mgmt/engine/resources/hostname.go

// Mgmt
// Copyright (C) James Shubin and the project contributors
// Written by James Shubin <james@shubin.ca> and the project contributors
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// 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 <https://www.gnu.org/licenses/>.
//
// Additional permission under GNU GPL version 3 section 7
//
// If you modify this program, or any covered work, by linking or combining it
// with embedded mcl code and modules (and that the embedded mcl code and
// modules which link with this program, contain a copy of their source code in
// the authoritative form) containing parts covered by the terms of any other
// license, the licensors of this program grant you additional permission to
// convey the resulting work. Furthermore, the licensors of this program grant
// the original author, James Shubin, additional permission to update this
// additional permission if he deems it necessary to achieve the goals of this
// additional permission.

package resources

import (
	"context"
	"errors"
	"fmt"

	"github.com/purpleidea/mgmt/engine"
	"github.com/purpleidea/mgmt/engine/traits"
	engineUtil "github.com/purpleidea/mgmt/engine/util"
	"github.com/purpleidea/mgmt/util"
	"github.com/purpleidea/mgmt/util/errwrap"
	"github.com/purpleidea/mgmt/util/recwatch"

	"github.com/godbus/dbus/v5"
)

func init() {
	engine.RegisterResource("hostname", func() engine.Res { return &HostnameRes{} })
}

const (
	hostname1Path       = "/org/freedesktop/hostname1"
	hostname1Iface      = "org.freedesktop.hostname1"
	dbusPropertiesIface = "org.freedesktop.DBus.Properties"
)

// ErrResourceInsufficientParameters is returned when the configuration of the
// resource is insufficient for the resource to do any useful work.
var ErrResourceInsufficientParameters = errors.New("insufficient parameters for this resource")

// HostnameRes is a resource that allows setting and watching the hostname. If
// you don't specify any parameters, the Name is used. The Hostname field is
// used if none of the other parameters are used. If the parameters are set to
// the empty string, then those variants are not managed by the resource.
type HostnameRes struct {
	traits.Base // add the base methods without re-implementation

	init *engine.Init

	// Hostname specifies the hostname we want to set in all of the places
	// that it's possible. This is the fallback value for all the three
	// fields below. If only this Hostname field is specified, this will set
	// all tree fields (PrettyHostname, StaticHostname, TransientHostname)
	// to this value.
	Hostname string `lang:"hostname" yaml:"hostname"`

	// PrettyHostname is a free-form UTF8 host name for presentation to the
	// user.
	PrettyHostname *string `lang:"pretty_hostname" yaml:"pretty_hostname"`

	// StaticHostname is the one configured in /etc/hostname or a similar
	// file. It is chosen by the local user. It is not always in sync with
	// the current host name as returned by the gethostname() system call.
	StaticHostname *string `lang:"static_hostname" yaml:"static_hostname"`

	// TransientHostname is the one configured via the kernel's
	// sethostbyname(). It can be different from the static hostname in case
	// DHCP or mDNS have been configured to change the name based on network
	// information.
	TransientHostname *string `lang:"transient_hostname" yaml:"transient_hostname"`

	conn *dbus.Conn
}

func (obj *HostnameRes) getHostname() string {
	if obj.Hostname != "" {
		return obj.Hostname
	}

	return obj.Name()
}

func (obj *HostnameRes) getPrettyHostname() string {
	if obj.PrettyHostname != nil {
		return *obj.PrettyHostname // this may be empty!
	}

	return obj.getHostname()
}

func (obj *HostnameRes) getStaticHostname() string {
	if obj.StaticHostname != nil {
		return *obj.StaticHostname // this may be empty!
	}

	return obj.getHostname()
}

func (obj *HostnameRes) getTransientHostname() string {
	if obj.TransientHostname != nil {
		return *obj.TransientHostname // this may be empty!
	}

	return obj.getHostname()
}

// Default returns some sensible defaults for this resource.
func (obj *HostnameRes) Default() engine.Res {
	return &HostnameRes{}
}

// Validate if the params passed in are valid data.
func (obj *HostnameRes) Validate() error {
	a := obj.getPrettyHostname() == ""
	b := obj.getStaticHostname() == ""
	c := obj.getTransientHostname() == ""
	if a && b && c && obj.getHostname() == "" {
		return ErrResourceInsufficientParameters
	}
	return nil
}

// Init runs some startup code for this resource.
func (obj *HostnameRes) Init(init *engine.Init) error {
	obj.init = init // save for later

	return nil
}

// Cleanup is run by the engine to clean up after the resource is done.
func (obj *HostnameRes) Cleanup() error {
	return nil
}

// Watch is the primary listener for this resource and it outputs events.
func (obj *HostnameRes) Watch(ctx context.Context) error {
	recurse := false // single file
	recWatcher, err := recwatch.NewRecWatcher("/etc/hostname", recurse)
	if err != nil {
		return err
	}
	defer recWatcher.Close()

