Add plugin slash command support (#7941)

* add plugin slash command support

* remove unused string

* rebase

19 files changed, 560 insertions, 38 deletions

diff --git a/api4/plugin_test.go b/api4/plugin_test.go
index 82e11f775..e385b5c8c 100644
--- a/api4/plugin_test.go
+++ b/api4/plugin_test.go
@@ -46,7 +46,7 @@ func TestPlugin(t *testing.T) {
 		*cfg.PluginSettings.EnableUploads = true
 	})
 
-	th.App.InitPlugins(pluginDir, webappDir)
+	th.App.InitPlugins(pluginDir, webappDir, nil)
 	defer func() {
 		th.App.ShutDownPlugins()
 		th.App.PluginEnv = nil
diff --git a/app/app.go b/app/app.go
index fd313c9c9..959c99306 100644
--- a/app/app.go
+++ b/app/app.go
@@ -9,6 +9,7 @@ import (
 	"net/http"
 	"runtime/debug"
 	"strings"
+	"sync"
 	"sync/atomic"
 
 	l4g "github.com/alecthomas/log4go"
@@ -60,6 +61,9 @@ type App struct {
 	sessionCache        *utils.Cache
 	roles               map[string]*model.Role
 	configListenerId    string
+
+	pluginCommands     []*PluginCommand
+	pluginCommandsLock sync.RWMutex
 }
 
 var appCount = 0
diff --git a/app/apptestlib.go b/app/apptestlib.go
index 63a064d7f..618ad809a 100644
--- a/app/apptestlib.go
+++ b/app/apptestlib.go
@@ -4,15 +4,21 @@
 package app
 
 import (
+	"encoding/json"
+	"io/ioutil"
+	"os"
+	"path/filepath"
 	"time"
 
+	l4g "github.com/alecthomas/log4go"
+
 	"github.com/mattermost/mattermost-server/model"
+	"github.com/mattermost/mattermost-server/plugin"
+	"github.com/mattermost/mattermost-server/plugin/pluginenv"
 	"github.com/mattermost/mattermost-server/store"
 	"github.com/mattermost/mattermost-server/store/sqlstore"
 	"github.com/mattermost/mattermost-server/store/storetest"
 	"github.com/mattermost/mattermost-server/utils"
-
-	l4g "github.com/alecthomas/log4go"
 )
 
 type TestHelper struct {
@@ -22,6 +28,9 @@ type TestHelper struct {
 	BasicUser2   *model.User
 	BasicChannel *model.Channel
 	BasicPost    *model.Post
+
+	tempWorkspace string
+	pluginHooks   map[string]plugin.Hooks
 }
 
 type persistentTestStore struct {
@@ -54,7 +63,8 @@ func setupTestHelper(enterprise bool) *TestHelper {
 	}
 
 	th := &TestHelper{
-		App: New(options...),
+		App:         New(options...),
+		pluginHooks: make(map[string]plugin.Hooks),
 	}
 
 	th.App.UpdateConfig(func(cfg *model.Config) { *cfg.TeamSettings.MaxUsersPerTeam = 50 })
@@ -223,4 +233,61 @@ func (me *TestHelper) TearDown() {
 		StopTestStore()
 		panic(err)
 	}
+	if me.tempWorkspace != "" {
+		os.RemoveAll(me.tempWorkspace)
+	}
+}
+
+type mockPluginSupervisor struct {
+	hooks plugin.Hooks
+}
+
+func (s *mockPluginSupervisor) Start(api plugin.API) error {
+	return s.hooks.OnActivate(api)
+}
+
+func (s *mockPluginSupervisor) Stop() error {
+	return nil
+}
+
+func (s *mockPluginSupervisor) Hooks() plugin.Hooks {
+	return s.hooks
+}
+
+func (me *TestHelper) InstallPlugin(manifest *model.Manifest, hooks plugin.Hooks) {
+	if me.tempWorkspace == "" {
+		dir, err := ioutil.TempDir("", "apptest")
+		if err != nil {
+			panic(err)
+		}
+		me.tempWorkspace = dir
+	}
+
+	pluginDir := filepath.Join(me.tempWorkspace, "plugins")
+	webappDir := filepath.Join(me.tempWorkspace, "webapp")
+	me.App.InitPlugins(pluginDir, webappDir, func(bundle *model.BundleInfo) (plugin.Supervisor, error) {
+		if hooks, ok := me.pluginHooks[bundle.Manifest.Id]; ok {
+			return &mockPluginSupervisor{hooks}, nil
+		}
+		return pluginenv.DefaultSupervisorProvider(bundle)
+	})
+
+	me.pluginHooks[manifest.Id] = hooks
+
+	manifestCopy := *manifest
+	if manifestCopy.Backend == nil {
+		manifestCopy.Backend = &model.ManifestBackend{}
+	}
+	manifestBytes, err := json.Marshal(&manifestCopy)
+	if err != nil {
+		panic(err)
+	}
+
+	if err := os.MkdirAll(filepath.Join(pluginDir, manifest.Id), 0700); err != nil {
+		panic(err)
+	}
+
+	if err := ioutil.WriteFile(filepath.Join(pluginDir, manifest.Id, "plugin.json"), manifestBytes, 0600); err != nil {
+		panic(err)
+	}
 }
diff --git a/app/command.go b/app/command.go
index dc65de6e2..4c26eae71 100644
--- a/app/command.go
+++ b/app/command.go
@@ -75,6 +75,13 @@ func (a *App) ListAutocompleteCommands(teamId string, T goi18n.TranslateFunc) ([
 		}
 	}
 
