services.go

// -*- Mode: Go; indent-tabs-mode: t -*-

/*
 * Copyright (C) 2014-2016 Canonical Ltd
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 3 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 */

package wrappers

import (
	"bytes"
	"context"
	"fmt"
	"os"
	"path/filepath"
	"sort"
	"strconv"
	"strings"
	"text/template"
	"time"

	"github.com/snapcore/snapd/dirs"
	"github.com/snapcore/snapd/logger"
	"github.com/snapcore/snapd/osutil"
	"github.com/snapcore/snapd/osutil/sys"
	"github.com/snapcore/snapd/progress"
	"github.com/snapcore/snapd/randutil"
	"github.com/snapcore/snapd/snap"
	"github.com/snapcore/snapd/strutil"
	"github.com/snapcore/snapd/systemd"
	"github.com/snapcore/snapd/timeout"
	"github.com/snapcore/snapd/timeutil"
	"github.com/snapcore/snapd/timings"
	"github.com/snapcore/snapd/usersession/client"
)

type interacter interface {
	Notify(status string)
}

// wait this time between TERM and KILL
var killWait = 5 * time.Second

func serviceStopTimeout(app *snap.AppInfo) time.Duration {
	tout := app.StopTimeout
	if tout == 0 {
		tout = timeout.DefaultTimeout
	}
	return time.Duration(tout)
}

func generateSnapServiceFile(app *snap.AppInfo, opts *AddSnapServicesOptions) ([]byte, error) {
	if err := snap.ValidateApp(app); err != nil {
		return nil, err
	}

	return genServiceFile(app, opts), nil
}

func stopUserServices(cli *client.Client, inter interacter, services ...string) error {
	ctx, cancel := context.WithTimeout(context.Background(), time.Duration(timeout.DefaultTimeout))
	defer cancel()
	failures, err := cli.ServicesStop(ctx, services)
	for _, f := range failures {
		inter.Notify(fmt.Sprintf("Could not stop service %q for uid %d: %s", f.Service, f.Uid, f.Error))
	}
	return err
}

func startUserServices(cli *client.Client, inter interacter, services ...string) error {
	ctx, cancel := context.WithTimeout(context.Background(), time.Duration(timeout.DefaultTimeout))
	defer cancel()
	startFailures, stopFailures, err := cli.ServicesStart(ctx, services)
	for _, f := range startFailures {
		inter.Notify(fmt.Sprintf("Could not start service %q for uid %d: %s", f.Service, f.Uid, f.Error))
	}
	for _, f := range stopFailures {
		inter.Notify(fmt.Sprintf("While trying to stop previously started service %q for uid %d: %s", f.Service, f.Uid, f.Error))
	}
	return err
}

func stopService(sysd systemd.Systemd, app *snap.AppInfo, inter interacter) error {
	serviceName := app.ServiceName()
	tout := serviceStopTimeout(app)

	var extraServices []string
	for _, socket := range app.Sockets {
		extraServices = append(extraServices, filepath.Base(socket.File()))
	}
	if app.Timer != nil {
		extraServices = append(extraServices, filepath.Base(app.Timer.File()))
	}

	switch app.DaemonScope {
	case snap.SystemDaemon:
		stopErrors := []error{}
		for _, service := range extraServices {
			if err := sysd.Stop(service, tout); err != nil {
				stopErrors = append(stopErrors, err)
			}
		}

		if err := sysd.Stop(serviceName, tout); err != nil {
			if !systemd.IsTimeout(err) {
				return err
			}
			inter.Notify(fmt.Sprintf("%s refused to stop, killing.", serviceName))
			// ignore errors for kill; nothing we'd do differently at this point
			sysd.Kill(serviceName, "TERM", "")
			time.Sleep(killWait)
			sysd.Kill(serviceName, "KILL", "")
		}

		if len(stopErrors) > 0 {
			return stopErrors[0]
		}

	case snap.UserDaemon:
		extraServices = append(extraServices, serviceName)
		cli := client.New()
		return stopUserServices(cli, inter, extraServices...)
	}

	return nil
}

// StartServices starts service units for the applications from the snap which
// are services. Service units will be started in the order provided by the
// caller.
func StartServices(apps []*snap.AppInfo, inter interacter, tm timings.Measurer) (err error) {
	systemSysd := systemd.New(dirs.GlobalRootDir, systemd.SystemMode, inter)
	userSysd := systemd.New(dirs.GlobalRootDir, systemd.GlobalUserMode, inter)
	cli := client.New()

	systemServices := make([]string, 0, len(apps))
	userServices := make([]string, 0, len(apps))
	for _, app := range apps {
		// they're *supposed* to be all services, but checking doesn't hurt
		if !app.IsService() {
			continue
		}

		var sysd systemd.Systemd
		switch app.DaemonScope {
		case snap.SystemDaemon:
			sysd = systemSysd
		case snap.UserDaemon:
			sysd = userSysd
		}

