resources: Add new hostname resource

This resource allows to set and watch the hostname on a system.

Signed-off-by: Vinzenz Feenstra <vfeenstr@redhat.com>

DOCUMENTATION.md

@@ -218,6 +218,7 @@ parameter with the [Noop](#Noop) resource.
 
 * [Exec](#Exec): Execute shell commands on the system.
 * [File](#File): Manage files and directories.
+* [Hostname](#Hostname): Manages the hostname on the system.
 * [Msg](#Msg): Send log messages.
 * [Noop](#Noop): A simple resource that does nothing.
 * [Pkg](#Pkg):  Manage system packages with PackageKit.
@@ -263,6 +264,30 @@ The force property is required if we want the file resource to be able to change
 a file into a directory or vice-versa. If such a change is needed, but the force
 property is not set to `true`, then this file resource will error.
 
+###Hostname
+
+The hostname resource manages static, transient/dynamic and pretty hostnames
+on the system and watches them for changes.
+
+#### static_hostname
+The static hostname 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.
+
+#### transient_hostname
+The transient / dynamic hostname 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.
+
+#### pretty_hostname
+The pretty hostname is a free-form UTF8 host name for presentation to the user.
+
+#### hostname
+Hostname is the fallback value for all 3 fields above, if only `hostname` is
+specified, it will set all 3 fields to this value.
+
 ###Msg
 
 The msg resource sends messages to the main log, or an external service such

examples/hostname.yml

@@ -0,0 +1,7 @@
+---
+graph: mygraph
+resources:
+  hostname:
+    - name: Hostname Watcher @ TestHost
+      hostname: test.hostname.example.com
+edges: []