+	for _, cmd := range a.PluginCommandsForTeam(teamId) {
+		if cmd.AutoComplete && !seen[cmd.Trigger] {
+			seen[cmd.Trigger] = true
+			commands = append(commands, cmd)
+		}
+	}
+
 	if *a.Config().ServiceSettings.EnableCommands {
 		if result := <-a.Srv.Store.Command().GetByTeam(teamId); result.Err != nil {
 			return nil, result.Err
@@ -111,7 +118,7 @@ func (a *App) ListAllCommands(teamId string, T goi18n.TranslateFunc) ([]*model.C
 	for _, value := range commandProviders {
 		if cmd := value.GetCommand(a, T); cmd != nil {
 			cpy := *cmd
-			if cpy.AutoComplete && !seen[cpy.Id] {
+			if cpy.AutoComplete && !seen[cpy.Trigger] {
 				cpy.Sanitize()
 				seen[cpy.Trigger] = true
 				commands = append(commands, &cpy)
@@ -119,13 +126,20 @@ func (a *App) ListAllCommands(teamId string, T goi18n.TranslateFunc) ([]*model.C
 		}
 	}
 
+	for _, cmd := range a.PluginCommandsForTeam(teamId) {
+		if !seen[cmd.Trigger] {
+			seen[cmd.Trigger] = true
+			commands = append(commands, cmd)
+		}
+	}
+
 	if *a.Config().ServiceSettings.EnableCommands {
 		if result := <-a.Srv.Store.Command().GetByTeam(teamId); result.Err != nil {
 			return nil, result.Err
 		} else {
 			teamCmds := result.Data.([]*model.Command)
 			for _, cmd := range teamCmds {
-				if !seen[cmd.Id] {
+				if !seen[cmd.Trigger] {
 					cmd.Sanitize()
 					seen[cmd.Trigger] = true
 					commands = append(commands, cmd)
@@ -151,6 +165,12 @@ func (a *App) ExecuteCommand(args *model.CommandArgs) (*model.CommandResponse, *
 		}
 	}
 
+	if cmd, response, err := a.ExecutePluginCommand(args); err != nil {
+		return nil, err
+	} else if cmd != nil {
+		return a.HandleCommandResponse(cmd, args, response, true)
+	}
+
 	if !*a.Config().ServiceSettings.EnableCommands {
 		return nil, model.NewAppError("ExecuteCommand", "api.command.disabled.app_error", nil, "", http.StatusNotImplemented)
 	}
diff --git a/app/plugin.go b/app/plugin.go
index f91a2e414..661f6ed5d 100644
--- a/app/plugin.go
+++ b/app/plugin.go
@@ -8,6 +8,7 @@ import (
 	"context"
 	"crypto/sha256"
 	"encoding/base64"
+	"fmt"
 	"io"
 	"io/ioutil"
 	"net/http"
@@ -101,20 +102,28 @@ func (a *App) ActivatePlugins() {
 
 			l4g.Info("Activated %v plugin", id)
 		} else if !pluginState.Enable && active {
-			if err := a.PluginEnv.DeactivatePlugin(id); err != nil {
+			if err := a.deactivatePlugin(plugin.Manifest); err != nil {
 				l4g.Error(err.Error())
-				continue
 			}
+		}
+	}
+}
 
-			if plugin.Manifest.HasClient() {
-				message := model.NewWebSocketEvent(model.WEBSOCKET_EVENT_PLUGIN_DEACTIVATED, "", "", "", nil)
-				message.Add("manifest", plugin.Manifest.ClientManifest())
-				a.Publish(message)
-			}
+func (a *App) deactivatePlugin(manifest *model.Manifest) *model.AppError {
+	if err := a.PluginEnv.DeactivatePlugin(manifest.Id); err != nil {
+		return model.NewAppError("removePlugin", "app.plugin.deactivate.app_error", nil, err.Error(), http.StatusBadRequest)
+	}
 
-			l4g.Info("Deactivated %v plugin", id)
-		}
+	a.UnregisterPluginCommands(manifest.Id)
+
+	if manifest.HasClient() {
+		message := model.NewWebSocketEvent(model.WEBSOCKET_EVENT_PLUGIN_DEACTIVATED, "", "", "", nil)
+		message.Add("manifest", manifest.ClientManifest())
+		a.Publish(message)
 	}
+
+	l4g.Info("Deactivated %v plugin", manifest.Id)
+	return nil
 }
 
