = appImpl.Meta()
	if err != nil {
		return err
	}

	// Create a custom factory that when called marks the plugin as used
	p.used = false
	p.App = func() (app.App, error) {
		p.used = true
		return client.App()
	}

	return nil
}

// Used tracks whether or not this plugin was used or not. You can call
// this after compilation on each plugin to determine what plugin
// was used.
func (p *Plugin) Used() bool {
	return p.used
}

func (p *Plugin) String() string {
	path := p.Path
	if p.Builtin {
		path = "<builtin>"
	}

	return fmt.Sprintf("%s %v", path, p.Args)
}

// ConfigureCore configures the Otto core configuration with the loaded
// plugin data.
func (m *PluginManager) ConfigureCore(core *otto.CoreConfig) error {
	if core.Apps == nil {
		core.Apps = make(map[app.Tuple]app.Factory)
	}

	for _, p := range m.Plugins() {
		for _, tuple := range p.AppMeta.Tuples {
			core.Apps[tuple] = p.App
		}
	}

	return nil
}

// Plugins returns the loaded plugins.
func (m *PluginManager) Plugins() []*Plugin {
	return m.plugins
}

// Discover will find all the available plugin binaries. Each time this
// is called it will override any previously discovered plugins.
func (m *PluginManager) Discover() error {
	result := make([]*Plugin, 0, 20)

	if !testingMode {
		// First we add all the builtin plugins which we get by executing ourself
		for k, _ := range m.PluginMap {
			result = append(result, &Plugin{
				Args:    []string{"plugin-builtin", k},
				Builtin: true,
			})
		}
	}

	for _, dir := range m.PluginDirs {
		log.Printf("[DEBUG] Looking for plugins in: %s", dir)
		paths, err := plugin.Discover(PluginGlob, dir)
		if err != nil {
			return fmt.Errorf(
				"Error discovering plugins in %s: %s", dir, err)
		}

		for _, path := range paths {
			result = append(result, &Plugin{
				Path: path,
			})
		}
	}

	// Reverse the list of plugins. We do this because we want custom
	// plugins to take priority over built-in plugins, and the PluginDirs
	// ordering also defines this priority.
	for left, right := 0, len(result)-1; left < right; left, right = left+1, right-1 {
		result[left], result[right] = result[right], result[left]
	}

	// Log it
	for _, r := range result {
		log.Printf("[DEBUG] Detected plugin: %s", r)
	}

	// Save our result
	m.plugins = result

	return nil
}

// StoreUsed will persist the used plugins into a file. LoadUsed can
// then be called to load the plugins that were used only, making plugin
// loading much more efficient.
func (m *PluginManager) StoreUsed(path string) error {
	// Get the used plugins
	plugins := make([]*Plugin, 0, 2)
	for _, p := range m.Plugins() {
		if p.Used() {
			plugins = append(plugins, p)
		}
	}

	// Write the used plugins to the given path as JSON
	f, err := os.Create(path)
	if err != nil {
		return err
	}
	defer f.Close()

	enc := json.NewEncoder(f)
	return enc.Encode(&usedPluginWrapper{
		Version: usedPluginVersion,
		Plugins: plugins,
	})
}

// LoadUsed will load the plugins in the given used file that was saved
// with StoreUsed.
func (m *PluginManager) LoadUsed(path string) error {
	f, err := os.Open(path)
	if err != nil {
		return err
	}

	var wrapper usedPluginWrapper
	dec := json.NewDecoder(f)
	err = dec.Decode(&wrapper)
	f.Close()
	if err != nil {
		return err
	}

	if wrapper.Version > usedPluginVersion {
		return fmt.Errorf(
			"Couldn't load used plugins because the format of the stored\n" +
				"metadata is newer than this version of Otto knows how to read.\n\n" +
				"This is usually caused by a newer version of Otto compiling an\n" +
				"environment. Please use a later version of Otto to read this.")
	}

	m.plugins = wrapper.Plugins
	return m.LoadAll()
}

// LoadAll will launch every plugin and add it to the CoreConfig given.
func (m *PluginManager) LoadAll() error {
	// If we've never loaded plugin paths, then let's discover those first
	if m.Plugins() == nil {
		if err := m.Discover(); err != nil {
			return err
		}
	}

	// Go through each plugin path and load single
	var merr error
	var merrLock sync.Mutex
	var wg sync.WaitGroup
	sema := semaphore.New(runtime.NumCPU())
	for _, plugin := range m.Plugins() {
		wg.Add(1)
		go func(plugin *Plugin) {
			defer wg.Done()

			sema.Acquire()
			defer sema.Release()

			if err := plugin.Load(); err != nil {
				merrLock.Lock()
				defer merrLock.Unlock()
				merr = multierror.Append(merr, fmt.Errorf(
					"Error loading plugin %s: %s",
					plugin.Path, err))
			}
		}(plugin)
	}

	// Wait for all the plugins to load
	wg.Wait()

	return merr
}

// usedPluginVersion is the current version of the used plugin format
// that we understand. We can increment and handle older versions as we go.
const usedPluginVersion int = 1

type usedPluginWrapper struct {
	Version int       `json:"version"`
	Plugins []*Plugin `json:"plugins"`
}

// pluginExePath is our own path. We cache this so we only have to calculate
// it once.
var pluginExePath string

func init() {
	var err error
	pluginExePath, err = osext.Executable()
	if err != nil {
		panic(err)
	}
}