		defer func(app *snap.AppInfo) {
			if err == nil {
				return
			}
			if e := stopService(sysd, app, inter); e != nil {
				inter.Notify(fmt.Sprintf("While trying to stop previously started service %q: %v", app.ServiceName(), e))
			}
			for _, socket := range app.Sockets {
				socketService := filepath.Base(socket.File())
				if e := sysd.Disable(socketService); e != nil {
					inter.Notify(fmt.Sprintf("While trying to disable previously enabled socket service %q: %v", socketService, e))
				}
			}
			if app.Timer != nil {
				timerService := filepath.Base(app.Timer.File())
				if e := sysd.Disable(timerService); e != nil {
					inter.Notify(fmt.Sprintf("While trying to disable previously enabled timer service %q: %v", timerService, e))
				}
			}
		}(app)

		if len(app.Sockets) == 0 && app.Timer == nil && app.Daemon != "dbus" {
			// check if the service is disabled, if so don't start it up
			// this could happen for example if the service was disabled in
			// the install hook by snapctl or if the service was disabled in
			// the previous installation
			isEnabled, err := sysd.IsEnabled(app.ServiceName())
			if err != nil {
				return err
			}
			if isEnabled {
				switch app.DaemonScope {
				case snap.SystemDaemon:
					systemServices = append(systemServices, app.ServiceName())
				case snap.UserDaemon:
					userServices = append(userServices, app.ServiceName())
				}
			}
		}

		for _, socket := range app.Sockets {
			socketService := filepath.Base(socket.File())
			// enable the socket
			if err := sysd.Enable(socketService); err != nil {
				return err
			}

			switch app.DaemonScope {
			case snap.SystemDaemon:
				timings.Run(tm, "start-system-socket-service", fmt.Sprintf("start system socket service %q", socketService), func(nested timings.Measurer) {
					err = sysd.Start(socketService)
				})
			case snap.UserDaemon:
				timings.Run(tm, "start-user-socket-service", fmt.Sprintf("start user socket service %q", socketService), func(nested timings.Measurer) {
					err = startUserServices(cli, inter, socketService)
				})
			}
			if err != nil {
				return err
			}
		}

		if app.Timer != nil {
			timerService := filepath.Base(app.Timer.File())
			// enable the timer
			if err := sysd.Enable(timerService); err != nil {
				return err
			}

			switch app.DaemonScope {
			case snap.SystemDaemon:
				timings.Run(tm, "start-system-timer-service", fmt.Sprintf("start system timer service %q", timerService), func(nested timings.Measurer) {
					err = sysd.Start(timerService)
				})
			case snap.UserDaemon:
				timings.Run(tm, "start-user-timer-service", fmt.Sprintf("start user timer service %q", timerService), func(nested timings.Measurer) {
					err = startUserServices(cli, inter, timerService)
				})
			}
			if err != nil {
				return err
			}
		}
	}

	for _, srv := range systemServices {
		// starting all services at once does not create a single
		// transaction, but instead spawns multiple jobs, make sure the
		// services started in the original order by bring them up one
		// by one, see:
		// https://github.com/systemd/systemd/issues/8102
		// https://lists.freedesktop.org/archives/systemd-devel/2018-January/040152.html
		timings.Run(tm, "start-service", fmt.Sprintf("start service %q", srv), func(nested timings.Measurer) {
			err = systemSysd.Start(srv)
		})
		if err != nil {
			// cleanup was set up by iterating over apps
			return err
		}
	}
	if len(userServices) != 0 {
		timings.Run(tm, "start-user-services", "start user services", func(nested timings.Measurer) {
			err = startUserServices(cli, inter, userServices...)
		})
		if err != nil {
			return err
		}
	}

	return nil
}

func userDaemonReload() error {
	cli := client.New()
	ctx, cancel := context.WithTimeout(context.Background(), time.Duration(timeout.DefaultTimeout))
	defer cancel()
	return cli.ServicesDaemonReload(ctx)
}

type AddSnapServicesOptions struct {
	Preseeding   bool
	VitalityRank int
}

// AddSnapServices adds service units for the applications from the snap which are services.
func AddSnapServices(s *snap.Info, disabledSvcs []string, opts *AddSnapServicesOptions, inter interacter) (err error) {
	if s.GetType() == snap.TypeSnapd {
		return fmt.Errorf("internal error: adding explicit services for snapd snap is unexpected")
	}

	if opts == nil {
		opts = &AddSnapServicesOptions{}
	}

	// check if any previously disabled services are now no longer services and
	// log messages about that
	for _, svc := range disabledSvcs {
		app, ok := s.Apps[svc]
		if !ok {
			logger.Noticef("previously disabled service %s no longer exists", svc)
		} else if !app.IsService() {
			logger.Noticef("previously disabled service %s is now an app and not a service", svc)
		}
	}