 // InstallPlugin unpacks and installs a plugin but does not activate it.
@@ -253,15 +262,9 @@ func (a *App) removePlugin(id string, allowPrepackaged bool) *model.AppError {
 	}
 
 	if a.PluginEnv.IsPluginActive(id) {
-		err := a.PluginEnv.DeactivatePlugin(id)
+		err := a.deactivatePlugin(manifest)
 		if err != nil {
-			return model.NewAppError("removePlugin", "app.plugin.deactivate.app_error", nil, err.Error(), http.StatusBadRequest)
-		}
-
-		if manifest.HasClient() {
-			message := model.NewWebSocketEvent(model.WEBSOCKET_EVENT_PLUGIN_DEACTIVATED, "", "", "", nil)
-			message.Add("manifest", manifest.ClientManifest())
-			a.Publish(message)
+			return err
 		}
 	}
 
@@ -341,7 +344,7 @@ func (a *App) DisablePlugin(id string) *model.AppError {
 	return nil
 }
 
-func (a *App) InitPlugins(pluginPath, webappPath string) {
+func (a *App) InitPlugins(pluginPath, webappPath string, supervisorOverride pluginenv.SupervisorProviderFunc) {
 	if !*a.Config().PluginSettings.Enable {
 		return
 	}
@@ -362,7 +365,7 @@ func (a *App) InitPlugins(pluginPath, webappPath string) {
 		return
 	}
 
-	if env, err := pluginenv.New(
+	options := []pluginenv.Option{
 		pluginenv.SearchPath(pluginPath),
 		pluginenv.WebappPath(webappPath),
 		pluginenv.APIProvider(func(m *model.Manifest) (plugin.API, error) {
@@ -375,7 +378,13 @@ func (a *App) InitPlugins(pluginPath, webappPath string) {
 				},
 			}, nil
 		}),
-	); err != nil {
+	}
+
+	if supervisorOverride != nil {
+		options = append(options, pluginenv.SupervisorProvider(supervisorOverride))
+	}
+
+	if env, err := pluginenv.New(options...); err != nil {
 		l4g.Error("failed to start up plugins: " + err.Error())
 		return
 	} else {
@@ -533,3 +542,101 @@ func (a *App) DeletePluginKey(pluginId string, key string) *model.AppError {
 
 	return result.Err
 }
+
+type PluginCommand struct {
+	Command  *model.Command
+	PluginId string
+}
+
+func (a *App) RegisterPluginCommand(pluginId string, command *model.Command) error {
+	if command.Trigger == "" {
+		return fmt.Errorf("invalid command")
+	}
+
+	command = &model.Command{
+		Trigger:          strings.ToLower(command.Trigger),
+		TeamId:           command.TeamId,
+		AutoComplete:     command.AutoComplete,
+		AutoCompleteDesc: command.AutoCompleteDesc,
+		DisplayName:      command.DisplayName,
+	}
+
+	a.pluginCommandsLock.Lock()
+	defer a.pluginCommandsLock.Unlock()
+
+	for _, pc := range a.pluginCommands {
+		if pc.Command.Trigger == command.Trigger && pc.Command.TeamId == command.TeamId {
+			if pc.PluginId == pluginId {
+				pc.Command = command
+				return nil
+			}
+		}
+	}
+
+	a.pluginCommands = append(a.pluginCommands, &PluginCommand{
+		Command:  command,
+		PluginId: pluginId,
+	})
+	return nil
+}
+
+func (a *App) UnregisterPluginCommand(pluginId, teamId, trigger string) {
+	trigger = strings.ToLower(trigger)
+
+	a.pluginCommandsLock.Lock()
+	defer a.pluginCommandsLock.Unlock()
+
+	var remaining []*PluginCommand
+	for _, pc := range a.pluginCommands {
+		if pc.Command.TeamId != teamId || pc.Command.Trigger != trigger {
+			remaining = append(remaining, pc)
+		}
+	}
+	a.pluginCommands = remaining
+}
+
+func (a *App) UnregisterPluginCommands(pluginId string) {
+	a.pluginCommandsLock.Lock()
+	defer a.pluginCommandsLock.Unlock()
+
+	var remaining []*PluginCommand
+	for _, pc := range a.pluginCommands {
+		if pc.PluginId != pluginId {
+			remaining = append(remaining, pc)
+		}
+	}
+	a.pluginCommands = remaining
+}
+
+func (a *App) PluginCommandsForTeam(teamId string) []*model.Command {
+	a.pluginCommandsLock.RLock()
+	defer a.pluginCommandsLock.RUnlock()
+
+	var commands []*model.Command
+	for _, pc := range a.pluginCommands {
+		if pc.Command.TeamId == "" || pc.Command.TeamId == teamId {
+			commands = append(commands, pc.Command)
+		}
+	}
+	return commands
+}
+
+func (a *App) ExecutePluginCommand(args *model.CommandArgs) (*model.Command, *model.CommandResponse, *model.AppError) {
+	parts := strings.Split(args.Command, " ")
+	trigger := parts[0][1:]
+	trigger = strings.ToLower(trigger)
+
+	a.pluginCommandsLock.RLock()
+	defer a.pluginCommandsLock.RUnlock()
+
+	for _, pc := range a.pluginCommands {
+		if (pc.Command.TeamId == "" || pc.Command.TeamId == args.TeamId) && pc.Command.Trigger == trigger {
+			response, appErr, err := a.PluginEnv.HooksForPlugin(pc.PluginId).ExecuteCommand(args)
+			if err != nil {
+				return pc.Command, nil, model.NewAppError("ExecutePluginCommand", "model.plugin_command.error.app_error", nil, "err="+err.Error(), http.StatusInternalServerError)
+			}
+			return pc.Command, response, appErr
+		}
+	}
+	return nil, nil, nil
+}
diff --git a/app/plugin_api.go b/app/plugin_api.go
index 9965f770a..21b828368 100644
--- a/app/plugin_api.go
+++ b/app/plugin_api.go
@@ -34,6 +34,15 @@ func (api *PluginAPI) LoadPluginConfiguration(dest interface{}) error {
 	}
 }
 