	// if we share the bus with others, we will get each others messages!!
	bus, err := util.SystemBusPrivateUsable() // don't share the bus connection!
	if err != nil {
		return errwrap.Wrapf(err, "failed to connect to bus")
	}
	defer bus.Close()
	// watch the PropertiesChanged signal on the hostname1 dbus path
	args := fmt.Sprintf(
		"type='signal', path='%s', interface='%s', member='PropertiesChanged'",
		hostname1Path,
		dbusPropertiesIface,
	)
	if call := bus.BusObject().Call(engineUtil.DBusAddMatch, 0, args); call.Err != nil {
		return errwrap.Wrapf(call.Err, "failed to subscribe to DBus events for hostname1")
	}
	defer bus.BusObject().Call(engineUtil.DBusRemoveMatch, 0, args) // ignore the error

	signals := make(chan *dbus.Signal, 10) // closed by dbus package
	bus.Signal(signals)

	obj.init.Running() // when started, notify engine that we're running

	var send = false // send event?
	for {
		select {
		case _, ok := <-signals:
			if !ok { // channel shutdown
				return fmt.Errorf("unexpected close")
			}
			//signals = nil
			send = true

		case event, ok := <-recWatcher.Events():
			if !ok { // channel shutdown
				return fmt.Errorf("unexpected close")
			}
			if err := event.Error; err != nil {
				return err
			}
			if obj.init.Debug { // don't access event.Body if event.Error isn't nil
				obj.init.Logf("event(%s): %v", event.Body.Name, event.Body.Op)
			}
			send = true

		case <-ctx.Done(): // closed by the engine to signal shutdown
			return nil
		}

		// do all our event sending all together to avoid duplicate msgs
		if send {
			send = false
			obj.init.Event() // notify engine of an event (this can block)
		}
	}
}

func (obj *HostnameRes) updateHostnameProperty(object dbus.BusObject, expectedValue, property, setterName string, apply bool) (bool, error) {
	propertyObject, err := object.GetProperty("org.freedesktop.hostname1." + property)
	if err != nil {
		return false, errwrap.Wrapf(err, "failed to get org.freedesktop.hostname1.%s", property)
	}
	if propertyObject.Value() == nil {
		return false, fmt.Errorf("unexpected nil value received when reading property %s", property)
	}

	propertyValue, ok := propertyObject.Value().(string)
	if !ok {
		return false, fmt.Errorf("received unexpected type as %s value, expected string got '%T'", property, propertyValue)
	}

	// expected value and actual value match => checkOk
	if propertyValue == expectedValue {
		return true, nil
	}

	// nothing to do anymore
	if !apply {
		return false, nil
	}

	// attempting to apply the changes
	if err := object.Call("org.freedesktop.hostname1."+setterName, 0, expectedValue, false).Err; err != nil {
		return false, errwrap.Wrapf(err, "failed to call org.freedesktop.hostname1.%s", setterName)
	}
	obj.init.Logf("changed %s: `%s` => `%s`", property, propertyValue, expectedValue)

	// all good changes should now be applied again
	return false, nil
}

// CheckApply method for Hostname resource.
func (obj *HostnameRes) CheckApply(ctx context.Context, apply bool) (bool, error) {
	conn, err := util.SystemBusPrivateUsable()
	if err != nil {
		return false, errwrap.Wrapf(err, "failed to connect to the private system bus")
	}
	defer conn.Close()

	hostnameObject := conn.Object(hostname1Iface, hostname1Path)

	checkOK := true
	if h := obj.getPrettyHostname(); h != "" {
		propertyCheckOK, err := obj.updateHostnameProperty(hostnameObject, h, "PrettyHostname", "SetPrettyHostname", apply)
		if err != nil {
			return false, err
		}
		checkOK = checkOK && propertyCheckOK
	}
	if h := obj.getStaticHostname(); h != "" {
		propertyCheckOK, err := obj.updateHostnameProperty(hostnameObject, h, "StaticHostname", "SetStaticHostname", apply)
		if err != nil {
			return false, err
		}
		checkOK = checkOK && propertyCheckOK
	}
	if h := obj.getTransientHostname(); h != "" {
		propertyCheckOK, err := obj.updateHostnameProperty(hostnameObject, h, "Hostname", "SetHostname", apply)
		if err != nil {
			return false, err
		}
		checkOK = checkOK && propertyCheckOK
	}

	return checkOK, nil
}

// Cmp compares two resources and returns an error if they are not equivalent.
func (obj *HostnameRes) Cmp(r engine.Res) error {
	// we can only compare HostnameRes to others of the same resource kind
	res, ok := r.(*HostnameRes)
	if !ok {
		return fmt.Errorf("not a %s", obj.Kind())
	}

	if engineUtil.StrPtrCmp(obj.PrettyHostname, res.PrettyHostname) != nil {
		return fmt.Errorf("the PrettyHostname differs")
	}
	if engineUtil.StrPtrCmp(obj.StaticHostname, res.StaticHostname) != nil {
		return fmt.Errorf("the StaticHostname differs")
	}
	if engineUtil.StrPtrCmp(obj.TransientHostname, res.TransientHostname) != nil {
		return fmt.Errorf("the TransientHostname differs")
	}

	return nil
}

// HostnameUID is the UID struct for HostnameRes.
type HostnameUID struct {
	engine.BaseUID

	name              string
	prettyHostname    string
	staticHostname    string
	transientHostname string
}

// UIDs includes all params to make a unique identification of this object. Most
// resources only return one, although some resources can return multiple.
func (obj *HostnameRes) UIDs() []engine.ResUID {
	x := &HostnameUID{
		BaseUID:           engine.BaseUID{Name: obj.Name(), Kind: obj.Kind()},
		name:              obj.Name(),
		prettyHostname:    obj.getPrettyHostname(),
		staticHostname:    obj.getStaticHostname(),
		transientHostname: obj.getTransientHostname(),
	}
	return []engine.ResUID{x}
}

// UnmarshalYAML is the custom unmarshal handler for this struct. It is
// primarily useful for setting the defaults.
func (obj *HostnameRes) UnmarshalYAML(unmarshal func(interface{}) error) error {
	type rawRes HostnameRes // indirection to avoid infinite recursion

	def := obj.Default()          // get the default
	res, ok := def.(*HostnameRes) // put in the right format
	if !ok {
		return fmt.Errorf("could not convert to HostnameRes")
	}
	raw := rawRes(*res) // convert; the defaults go here

	if err := unmarshal(&raw); err != nil {
		return err
	}

	*obj = HostnameRes(raw) // restore from indirection with type conversion!
	return nil
}