	// TODO: remove once services get enabled on start and not when created.
	preseeding := opts.Preseeding

	sysd := systemd.New(dirs.GlobalRootDir, systemd.SystemMode, inter)
	userSysd := systemd.New(dirs.GlobalRootDir, systemd.GlobalUserMode, inter)
	var written []string
	var writtenSystem, writtenUser bool
	var enabled []string
	var userEnabled []string
	defer func() {
		if err == nil {
			return
		}
		for _, s := range enabled {
			if e := sysd.Disable(s); e != nil {
				inter.Notify(fmt.Sprintf("while trying to disable %s due to previous failure: %v", s, e))
			}
		}
		for _, s := range userEnabled {
			if e := userSysd.Disable(s); e != nil {
				inter.Notify(fmt.Sprintf("while trying to disable %s due to previous failure: %v", s, e))
			}
		}
		for _, s := range written {
			if e := os.Remove(s); e != nil {
				inter.Notify(fmt.Sprintf("while trying to remove %s due to previous failure: %v", s, e))
			}
		}
		if writtenSystem && !preseeding {
			if e := sysd.DaemonReload(); e != nil {
				inter.Notify(fmt.Sprintf("while trying to perform systemd daemon-reload due to previous failure: %v", e))
			}
		}
		if writtenUser && !preseeding {
			if e := userDaemonReload(); e != nil {
				inter.Notify(fmt.Sprintf("while trying to perform user systemd daemon-reload due to previous failure: %v", e))
			}
		}
	}()

	for _, app := range s.Apps {
		if !app.IsService() {
			continue
		}
		// Generate service file
		content, err := generateSnapServiceFile(app, opts)
		if err != nil {
			return err
		}
		svcFilePath := app.ServiceFile()
		os.MkdirAll(filepath.Dir(svcFilePath), 0755)
		if err := osutil.AtomicWriteFile(svcFilePath, content, 0644, 0); err != nil {
			return err
		}
		written = append(written, svcFilePath)
		switch app.DaemonScope {
		case snap.SystemDaemon:
			writtenSystem = true
		case snap.UserDaemon:
			writtenUser = true
		}

		// Generate systemd .socket files if needed
		socketFiles, err := generateSnapSocketFiles(app)
		if err != nil {
			return err
		}
		for path, content := range *socketFiles {
			os.MkdirAll(filepath.Dir(path), 0755)
			if err := osutil.AtomicWriteFile(path, content, 0644, 0); err != nil {
				return err
			}
			written = append(written, path)
		}

		if app.Timer != nil {
			content, err := generateSnapTimerFile(app)
			if err != nil {
				return err
			}
			path := app.Timer.File()
			os.MkdirAll(filepath.Dir(path), 0755)
			if err := osutil.AtomicWriteFile(path, content, 0644, 0); err != nil {
				return err
			}
			written = append(written, path)
		}

		if app.Timer != nil || len(app.Sockets) != 0 || app.Daemon == "dbus" {
			// service is dbus, socket, or timer activated,
			// not during the boot
			continue
		}

		svcName := app.ServiceName()
		switch app.DaemonScope {
		case snap.SystemDaemon:
			if strutil.ListContains(disabledSvcs, app.Name) {
				// service is disabled, nothing to do
				continue
			}

			if !preseeding {
				if err := sysd.Enable(svcName); err != nil {
					return err
				}
				enabled = append(enabled, svcName)
			}
		case snap.UserDaemon:
			if !preseeding {
				if err := userSysd.Enable(svcName); err != nil {
					return err
				}
				userEnabled = append(userEnabled, svcName)
			}
		}
	}

	if !preseeding {
		if writtenSystem {
			if err := sysd.DaemonReload(); err != nil {
				return err
			}
		}
		if writtenUser {
			if err := userDaemonReload(); err != nil {
				return err
			}
		}
	}

	return nil
}

// EnableSnapServices enables all services of the snap; the main use case for this is
// the first boot of a pre-seeded image with service files already in place but not enabled.
// XXX: it should go away once services are fixed and enabled on start.
func EnableSnapServices(s *snap.Info, inter interacter) (err error) {
	sysd := systemd.New(dirs.GlobalRootDir, systemd.SystemMode, inter)
	for _, app := range s.Apps {
		if app.IsService() {
			svcName := app.ServiceName()
			if err := sysd.Enable(svcName); err != nil {
				return err
			}
		}
	}
	return nil
}

// StopServices stops service units for the applications from the snap which are services.
func StopServices(apps []*snap.AppInfo, reason snap.ServiceStopReason, inter interacter, tm timings.Measurer) error {
	sysd := systemd.New(dirs.GlobalRootDir, systemd.SystemMode, inter)

	logger.Debugf("StopServices called for %q, reason: %v", apps, reason)
	for _, app := range apps {
		// Handle the case where service file doesn't exist and don't try to stop it as it will fail.
		// This can happen with snap try when snap.yaml is modified on the fly and a daemon line is added.
		if !app.IsService() || !osutil.FileExists(app.ServiceFile()) {
			continue
		}
		// Skip stop on refresh when refresh mode is set to something
		// other than "restart" (or "" which is the same)
		if reason == snap.StopReasonRefresh {
			logger.Debugf(" %s refresh-mode: %v", app.Name, app.StopMode)
			switch app.RefreshMode {
			case "endure":
				// skip this service
				continue
			}
		}

		var err error
		timings.Run(tm, "stop-service", fmt.Sprintf("stop service %q", app.ServiceName()), func(nested timings.Measurer) {
			err = stopService(sysd, app, inter)
		})
		if err != nil {
			return err
		}