+func (api *PluginAPI) RegisterCommand(command *model.Command) error {
+	return api.app.RegisterPluginCommand(api.id, command)
+}
+
+func (api *PluginAPI) UnregisterCommand(teamId, trigger string) error {
+	api.app.UnregisterPluginCommand(api.id, teamId, trigger)
+	return nil
+}
+
 func (api *PluginAPI) CreateTeam(team *model.Team) (*model.Team, *model.AppError) {
 	return api.app.CreateTeam(team)
 }
diff --git a/app/plugin_test.go b/app/plugin_test.go
index 5c70cbc4f..4794d2704 100644
--- a/app/plugin_test.go
+++ b/app/plugin_test.go
@@ -13,6 +13,8 @@ import (
 	"github.com/stretchr/testify/require"
 
 	"github.com/mattermost/mattermost-server/model"
+	"github.com/mattermost/mattermost-server/plugin"
+	"github.com/mattermost/mattermost-server/plugin/plugintest"
 )
 
 func TestPluginKeyValueStore(t *testing.T) {
@@ -98,3 +100,98 @@ func TestHandlePluginRequest(t *testing.T) {
 	}
 	router.ServeHTTP(nil, r)
 }
+
+type testPlugin struct {
+	plugintest.Hooks
+}
+
+func (p *testPlugin) OnConfigurationChange() error {
+	return nil
+}
+
+func (p *testPlugin) OnDeactivate() error {
+	return nil
+}
+
+type pluginCommandTestPlugin struct {
+	testPlugin
+
+	TeamId string
+}
+
+func (p *pluginCommandTestPlugin) OnActivate(api plugin.API) error {
+	if err := api.RegisterCommand(&model.Command{
+		Trigger: "foo",
+		TeamId:  p.TeamId,
+	}); err != nil {
+		return err
+	}
+	if err := api.RegisterCommand(&model.Command{
+		Trigger: "foo2",
+		TeamId:  p.TeamId,
+	}); err != nil {
+		return err
+	}
+	return api.UnregisterCommand(p.TeamId, "foo2")
+}
+
+func (p *pluginCommandTestPlugin) ExecuteCommand(args *model.CommandArgs) (*model.CommandResponse, *model.AppError) {
+	if args.Command == "/foo" {
+		return &model.CommandResponse{
+			Text: "bar",
+		}, nil
+	}
+	return nil, model.NewAppError("ExecuteCommand", "this is an error", nil, "", http.StatusBadRequest)
+}
+
+func TestPluginCommands(t *testing.T) {
+	th := Setup().InitBasic()
+	defer th.TearDown()
+
+	th.InstallPlugin(&model.Manifest{
+		Id: "foo",
+	}, &pluginCommandTestPlugin{
+		TeamId: th.BasicTeam.Id,
+	})
+
+	require.Nil(t, th.App.EnablePlugin("foo"))
+
+	resp, err := th.App.ExecuteCommand(&model.CommandArgs{
+		Command:   "/foo2",
+		TeamId:    th.BasicTeam.Id,
+		UserId:    th.BasicUser.Id,
+		ChannelId: th.BasicChannel.Id,
+	})
+	require.NotNil(t, err)
+	assert.Equal(t, http.StatusNotFound, err.StatusCode)
+
+	resp, err = th.App.ExecuteCommand(&model.CommandArgs{
+		Command:   "/foo",
+		TeamId:    th.BasicTeam.Id,
+		UserId:    th.BasicUser.Id,
+		ChannelId: th.BasicChannel.Id,
+	})
+	require.Nil(t, err)
+	assert.Equal(t, "bar", resp.Text)
+
+	resp, err = th.App.ExecuteCommand(&model.CommandArgs{
+		Command:   "/foo baz",
+		TeamId:    th.BasicTeam.Id,
+		UserId:    th.BasicUser.Id,
+		ChannelId: th.BasicChannel.Id,
+	})
+	require.NotNil(t, err)
+	require.Equal(t, "this is an error", err.Message)
+	assert.Nil(t, resp)
+
+	require.Nil(t, th.App.RemovePlugin("foo"))
+
+	resp, err = th.App.ExecuteCommand(&model.CommandArgs{
+		Command:   "/foo",
+		TeamId:    th.BasicTeam.Id,
+		UserId:    th.BasicUser.Id,
+		ChannelId: th.BasicChannel.Id,
+	})
+	require.NotNil(t, err)
+	assert.Equal(t, http.StatusNotFound, err.StatusCode)
+}
diff --git a/cmd/platform/server.go b/cmd/platform/server.go
index 67e2dcc56..4c36f5a46 100644
--- a/cmd/platform/server.go
+++ b/cmd/platform/server.go
@@ -75,10 +75,10 @@ func runServer(configFileLocation string) {
 		a.LoadLicense()
 	}
 