resources/hostname.go

@@ -0,0 +1,326 @@
+// Mgmt
+// Copyright (C) 2013-2016+ 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 Affero 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 Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package resources
+
+import (
+	"encoding/gob"
+	"errors"
+	"fmt"
+	"log"
+	"time"
+
+	"github.com/purpleidea/mgmt/event"
+	"github.com/purpleidea/mgmt/util"
+
+	"github.com/godbus/dbus"
+	errwrap "github.com/pkg/errors"
+)
+
+// 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")
+
+func init() {
+	gob.Register(&HostnameRes{})
+}
+
+const (
+	hostname1Path  = "/org/freedesktop/hostname1"
+	hostname1Iface = "org.freedesktop.hostname1"
+	dbusAddMatch   = "org.freedesktop.DBus.AddMatch"
+)
+
+// HostnameRes is a resource that allows setting and watching the 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.
+//
+// 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.
+//
+// PrettyHostname is a free-form UTF8 host name for presentation to the user.
+//
+// Hostname is the fallback value for all 3 fields above, if only Hostname is
+// specified, it will set all 3 fields to this value.
+type HostnameRes struct {
+	BaseRes           `yaml:",inline"`
+	Hostname          string `yaml:"hostname"`
+	PrettyHostname    string `yaml:"pretty_hostname"`
+	StaticHostname    string `yaml:"static_hostname"`
+	TransientHostname string `yaml:"transient_hostname"`
+
+	conn *dbus.Conn
+}
+
+// NewHostnameRes is a constructor for this resource. It also calls Init() for you.
+func NewHostnameRes(name, staticHostname, transientHostname, prettyHostname string) (*HostnameRes, error) {
+	obj := &HostnameRes{
+		BaseRes: BaseRes{
+			Name: name,
+		},
+		PrettyHostname:    prettyHostname,
+		StaticHostname:    staticHostname,
+		TransientHostname: transientHostname,
+	}
+	return obj, obj.Init()
+}
+
+// Init runs some startup code for this resource.
+func (obj *HostnameRes) Init() error {
+	obj.BaseRes.kind = "Hostname"
+	if obj.PrettyHostname == "" {
+		obj.PrettyHostname = obj.Hostname
+	}
+	if obj.StaticHostname == "" {
+		obj.StaticHostname = obj.Hostname
+	}
+	if obj.TransientHostname == "" {
+		obj.TransientHostname = obj.Hostname
+	}
+	return obj.BaseRes.Init() // call base init, b/c we're overriding
+}
+
+// Validate if the params passed in are valid data.
+// FIXME: where should this get called ?
+func (obj *HostnameRes) Validate() error {
+	if obj.PrettyHostname == "" && obj.StaticHostname == "" && obj.TransientHostname == "" {
+		return ErrResourceInsufficientParameters
+	}
+	return nil
+}
+
+// Watch is the primary listener for this resource and it outputs events.
+func (obj *HostnameRes) Watch(processChan chan event.Event) error {
+	if obj.IsWatching() {
+		return nil // TODO: should this be an error?
+	}
+	obj.SetWatching(true)
+	defer obj.SetWatching(false)
+	cuid := obj.converger.Register()
+	defer cuid.Unregister()
+
+	var startup bool
+	Startup := func(block bool) <-chan time.Time {
+		if block {
+			return nil // blocks forever
+			//return make(chan time.Time) // blocks forever
+		}
+		return time.After(time.Duration(500) * time.Millisecond) // 1/2 the resolution of converged timeout
+	}
+
+	// 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.Wrap(err, "Failed to connect to bus")
+	}
+	defer bus.Close()
+	callResult := bus.BusObject().Call(
+		"org.freedesktop.DBus.AddMatch", 0,
+		fmt.Sprintf("type='signal',path='%s',interface='org.freedesktop.DBus.Properties',member='PropertiesChanged'", hostname1Path))
+	if callResult.Err != nil {
+		return errwrap.Wrap(callResult.Err, "Failed to subscribe to DBus events for hostname1")
+	}
+
+	signals := make(chan *dbus.Signal, 10) // closed by dbus package
+	bus.Signal(signals)
+
+	var send = false // send event?
+	var dirty = false
+
+	for {
+		obj.SetState(ResStateWatching) // reset
+		select {
+		case <-signals:
+			cuid.SetConverged(false)
+			send = true
+			dirty = true
+
+		case event := <-obj.Events():
+			cuid.SetConverged(false)
+			// we avoid sending events on unpause
+			if exit, _ := obj.ReadEvent(&event); exit {
+				return nil // exit
+			}
+			send = true
+			dirty = true
+
+		case <-cuid.ConvergedTimer():
+			cuid.SetConverged(true) // converged!
+			continue
+
+		case <-Startup(startup):
+			cuid.SetConverged(false)
+			send = true
+		}
+
+		// do all our event sending all together to avoid duplicate msgs
+		if send {
+			startup = true // startup finished
+			send = false
+			if dirty {
+				dirty = false
+				obj.isStateOK = false // something made state dirty
+			}
+			// only do this on certain types of events
+			if exit, err := obj.DoSend(processChan, ""); exit || err != nil {
+				return err // we exit or bubble up a NACK...
+			}
+		}
+	}
+}
+
+func updateHostnameProperty(object dbus.BusObject, expectedValue, property, setterName string, apply bool) (checkOK bool, err 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, errwrap.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
+	log.Printf("Changing %s: %s => %s", property, propertyValue, expectedValue)
+	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)
+	}
+
+	// all good changes should now be applied again
+	return false, nil
+}
+
+// CheckApply method for Hostname resource.
+func (obj *HostnameRes) CheckApply(apply bool) (checkOK bool, err error) {
+	log.Printf("%v[%v]: CheckApply(%t)", obj.Kind(), obj.GetName(), apply)
+
+	if obj.isStateOK { // cached state
+		return true, nil
+	}
+
+	conn, err := util.SystemBusPrivateUsable()
+	if err != nil {
+		return false, errwrap.Wrap(err, "Failed to connect to the private system bus")
+	}
+	defer conn.Close()
+
+	hostnameObject := conn.Object(hostname1Iface, hostname1Path)
+
+	checkOK = true
+	if obj.PrettyHostname != "" {
+		propertyCheckOK, err := updateHostnameProperty(hostnameObject, obj.PrettyHostname, "PrettyHostname", "SetPrettyHostname", apply)
+		if err != nil {
+			return false, err
+		}
+		checkOK = checkOK && propertyCheckOK
+	}
+	if obj.StaticHostname != "" {
+		propertyCheckOK, err := updateHostnameProperty(hostnameObject, obj.StaticHostname, "StaticHostname", "SetStaticHostname", apply)
+		if err != nil {
+			return false, err
+		}
+		checkOK = checkOK && propertyCheckOK
+	}
+	if obj.TransientHostname != "" {
+		propertyCheckOK, err := updateHostnameProperty(hostnameObject, obj.TransientHostname, "Hostname", "SetHostname", apply)
+		if err != nil {
+			return false, err
+		}
+		checkOK = checkOK && propertyCheckOK
+	}
+
+	if apply || checkOK {
+		obj.isStateOK = true
+	}
+
+	return checkOK, nil
+}
+
+// HostnameUID is the UID struct for HostnameRes.
+type HostnameUID struct {
+	BaseUID
+	name              string
+	prettyHostname    string
+	staticHostname    string
+	transientHostname string
+}
+
+// AutoEdges returns the AutoEdge interface. In this case no autoedges are used.
+func (obj *HostnameRes) AutoEdges() AutoEdge {
+	return nil
+}
+
+// GetUIDs 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) GetUIDs() []ResUID {
+	x := &HostnameUID{
+		BaseUID:           BaseUID{name: obj.GetName(), kind: obj.Kind()},
+		name:              obj.Name,
+		prettyHostname:    obj.PrettyHostname,
+		staticHostname:    obj.StaticHostname,
+		transientHostname: obj.TransientHostname,
+	}
+	return []ResUID{x}
+}
+
+// GroupCmp returns whether two resources can be grouped together or not.
+func (obj *HostnameRes) GroupCmp(r Res) bool {
+	return false
+}
+
+// Compare two resources and return if they are equivalent.
+func (obj *HostnameRes) Compare(res Res) bool {
+	switch res := res.(type) {
+	// we can only compare HostnameRes to others of the same resource
+	case *HostnameRes:
+		if !obj.BaseRes.Compare(res) { // call base Compare
+			return false
+		}
+		if obj.Name != res.Name {
+			return false
+		}
+		if obj.PrettyHostname != res.PrettyHostname {
+			return false
+		}
+		if obj.StaticHostname != res.StaticHostname {
+			return false
+		}
+		if obj.TransientHostname != res.TransientHostname {
+			return false
+		}
+	default:
+		return false
+	}
+	return true
+}

yamlgraph/gconfig.go

@@ -58,6 +58,7 @@ type Resources struct {
 	// in alphabetical order
 	Exec     []*resources.ExecRes     `yaml:"exec"`
 	File     []*resources.FileRes     `yaml:"file"`
+	Hostname []*resources.HostnameRes `yaml:"hostname"`
 	Msg      []*resources.MsgRes      `yaml:"msg"`
 	Noop     []*resources.NoopRes     `yaml:"noop"`
 	Pkg      []*resources.PkgRes      `yaml:"pkg"`