		// ensure the service is really stopped on remove regardless
		// of stop-mode
		if reason == snap.StopReasonRemove && !app.StopMode.KillAll() && app.DaemonScope == snap.SystemDaemon {
			// FIXME: make this smarter and avoid the killWait
			//        delay if not needed (i.e. if all processes
			//        have died)
			sysd.Kill(app.ServiceName(), "TERM", "all")
			time.Sleep(killWait)
			sysd.Kill(app.ServiceName(), "KILL", "")
		}
	}
	return nil
}

// ServicesEnableState returns a map of service names from the given snap,
// together with their enable/disable status.
func ServicesEnableState(s *snap.Info, inter interacter) (map[string]bool, error) {
	sysd := systemd.New(dirs.GlobalRootDir, systemd.SystemMode, inter)

	// loop over all services in the snap, querying systemd for the current
	// systemd state of the snaps
	snapSvcsState := make(map[string]bool, len(s.Apps))
	for name, app := range s.Apps {
		if !app.IsService() {
			continue
		}
		// FIXME: handle user daemons
		if app.DaemonScope != snap.SystemDaemon {
			continue
		}
		state, err := sysd.IsEnabled(app.ServiceName())
		if err != nil {
			return nil, err
		}
		snapSvcsState[name] = state
	}
	return snapSvcsState, nil
}

// RemoveSnapServices disables and removes service units for the applications
// from the snap which are services. The optional flag indicates whether
// services are removed as part of undoing of first install of a given snap.
func RemoveSnapServices(s *snap.Info, inter interacter) error {
	if s.GetType() == snap.TypeSnapd {
		return fmt.Errorf("internal error: removing explicit services for snapd snap is unexpected")
	}
	systemSysd := systemd.New(dirs.GlobalRootDir, systemd.SystemMode, inter)
	userSysd := systemd.New(dirs.GlobalRootDir, systemd.GlobalUserMode, inter)
	var removedSystem, removedUser bool

	for _, app := range s.Apps {
		if !app.IsService() || !osutil.FileExists(app.ServiceFile()) {
			continue
		}

		var sysd systemd.Systemd
		switch app.DaemonScope {
		case snap.SystemDaemon:
			sysd = systemSysd
			removedSystem = true
		case snap.UserDaemon:
			sysd = userSysd
			removedUser = true
		}
		serviceName := filepath.Base(app.ServiceFile())

		for _, socket := range app.Sockets {
			path := socket.File()
			socketServiceName := filepath.Base(path)
			if err := sysd.Disable(socketServiceName); err != nil {
				return err
			}

			if err := os.Remove(path); err != nil && !os.IsNotExist(err) {
				logger.Noticef("Failed to remove socket file %q for %q: %v", path, serviceName, err)
			}
		}

		if app.Timer != nil {
			path := app.Timer.File()

			timerName := filepath.Base(path)
			if err := sysd.Disable(timerName); err != nil {
				return err
			}

			if err := os.Remove(path); err != nil && !os.IsNotExist(err) {
				logger.Noticef("Failed to remove timer file %q for %q: %v", path, serviceName, err)
			}
		}

		if err := sysd.Disable(serviceName); err != nil {
			return err
		}

		if err := os.Remove(app.ServiceFile()); err != nil && !os.IsNotExist(err) {
			logger.Noticef("Failed to remove service file for %q: %v", serviceName, err)
		}

	}

	// only reload if we actually had services
	if removedSystem {
		if err := systemSysd.DaemonReload(); err != nil {
			return err
		}
	}
	if removedUser {
		if err := userDaemonReload(); err != nil {
			return err
		}
	}

	return nil
}

func genServiceNames(snap *snap.Info, appNames []string) []string {
	names := make([]string, 0, len(appNames))

	for _, name := range appNames {
		if app := snap.Apps[name]; app != nil {
			names = append(names, app.ServiceName())
		}
	}
	return names
}

func genServiceFile(appInfo *snap.AppInfo, opts *AddSnapServicesOptions) []byte {
	if opts == nil {
		opts = &AddSnapServicesOptions{}
	}

	serviceTemplate := `[Unit]
# Auto-generated, DO NOT EDIT
Description=Service for snap application {{.App.Snap.InstanceName}}.{{.App.Name}}
{{- if .MountUnit }}
Requires={{.MountUnit}}
{{- end }}
{{- if .PrerequisiteTarget}}
Wants={{.PrerequisiteTarget}}
{{- end}}
{{- if .After}}
After={{ stringsJoin .After " " }}
{{- end}}
{{- if .Before}}
Before={{ stringsJoin .Before " "}}
{{- end}}
X-Snappy=yes