-	a.InitPlugins(*a.Config().PluginSettings.Directory, *a.Config().PluginSettings.ClientDirectory)
+	a.InitPlugins(*a.Config().PluginSettings.Directory, *a.Config().PluginSettings.ClientDirectory, nil)
 	utils.AddConfigListener(func(prevCfg, cfg *model.Config) {
 		if *cfg.PluginSettings.Enable {
-			a.InitPlugins(*cfg.PluginSettings.Directory, *a.Config().PluginSettings.ClientDirectory)
+			a.InitPlugins(*cfg.PluginSettings.Directory, *a.Config().PluginSettings.ClientDirectory, nil)
 		} else {
 			a.ShutDownPlugins()
 		}
diff --git a/i18n/en.json b/i18n/en.json
index f4ddaf217..bf2611a4d 100644
--- a/i18n/en.json
+++ b/i18n/en.json
@@ -4267,6 +4267,10 @@
     "translation": "Current working directory is %v"
   },
   {
+    "id": "model.plugin_command.error.app_error",
+    "translation": "An error occurred while trying to execute this command."
+  },
+  {
     "id": "model.plugin_key_value.is_valid.plugin_id.app_error",
     "translation": "Invalid plugin ID, must be more than {{.Min}} and a of maximum {{.Max}} characters long."
   },
diff --git a/plugin/api.go b/plugin/api.go
index fee55eeff..437188f6e 100644
--- a/plugin/api.go
+++ b/plugin/api.go
@@ -16,6 +16,13 @@ type API interface {
 	// struct that the configuration JSON can be unmarshalled to.
 	LoadPluginConfiguration(dest interface{}) error
 
+	// RegisterCommand registers a custom slash command. When the command is triggered, your plugin
+	// can fulfill it via the ExecuteCommand hook.
+	RegisterCommand(command *model.Command) error
+
+	// UnregisterCommand unregisters a command previously registered via RegisterCommand.
+	UnregisterCommand(teamId, trigger string) error
+
 	// CreateUser creates a user.
 	CreateUser(user *model.User) (*model.User, *model.AppError)
 
diff --git a/plugin/hooks.go b/plugin/hooks.go
index 04d5c7c14..814609e8c 100644
--- a/plugin/hooks.go
+++ b/plugin/hooks.go
@@ -5,6 +5,8 @@ package plugin
 
 import (
 	"net/http"
+
+	"github.com/mattermost/mattermost-server/model"
 )
 
 // Methods from the Hooks interface can be used by a plugin to respond to events. Methods are likely
@@ -30,4 +32,8 @@ type Hooks interface {
 	// The Mattermost-User-Id header will be present if (and only if) the request is by an
 	// authenticated user.
 	ServeHTTP(http.ResponseWriter, *http.Request)
+
+	// ExecuteCommand executes a command that has been previously registered via the RegisterCommand
+	// API.
+	ExecuteCommand(args *model.CommandArgs) (*model.CommandResponse, *model.AppError)
 }
diff --git a/plugin/pluginenv/environment.go b/plugin/pluginenv/environment.go
index 26511c651..f53021f74 100644
--- a/plugin/pluginenv/environment.go
+++ b/plugin/pluginenv/environment.go
@@ -223,35 +223,59 @@ func (env *Environment) Shutdown() (errs []error) {
 	return
 }
 
-type EnvironmentHooks struct {
+type MultiPluginHooks struct {
 	env *Environment
 }
 
-func (env *Environment) Hooks() *EnvironmentHooks {
-	return &EnvironmentHooks{env}
+type SinglePluginHooks struct {
+	env      *Environment
+	pluginId string
 }
 
-// OnConfigurationChange invokes the OnConfigurationChange hook for all plugins. Any errors
-// encountered will be returned.
-func (h *EnvironmentHooks) OnConfigurationChange() (errs []error) {
+func (env *Environment) Hooks() *MultiPluginHooks {
+	return &MultiPluginHooks{
+		env: env,
+	}
+}
+
+func (env *Environment) HooksForPlugin(id string) *SinglePluginHooks {
+	return &SinglePluginHooks{
+		env:      env,
+		pluginId: id,
+	}
+}
+
+func (h *MultiPluginHooks) invoke(f func(plugin.Hooks) error) (errs []error) {
 	h.env.mutex.RLock()
 	defer h.env.mutex.RUnlock()
+
 	for _, activePlugin := range h.env.activePlugins {
 		if activePlugin.Supervisor == nil {
 			continue
 		}
-		if err := activePlugin.Supervisor.Hooks().OnConfigurationChange(); err != nil {
-			errs = append(errs, errors.Wrapf(err, "OnConfigurationChange error for %v", activePlugin.BundleInfo.Manifest.Id))
+		if err := f(activePlugin.Supervisor.Hooks()); err != nil {
+			errs = append(errs, errors.Wrapf(err, "hook error for %v", activePlugin.BundleInfo.Manifest.Id))
 		}
 	}
 	return
 }
 
+// OnConfigurationChange invokes the OnConfigurationChange hook for all plugins. Any errors
+// encountered will be returned.
+func (h *MultiPluginHooks) OnConfigurationChange() []error {
+	return h.invoke(func(hooks plugin.Hooks) error {
+		if err := hooks.OnConfigurationChange(); err != nil {
+			return errors.Wrapf(err, "error calling OnConfigurationChange hook")
+		}
+		return nil
+	})
+}
+
 // ServeHTTP invokes the ServeHTTP hook for the plugin identified by the request or responds with a
 // 404 not found.
 //
 // It expects the request's context to have a plugin_id set.
-func (h *EnvironmentHooks) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+func (h *MultiPluginHooks) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	if id := r.Context().Value("plugin_id"); id != nil {
 		if idstr, ok := id.(string); ok {
 			h.env.mutex.RLock()
@@ -264,3 +288,25 @@ func (h *EnvironmentHooks) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	}
 	http.NotFound(w, r)
 }
+
+func (h *SinglePluginHooks) invoke(f func(plugin.Hooks) error) error {
+	h.env.mutex.RLock()
+	defer h.env.mutex.RUnlock()
+
+	if activePlugin, ok := h.env.activePlugins[h.pluginId]; ok && activePlugin.Supervisor != nil {
+		if err := f(activePlugin.Supervisor.Hooks()); err != nil {
+			return errors.Wrapf(err, "hook error for plugin: %v", activePlugin.BundleInfo.Manifest.Id)
+		}
+		return nil
+	}
+	return fmt.Errorf("unable to invoke hook for plugin: %v", h.pluginId)
+}
+
+// ExecuteCommand invokes the ExecuteCommand hook for the plugin.
+func (h *SinglePluginHooks) ExecuteCommand(args *model.CommandArgs) (resp *model.CommandResponse, appErr *model.AppError, err error) {
+	err = h.invoke(func(hooks plugin.Hooks) error {
+		resp, appErr = hooks.ExecuteCommand(args)
+		return nil
+	})
+	return
+}
diff --git a/plugin/pluginenv/environment_test.go b/plugin/pluginenv/environment_test.go
index 988e5b08f..2a52b3830 100644
--- a/plugin/pluginenv/environment_test.go
+++ b/plugin/pluginenv/environment_test.go
@@ -355,3 +355,51 @@ func TestEnvironment_ConcurrentHookInvocations(t *testing.T) {
 
 	wg.Wait()
 }
+
+func TestEnvironment_HooksForPlugins(t *testing.T) {
+	dir := initTmpDir(t, map[string]string{
+		"foo/plugin.json": `{"id": "foo", "backend": {}}`,
+	})
+	defer os.RemoveAll(dir)
+
+	var provider MockProvider
+	defer provider.AssertExpectations(t)
+
+	env, err := New(
+		SearchPath(dir),
+		APIProvider(provider.API),
+		SupervisorProvider(provider.Supervisor),
+	)
+	require.NoError(t, err)
+	defer env.Shutdown()
+
+	var api struct{ plugin.API }
+	var supervisor MockSupervisor
+	defer supervisor.AssertExpectations(t)
+	var hooks plugintest.Hooks
+	defer hooks.AssertExpectations(t)
+
+	provider.On("API").Return(&api, nil)
+	provider.On("Supervisor").Return(&supervisor, nil)
+
+	supervisor.On("Start", &api).Return(nil)
+	supervisor.On("Stop").Return(nil)
+	supervisor.On("Hooks").Return(&hooks)
+
+	hooks.On("OnDeactivate").Return(nil)
+	hooks.On("ExecuteCommand", mock.AnythingOfType("*model.CommandArgs")).Return(&model.CommandResponse{
+		Text: "bar",
+	}, nil)
+
+	assert.NoError(t, env.ActivatePlugin("foo"))
+	assert.Equal(t, env.ActivePluginIds(), []string{"foo"})
+
+	resp, appErr, err := env.HooksForPlugin("foo").ExecuteCommand(&model.CommandArgs{
+		Command: "/foo",
+	})
+	assert.Equal(t, "bar", resp.Text)
+	assert.Nil(t, appErr)
+	assert.NoError(t, err)
+
+	assert.Empty(t, env.Shutdown())
+}
diff --git a/plugin/plugintest/api.go b/plugin/plugintest/api.go
index b00542032..75174a9a6 100644
--- a/plugin/plugintest/api.go
+++ b/plugin/plugintest/api.go
@@ -30,6 +30,22 @@ func (m *API) LoadPluginConfiguration(dest interface{}) error {
 	return ret.Error(0)
 }
 