[Service]
EnvironmentFile=-/etc/environment
ExecStart={{.App.LauncherCommand}}
SyslogIdentifier={{.App.Snap.InstanceName}}.{{.App.Name}}
Restart={{.Restart}}
{{- if .App.RestartDelay}}
RestartSec={{.App.RestartDelay.Seconds}}
{{- end}}
WorkingDirectory={{.WorkingDir}}
{{- if .App.StopCommand}}
ExecStop={{.App.LauncherStopCommand}}
{{- end}}
{{- if .App.ReloadCommand}}
ExecReload={{.App.LauncherReloadCommand}}
{{- end}}
{{- if .App.PostStopCommand}}
ExecStopPost={{.App.LauncherPostStopCommand}}
{{- end}}
{{- if .StopTimeout}}
TimeoutStopSec={{.StopTimeout.Seconds}}
{{- end}}
{{- if .StartTimeout}}
TimeoutStartSec={{.StartTimeout.Seconds}}
{{- end}}
Type={{.App.Daemon}}
{{- if .Remain}}
RemainAfterExit={{.Remain}}
{{- end}}
{{- if .BusName}}
BusName={{.BusName}}
{{- end}}
{{- if .App.WatchdogTimeout}}
WatchdogSec={{.App.WatchdogTimeout.Seconds}}
{{- end}}
{{- if .KillMode}}
KillMode={{.KillMode}}
{{- end}}
{{- if .KillSignal}}
KillSignal={{.KillSignal}}
{{- end}}
{{- if .OOMAdjustScore }}
OOMScoreAdjust={{.OOMAdjustScore}}
{{- end}}
{{- if not .App.Sockets}}

[Install]
WantedBy={{.ServicesTarget}}
{{- end}}
`
	var templateOut bytes.Buffer
	tmpl := template.New("service-wrapper")
	tmpl.Funcs(template.FuncMap{
		"stringsJoin": strings.Join,
	})
	t := template.Must(tmpl.Parse(serviceTemplate))

	restartCond := appInfo.RestartCond.String()
	if restartCond == "" {
		restartCond = snap.RestartOnFailure.String()
	}

	// use score -900+vitalityRank, where vitalityRank starts at 1
	// and considering snapd itself has OOMScoreAdjust=-900
	const baseOOMAdjustScore = -900
	var oomAdjustScore int
	if opts.VitalityRank > 0 {
		oomAdjustScore = baseOOMAdjustScore + opts.VitalityRank
	}

	var remain string
	if appInfo.Daemon == "oneshot" {
		// any restart condition other than "no" is invalid for oneshot daemons
		restartCond = "no"
		// If StopExec is present for a oneshot service than we also need
		// RemainAfterExit=yes
		if appInfo.StopCommand != "" {
			remain = "yes"
		}
	}
	var killMode string
	if !appInfo.StopMode.KillAll() {
		killMode = "process"
	}

	var busName string
	if appInfo.Daemon == "dbus" && len(appInfo.ActivatesOn) > 0 {
		slot := appInfo.ActivatesOn[len(appInfo.ActivatesOn)-1]
		if err := slot.Attr("name", &busName); err != nil {
			logger.Noticef("Cannot get 'name' attribute of dbus slot %q: %v", slot.Name, err)
		}
	}

	wrapperData := struct {
		App *snap.AppInfo

		Restart            string
		WorkingDir         string
		StopTimeout        time.Duration
		StartTimeout       time.Duration
		ServicesTarget     string
		PrerequisiteTarget string
		MountUnit          string
		Remain             string
		KillMode           string
		KillSignal         string
		OOMAdjustScore     int
		BusName            string
		Before             []string
		After              []string

		Home    string
		EnvVars string
	}{
		App: appInfo,

		Restart:        restartCond,
		StopTimeout:    serviceStopTimeout(appInfo),
		StartTimeout:   time.Duration(appInfo.StartTimeout),
		Remain:         remain,
		KillMode:       killMode,
		KillSignal:     appInfo.StopMode.KillSignal(),
		OOMAdjustScore: oomAdjustScore,
		BusName:        busName,

		Before: genServiceNames(appInfo.Snap, appInfo.Before),
		After:  genServiceNames(appInfo.Snap, appInfo.After),

		// systemd runs as PID 1 so %h will not work.
		Home: "/root",
	}
	switch appInfo.DaemonScope {
	case snap.SystemDaemon:
		wrapperData.ServicesTarget = systemd.ServicesTarget
		wrapperData.PrerequisiteTarget = systemd.PrerequisiteTarget
		wrapperData.MountUnit = filepath.Base(systemd.MountUnitPath(appInfo.Snap.MountDir()))
		wrapperData.WorkingDir = appInfo.Snap.DataDir()
		wrapperData.After = append(wrapperData.After, "snapd.apparmor.service")
	case snap.UserDaemon:
		wrapperData.ServicesTarget = systemd.UserServicesTarget
		// FIXME: ideally use UserDataDir("%h"), but then the
		// unit fails if the directory doesn't exist.
		wrapperData.WorkingDir = appInfo.Snap.DataDir()
	default:
		panic("unknown snap.DaemonScope")
	}