+func (m *API) RegisterCommand(command *model.Command) error {
+	ret := m.Called(command)
+	if f, ok := ret.Get(0).(func(*model.Command) error); ok {
+		return f(command)
+	}
+	return ret.Error(0)
+}
+
+func (m *API) UnregisterCommand(teamId, trigger string) error {
+	ret := m.Called(teamId, trigger)
+	if f, ok := ret.Get(0).(func(string, string) error); ok {
+		return f(teamId, trigger)
+	}
+	return ret.Error(0)
+}
+
 func (m *API) CreateUser(user *model.User) (*model.User, *model.AppError) {
 	ret := m.Called(user)
 	if f, ok := ret.Get(0).(func(*model.User) (*model.User, *model.AppError)); ok {
diff --git a/plugin/plugintest/hooks.go b/plugin/plugintest/hooks.go
index 56d048d6a..9ea11a9fb 100644
--- a/plugin/plugintest/hooks.go
+++ b/plugin/plugintest/hooks.go
@@ -8,6 +8,7 @@ import (
 
 	"github.com/stretchr/testify/mock"
 
+	"github.com/mattermost/mattermost-server/model"
 	"github.com/mattermost/mattermost-server/plugin"
 )
 
@@ -18,7 +19,11 @@ type Hooks struct {
 var _ plugin.Hooks = (*Hooks)(nil)
 
 func (m *Hooks) OnActivate(api plugin.API) error {
-	return m.Called(api).Error(0)
+	ret := m.Called(api)
+	if f, ok := ret.Get(0).(func(plugin.API) error); ok {
+		return f(api)
+	}
+	return ret.Error(0)
 }
 
 func (m *Hooks) OnDeactivate() error {
@@ -32,3 +37,13 @@ func (m *Hooks) OnConfigurationChange() error {
 func (m *Hooks) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	m.Called(w, r)
 }
+
+func (m *Hooks) ExecuteCommand(args *model.CommandArgs) (*model.CommandResponse, *model.AppError) {
+	ret := m.Called(args)
+	if f, ok := ret.Get(0).(func(*model.CommandArgs) (*model.CommandResponse, *model.AppError)); ok {
+		return f(args)
+	}
+	resp, _ := ret.Get(0).(*model.CommandResponse)
+	err, _ := ret.Get(1).(*model.AppError)
+	return resp, err
+}
diff --git a/plugin/rpcplugin/api.go b/plugin/rpcplugin/api.go
index 76c6e3039..5b5b11a62 100644
--- a/plugin/rpcplugin/api.go
+++ b/plugin/rpcplugin/api.go
@@ -32,6 +32,14 @@ func (api *LocalAPI) LoadPluginConfiguration(args struct{}, reply *[]byte) error
 	return nil
 }
 
+func (api *LocalAPI) RegisterCommand(args *model.Command, reply *APITeamReply) error {
+	return api.api.RegisterCommand(args)
+}
+
+func (api *LocalAPI) UnregisterCommand(args *APIUnregisterCommandArgs, reply *APITeamReply) error {
+	return api.api.UnregisterCommand(args.TeamId, args.Trigger)
+}
+
 type APIErrorReply struct {
 	Error *model.AppError
 }
@@ -344,6 +352,22 @@ func (api *RemoteAPI) LoadPluginConfiguration(dest interface{}) error {
 	return json.Unmarshal(config, dest)
 }
 
+func (api *RemoteAPI) RegisterCommand(command *model.Command) error {
+	return api.client.Call("LocalAPI.RegisterCommand", command, nil)
+}
+
+type APIUnregisterCommandArgs struct {
+	TeamId  string
+	Trigger string
+}
+
+func (api *RemoteAPI) UnregisterCommand(teamId, trigger string) error {
+	return api.client.Call("LocalAPI.UnregisterCommand", &APIUnregisterCommandArgs{
+		TeamId:  teamId,
+		Trigger: trigger,
+	}, nil)
+}
+
 func (api *RemoteAPI) CreateUser(user *model.User) (*model.User, *model.AppError) {
 	var reply APIUserReply
 	if err := api.client.Call("LocalAPI.CreateUser", user, &reply); err != nil {
diff --git a/plugin/rpcplugin/api_test.go b/plugin/rpcplugin/api_test.go
index f9e474d4a..145ec9005 100644
--- a/plugin/rpcplugin/api_test.go
+++ b/plugin/rpcplugin/api_test.go
@@ -2,6 +2,7 @@ package rpcplugin
 
 import (
 	"encoding/json"
+	"fmt"
 	"io"
 	"net/http"
 	"testing"
@@ -84,6 +85,16 @@ func TestAPI(t *testing.T) {
 		assert.Equal(t, "foo", config.Foo)
 		assert.Equal(t, "baz", config.Bar.Baz)
 
+		api.On("RegisterCommand", mock.AnythingOfType("*model.Command")).Return(fmt.Errorf("foo")).Once()
+		assert.Error(t, remote.RegisterCommand(&model.Command{}))
+		api.On("RegisterCommand", mock.AnythingOfType("*model.Command")).Return(nil).Once()
+		assert.NoError(t, remote.RegisterCommand(&model.Command{}))
+
+		api.On("UnregisterCommand", "team", "trigger").Return(fmt.Errorf("foo")).Once()
+		assert.Error(t, remote.UnregisterCommand("team", "trigger"))
+		api.On("UnregisterCommand", "team", "trigger").Return(nil).Once()
+		assert.NoError(t, remote.UnregisterCommand("team", "trigger"))
+
 		api.On("CreateChannel", mock.AnythingOfType("*model.Channel")).Return(func(c *model.Channel) (*model.Channel, *model.AppError) {
 			c.Id = "thechannelid"
 			return c, nil
diff --git a/plugin/rpcplugin/hooks.go b/plugin/rpcplugin/hooks.go
index 22f26e22e..7b44d0de7 100644
--- a/plugin/rpcplugin/hooks.go
+++ b/plugin/rpcplugin/hooks.go
@@ -11,6 +11,7 @@ import (
 	"net/rpc"
 	"reflect"
 
+	"github.com/mattermost/mattermost-server/model"
 	"github.com/mattermost/mattermost-server/plugin"
 )
 
@@ -125,6 +126,20 @@ func (h *LocalHooks) ServeHTTP(args ServeHTTPArgs, reply *struct{}) error {
 	return nil
 }
 
+type HooksExecuteCommandReply struct {
+	Response *model.CommandResponse
+	Error    *model.AppError
+}
+
+func (h *LocalHooks) ExecuteCommand(args *model.CommandArgs, reply *HooksExecuteCommandReply) error {
+	if hook, ok := h.hooks.(interface {
+		ExecuteCommand(*model.CommandArgs) (*model.CommandResponse, *model.AppError)
+	}); ok {
+		reply.Response, reply.Error = hook.ExecuteCommand(args)
+	}
+	return nil
+}
+
 func ServeHooks(hooks interface{}, conn io.ReadWriteCloser, muxer *Muxer) {
 	server := rpc.NewServer()
 	server.Register(&LocalHooks{
@@ -141,6 +156,7 @@ const (
 	remoteOnDeactivate          = 1
 	remoteServeHTTP             = 2
 	remoteOnConfigurationChange = 3
+	remoteExecuteCommand        = 4
 	maxRemoteHookCount          = iota
 )
 
@@ -225,6 +241,17 @@ func (h *RemoteHooks) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	}
 }
 
+func (h *RemoteHooks) ExecuteCommand(args *model.CommandArgs) (*model.CommandResponse, *model.AppError) {
+	if !h.implemented[remoteExecuteCommand] {
+		return nil, model.NewAppError("RemoteHooks.ExecuteCommand", "plugin.rpcplugin.invocation.error", nil, "err=ExecuteCommand hook not implemented", http.StatusInternalServerError)
+	}
+	var reply HooksExecuteCommandReply
+	if err := h.client.Call("LocalHooks.ExecuteCommand", args, &reply); err != nil {
+		return nil, model.NewAppError("RemoteHooks.ExecuteCommand", "plugin.rpcplugin.invocation.error", nil, "err="+err.Error(), http.StatusInternalServerError)
+	}
+	return reply.Response, reply.Error
+}
+
 func (h *RemoteHooks) Close() error {
 	if h.apiCloser != nil {
 		h.apiCloser.Close()
@@ -253,6 +280,8 @@ func ConnectHooks(conn io.ReadWriteCloser, muxer *Muxer) (*RemoteHooks, error) {
 			remote.implemented[remoteOnConfigurationChange] = true
 		case "ServeHTTP":
 			remote.implemented[remoteServeHTTP] = true
+		case "ExecuteCommand":
+			remote.implemented[remoteExecuteCommand] = true
 		}
 	}
 	return remote, nil
diff --git a/plugin/rpcplugin/hooks_test.go b/plugin/rpcplugin/hooks_test.go
index 37c529510..116038dae 100644
--- a/plugin/rpcplugin/hooks_test.go
+++ b/plugin/rpcplugin/hooks_test.go
@@ -13,6 +13,7 @@ import (
 	"github.com/stretchr/testify/mock"
 	"github.com/stretchr/testify/require"
 
+	"github.com/mattermost/mattermost-server/model"
 	"github.com/mattermost/mattermost-server/plugin"
 	"github.com/mattermost/mattermost-server/plugin/plugintest"
 )
@@ -79,6 +80,17 @@ func TestHooks(t *testing.T) {
 		body, err := ioutil.ReadAll(resp.Body)
 		assert.NoError(t, err)
 		assert.Equal(t, "bar", string(body))
+
+		hooks.On("ExecuteCommand", &model.CommandArgs{
+			Command: "/foo",
+		}).Return(&model.CommandResponse{
+			Text: "bar",
+		}, nil)
+		commandResponse, appErr := hooks.ExecuteCommand(&model.CommandArgs{
+			Command: "/foo",
+		})
+		assert.Equal(t, "bar", commandResponse.Text)
+		assert.Nil(t, appErr)
 	}))
 }