	// Add extra "After" targets
	if wrapperData.PrerequisiteTarget != "" {
		wrapperData.After = append([]string{wrapperData.PrerequisiteTarget}, wrapperData.After...)
	}
	if wrapperData.MountUnit != "" {
		wrapperData.After = append([]string{wrapperData.MountUnit}, wrapperData.After...)
	}

	if err := t.Execute(&templateOut, wrapperData); err != nil {
		// this can never happen, except we forget a variable
		logger.Panicf("Unable to execute template: %v", err)
	}

	return templateOut.Bytes()
}

func genServiceSocketFile(appInfo *snap.AppInfo, socketName string) []byte {
	socketTemplate := `[Unit]
# Auto-generated, DO NOT EDIT
Description=Socket {{.SocketName}} for snap application {{.App.Snap.InstanceName}}.{{.App.Name}}
{{- if .MountUnit}}
Requires={{.MountUnit}}
After={{.MountUnit}}
{{- end}}
X-Snappy=yes

[Socket]
Service={{.ServiceFileName}}
FileDescriptorName={{.SocketInfo.Name}}
ListenStream={{.ListenStream}}
{{- if .SocketInfo.SocketMode}}
SocketMode={{.SocketInfo.SocketMode | printf "%04o"}}
{{- end}}

[Install]
WantedBy={{.SocketsTarget}}
`
	var templateOut bytes.Buffer
	t := template.Must(template.New("socket-wrapper").Parse(socketTemplate))

	socket := appInfo.Sockets[socketName]
	listenStream := renderListenStream(socket)
	wrapperData := struct {
		App             *snap.AppInfo
		ServiceFileName string
		SocketsTarget   string
		MountUnit       string
		SocketName      string
		SocketInfo      *snap.SocketInfo
		ListenStream    string
	}{
		App:             appInfo,
		ServiceFileName: filepath.Base(appInfo.ServiceFile()),
		SocketsTarget:   systemd.SocketsTarget,
		SocketName:      socketName,
		SocketInfo:      socket,
		ListenStream:    listenStream,
	}
	switch appInfo.DaemonScope {
	case snap.SystemDaemon:
		wrapperData.MountUnit = filepath.Base(systemd.MountUnitPath(appInfo.Snap.MountDir()))
	case snap.UserDaemon:
		// nothing
	default:
		panic("unknown snap.DaemonScope")
	}

	if err := t.Execute(&templateOut, wrapperData); err != nil {
		// this can never happen, except we forget a variable
		logger.Panicf("Unable to execute template: %v", err)
	}

	return templateOut.Bytes()
}

func generateSnapSocketFiles(app *snap.AppInfo) (*map[string][]byte, error) {
	if err := snap.ValidateApp(app); err != nil {
		return nil, err
	}

	socketFiles := make(map[string][]byte)
	for name, socket := range app.Sockets {
		socketFiles[socket.File()] = genServiceSocketFile(app, name)
	}
	return &socketFiles, nil
}

func renderListenStream(socket *snap.SocketInfo) string {
	s := socket.App.Snap
	listenStream := socket.ListenStream
	switch socket.App.DaemonScope {
	case snap.SystemDaemon:
		listenStream = strings.Replace(listenStream, "$SNAP_DATA", s.DataDir(), -1)
		// TODO: when we support User/Group in the generated
		// systemd unit, adjust this accordingly
		serviceUserUid := sys.UserID(0)
		runtimeDir := s.UserXdgRuntimeDir(serviceUserUid)
		listenStream = strings.Replace(listenStream, "$XDG_RUNTIME_DIR", runtimeDir, -1)
		listenStream = strings.Replace(listenStream, "$SNAP_COMMON", s.CommonDataDir(), -1)
	case snap.UserDaemon:
		listenStream = strings.Replace(listenStream, "$SNAP_USER_DATA", s.UserDataDir("%h"), -1)
		listenStream = strings.Replace(listenStream, "$SNAP_USER_COMMON", s.UserCommonDataDir("%h"), -1)
		// FIXME: find some way to share code with snap.UserXdgRuntimeDir()
		listenStream = strings.Replace(listenStream, "$XDG_RUNTIME_DIR", fmt.Sprintf("%%t/snap.%s", s.InstanceName()), -1)
	default:
		panic("unknown snap.DaemonScope")
	}
	return listenStream
}

func generateSnapTimerFile(app *snap.AppInfo) ([]byte, error) {
	timerTemplate := `[Unit]
# Auto-generated, DO NOT EDIT
Description=Timer {{.TimerName}} for snap application {{.App.Snap.InstanceName}}.{{.App.Name}}
{{- if .MountUnit}}
Requires={{.MountUnit}}
After={{.MountUnit}}
{{- end}}
X-Snappy=yes

[Timer]
Unit={{.ServiceFileName}}
{{ range .Schedules }}OnCalendar={{ . }}
{{ end }}
[Install]
WantedBy={{.TimersTarget}}
`
	var templateOut bytes.Buffer
	t := template.Must(template.New("timer-wrapper").Parse(timerTemplate))

	timerSchedule, err := timeutil.ParseSchedule(app.Timer.Timer)
	if err != nil {
		return nil, err
	}

	schedules := generateOnCalendarSchedules(timerSchedule)

	wrapperData := struct {
		App             *snap.AppInfo
		ServiceFileName string
		TimersTarget    string
		TimerName       string
		MountUnit       string
		Schedules       []string
	}{
		App:             app,
		ServiceFileName: filepath.Base(app.ServiceFile()),
		TimersTarget:    systemd.TimersTarget,
		TimerName:       app.Name,
		Schedules:       schedules,
	}
	switch app.DaemonScope {
	case snap.SystemDaemon:
		wrapperData.MountUnit = filepath.Base(systemd.MountUnitPath(app.Snap.MountDir()))
	case snap.UserDaemon:
		// nothing
	default:
		panic("unknown snap.DaemonScope")
	}

	if err := t.Execute(&templateOut, wrapperData); err != nil {
		// this can never happen, except we forget a variable
		logger.Panicf("Unable to execute template: %v", err)
	}

	return templateOut.Bytes(), nil
}

func makeAbbrevWeekdays(start time.Weekday, end time.Weekday) []string {
	out := make([]string, 0, 7)
	for w := start; w%7 != (end + 1); w++ {
		out = append(out, time.Weekday(w % 7).String()[0:3])
	}
	return out
}

// daysRange generates a string representing a continuous range between given
// day numbers, which due to compatiblilty with old systemd version uses a
// verbose syntax of x,y,z instead of x..z
func daysRange(start, end uint) string {
	var buf bytes.Buffer
	for i := start; i <= end; i++ {
		buf.WriteString(strconv.FormatInt(int64(i), 10))
		if i < end {
			buf.WriteRune(',')
		}
	}
	return buf.String()
}

// generateOnCalendarSchedules converts a schedule into OnCalendar schedules
// suitable for use in systemd *.timer units using systemd.time(7)
// https://www.freedesktop.org/software/systemd/man/systemd.time.html
// XXX: old systemd versions do not support x..y ranges
func generateOnCalendarSchedules(schedule []*timeutil.Schedule) []string {
	calendarEvents := make([]string, 0, len(schedule))
	for _, sched := range schedule {
		days := make([]string, 0, len(sched.WeekSpans))
		for _, week := range sched.WeekSpans {
			abbrev := strings.Join(makeAbbrevWeekdays(week.Start.Weekday, week.End.Weekday), ",")

			if week.Start.Pos == timeutil.EveryWeek && week.End.Pos == timeutil.EveryWeek {
				// eg: mon, mon-fri, fri-mon
				days = append(days, fmt.Sprintf("%s *-*-*", abbrev))
				continue
			}
			// examples:
			// mon1 - Mon *-*-1..7 (Monday during the first 7 days)
			// fri1 - Fri *-*-1..7 (Friday during the first 7 days)

			// entries below will make systemd timer expire more
			// frequently than the schedule suggests, however snap
			// runner evaluates current time and gates the actual
			// action
			//
			// mon1-tue - *-*-1..7 *-*-8 (anchored at first
			// Monday; Monday happens during the 7 days,
			// Tuesday can possibly happen on the 8th day if
			// the month started on Tuesday)
			//
			// mon-tue1 - *-*~1 *-*-1..7 (anchored at first
			// Tuesday; matching Monday can happen on the
			// last day of previous month if Tuesday is the
			// 1st)
			//
			// mon5-tue - *-*~1..7 *-*-1 (anchored at last
			// Monday, the matching Tuesday can still happen
			// within the last 7 days, or on the 1st of the
			// next month)
			//
			// fri4-mon - *-*-22-31 *-*-1..7 (anchored at 4th
			// Friday, can span onto the next month, extreme case in
			// February when 28th is Friday)
			//
			// XXX: since old versions of systemd, eg. 229 available
			// in 16.04 does not support x..y ranges, days need to
			// be enumerated like so:
			// Mon *-*-1..7 -> Mon *-*-1,2,3,4,5,6,7
			//
			// XXX: old systemd versions do not support the last n
			// days syntax eg, *-*~1, thus the range needs to be
			// generated in more verbose way like so:
			// Mon *-*~1..7 -> Mon *-*-22,23,24,25,26,27,28,29,30,31
			// (22-28 is the last week, but the month can have
			// anywhere from 28 to 31 days)
			//
			startPos := week.Start.Pos
			endPos := startPos
			if !week.AnchoredAtStart() {
				startPos = week.End.Pos
				endPos = startPos
			}
			startDay := (startPos-1)*7 + 1
			endDay := (endPos) * 7

			if week.IsSingleDay() {
				// single day, can use the 'weekday' filter
				if startPos == timeutil.LastWeek {
					// last week of a month, which can be
					// 22-28 in case of February, while
					// month can have between 28 and 31 days
					days = append(days,
						fmt.Sprintf("%s *-*-%s", abbrev, daysRange(22, 31)))
				} else {
					days = append(days,
						fmt.Sprintf("%s *-*-%s", abbrev, daysRange(startDay, endDay)))
				}
				continue
			}

			if week.AnchoredAtStart() {
				// explore the edge cases first
				switch startPos {
				case timeutil.LastWeek:
					// starts in the last week of the month and
					// possibly spans into the first week of the
					// next month;
					// month can have between 28 and 31
					// days
					days = append(days,
						// trailing 29-31 that are not part of a full week
						fmt.Sprintf("*-*-%s", daysRange(29, 31)),
						fmt.Sprintf("*-*-%s", daysRange(1, 7)))
				case 4:
					// a range in the 4th week can span onto
					// the next week, which is either 28-31
					// or in extreme case (eg. February with
					// 28 days) 1-7 of the next month
					days = append(days,
						// trailing 29-31 that are not part of a full week
						fmt.Sprintf("*-*-%s", daysRange(29, 31)),
						fmt.Sprintf("*-*-%s", daysRange(1, 7)))
				default:
					// can possibly spill into the next week
					days = append(days,
						fmt.Sprintf("*-*-%s", daysRange(startDay+7, endDay+7)))
				}

				if startDay < 28 {
					days = append(days,
						fmt.Sprintf("*-*-%s", daysRange(startDay, endDay)))
				} else {
					// from the end of the month
					days = append(days,
						fmt.Sprintf("*-*-%s", daysRange(startDay-7, endDay-7)))
				}
			} else {
				switch endPos {
				case timeutil.LastWeek:
					// month can have between 28 and 31
					// days, add trailing 29-31 that are not
					// part of a full week
					days = append(days, fmt.Sprintf("*-*-%s", daysRange(29, 31)))
				case 1:
					// possibly spans from the last week of the
					// previous month and ends in the first week of
					// current month
					days = append(days, fmt.Sprintf("*-*-%s", daysRange(22, 31)))
				default:
					// can possibly spill into the previous week
					days = append(days,
						fmt.Sprintf("*-*-%s", daysRange(startDay-7, endDay-7)))
				}
				if endDay < 28 {
					days = append(days,
						fmt.Sprintf("*-*-%s", daysRange(startDay, endDay)))
				} else {
					days = append(days,
						fmt.Sprintf("*-*-%s", daysRange(startDay-7, endDay-7)))
				}
			}
		}

		if len(days) == 0 {
			// no weekday spec, meaning the timer runs every day
			days = []string{"*-*-*"}
		}

		startTimes := make([]string, 0, len(sched.ClockSpans))
		for _, clocks := range sched.ClockSpans {
			// use expanded clock spans
			for _, span := range clocks.ClockSpans() {
				when := span.Start
				if span.Spread {
					length := span.End.Sub(span.Start)
					if length < 0 {
						// span Start wraps around, so we have '00:00.Sub(23:45)'
						length = -length
					}
					if length > 5*time.Minute {
						// replicate what timeutil.Next() does
						// and cut some time at the end of the
						// window so that events do not happen
						// directly one after another
						length -= 5 * time.Minute
					}
					when = when.Add(randutil.RandomDuration(length))
				}
				if when.Hour == 24 {
					// 24:00 for us means the other end of
					// the day, for systemd we need to
					// adjust it to the 0-23 hour range
					when.Hour -= 24
				}

				startTimes = append(startTimes, when.String())
			}
		}

		for _, day := range days {
			if len(startTimes) == 0 {
				// current schedule is days only
				calendarEvents = append(calendarEvents, day)
				continue
			}

			for _, startTime := range startTimes {
				calendarEvents = append(calendarEvents, fmt.Sprintf("%s %s", day, startTime))
			}
		}
	}
	return calendarEvents
}

// QueryDisabledServices returns a list of all currently disabled snap services
// in the snap.
func QueryDisabledServices(info *snap.Info, pb progress.Meter) ([]string, error) {
	// save the list of services that are in the disabled state before unlinking
	// and thus removing the snap services
	snapSvcStates, err := ServicesEnableState(info, pb)
	if err != nil {
		return nil, err
	}

	disabledSnapSvcs := []string{}
	// add all disabled services to the list
	for svc, isEnabled := range snapSvcStates {
		if !isEnabled {
			disabledSnapSvcs = append(disabledSnapSvcs, svc)
		}
	}

	// sort for easier testing
	sort.Strings(disabledSnapSvcs)

	return disabledSnapSvcs, nil
}